Layered double hydroxide-based single-atom catalysts: precise catalyst design on a two-dimensional ‘atomic canvas’

In situ synthesis strategy

The in situ synthesis strategy can be likened to ‘integrating pigments directly into the wet canvas during the creation’. In this approach, the single-atom metal species are incorporated concurrently with the precursor for the formation of the LDH support, enabling their direct embedding into the host lattice or anchoring onto the growing crystal surfaces.

Among various in situ routes, co-precipitation stands out for its simplicity and effectiveness. The method involves the simultaneous precipitation of metal salts, including those forming the LDH layers and the single-atom precursor, in an alkaline environment. During LDH crystallization, the target metal atoms are directly embedded within the lattice or firmly anchored on the surface. A representative example is the work by Dong et al., who incorporated single Ru atoms into a CoCr-LDH matrix via one-step co-precipitation using Na₂CO₃ and NaOH for pH control [Figure 2A]^[39]. Through comprehensive characterizations, including X-ray Diffraction (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure (XAFS) and X-ray Photoelectron Spectroscopy (XPS), they confirmed the atomic dispersion and successful integration of Ru species into the LDH framework.

Figure 2. Techniques for ‘painting’ single atoms on the LDH canvas. The synthesis strategies illustrated are (A) coprecipitation. Reprinted with permission from Ref.^[39]. Copyright 2020, Wiley-VCH; (B) hydrothermal. Reprinted with permission from Ref.^[40]. Copyright 2020, Wiley-VCH; (C) electrodeposition. Reprinted with permission from Ref.^[42]. Copyright 2021, Springer Nature; (D) cation exchange. Reprinted with permission from Ref.^[45]. Copyright 2020, Wiley-VCH; (E) anion Exchange-electroreduction. Reprinted with permission from Ref.^[48]. Copyright 2021, The Royal Society of Chemistry (F) loading-reduction. Reprinted with permission from Ref.^[56]. Copyright 2023, Wiley-VCH. LDH: Layered double hydroxide.

Hydrothermal synthesis offers another effective in situ pathway, facilitating the crystallization of LDHs and the incorporation of SAs under elevated temperature and pressure in an aqueous environment. For instance, Sun et al. synthesized Rh SACs by hydrothermally treating a mixture of Rh, Ni, and V precursors on a nickel foam substrate at 120 °C [Figure 2B]^[40]. The obtained Rh₁/NiV-LDH nanosheets were shown by XRD, Energy-Dispersive X-ray Spectroscopy (EDS), and XAFS analyses to contain uniformly dispersed Rh SAs within the LDH matrix. In a related study, Hu et al. first prepared Ru-NiFeAl-LDHs via a glycol-assisted hydrothermal process, followed by etching of Al³⁺ using 5 M NaOH^[41]. This process generates a large number of structural defects within the NiFe-LDH host structure, these defects subsequently serve as anchoring sites for manganese atoms, thereby stabilising the isolated ruthenium atoms and ultimately leading to the preparation of the catalyst (Ru SAs/D-NiFe LDH).

Beyond solution-based methods, electrochemical deposition provides an alternative in situ route for anchoring SAs onto LDH supports. Here, metal ions from the electrolyte are electrochemically reduced and directly deposited as isolated atoms onto the LDH surface under controlled potential or current. For example, Zhai et al. employed a potentiostatic electrodeposition strategy followed by alkaline post-treatment to fabricate Ru SAs/Defect-NiFe LDH [Figure 2C]^[42]. XPS and XAFS analyses demonstrated strong electronic coupling between the anchored Ru SAs and the defective NiFe-LDH support, confirming the effective stabilization of Ru at the defect sites.

Post-synthesis strategy

The post-synthesis strategy can be conceptually regarded as a process of ‘secondary creation on a pre-fabricated LDH canvas’. In this approach, the LDH support is first prepared as a structural matrix, after which single-atom metal species are introduced onto or into the host material through various anchoring pathways. Compared to in situ synthesis, post-synthetic routes offer greater flexibility in selecting metal precursors and enable more precise control over single-atom loading and coordination environments. Among these, ion-exchange methods are widely employed, which typically involve replacing original metal cations or interlayer anions in pre-formed LDHs with target metal species via solution-phase or electrochemical processes^[43,44].

Cation exchange is one effective pathway. For example, Hu et al. first transfomed zeolite-imidazole framework (ZIF)-67 into a hollow-structured material (AC-FeCoNi-LDH) through a simple ion-exchange process in an organic solvent^[45]. Ru³⁺ ions were then introduced to exchange with Fe, Co, and Ni sites, leading to the anchoring of isolated Ru atoms and yielding Ru SAs/AC-FeCoNi [Figure 2D]. In another study, Israr et al. used MIL-88A as a sacrificial template to prepare NiFe-LDH hollow nanocages^[46]. In a weak alkaline environment (0.02 M NaOH), Ru³⁺ ions coordinated with surface hydroxyl/oxygen groups and partially substituted Ni or Fe sites, forming stable Ru-O-M (M = Ni, Fe) bonds to produce Ru-SAC/NiFe-LDH. He et al. demonstrated that Rh³⁺, due to its higher charge density, could replace Ca²⁺ in CaAl-LDH via isostructural substitution, achieving a high Rh loading of 4 wt.% in the resulting Rh₁CaAl-LDH catalyst^[47].

Besides cation exchange, anion-exchange coupled with reduction also serves as an effective route. Chen et al. exchanged interlayer CO₃^2- with PtCl₆^2- to form a precursor (Ni₃Fe-PtCl₆^2- LDH), which was then electrochemically reduced to yield isolated Pt atoms confined in the interlayer regions, forming Ni₃Fe-CO₃^2- LDH-Pt SA [Figure 2E]^[48]. It is worth noting that the efficiency of anion-exchange is often constrained by the lateral size and layer stacking of LDH, necessitating careful control of reaction conditions.

Electrochemical deposition represents another important post-synthesis strategy that enables precise control over single-atom anchoring^[49,50]. By applying constant potential, constant current, or cyclic voltammetry, metal ions in solution can be reduced and deposited as isolated atoms on LDH surfaces or within their porous structures. For instance, Wei et al.^[51], Li et al.^[52], and Liu et al.^[53] constructed isolated Ir sites on Ni-LDH using both cathodic and anodic electrochemical deposition, denoted as Ir₁/Ni-LDH-T and Ir₁/Ni-LDH-V, respectively, demonstrating tunable metal-support interactions and coordination environments.

Another widely used approach is post-loading followed by reduction which typically involves three steps: preparing of the LDH support, loading of metal precursors, and reducing to achieve atomic-level dispersion^[54,55]. For example, Wang et al. immersed MgAl-LDHs in a Ru³⁺ precursor solution for 5 h to allow adsorption via electrostatic and coordination interactions, followed by gas-phase reduction under H₂/Ar at 100 °C for 2 h to form Ru₁/LDH [Figure 2F]^[56]. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) indicated a Ru loading of 1.05 wt.%, while HAADF-STEM, Fourier-transform extend X-ray absorption fine structure (FT-EXAFS), and EDS mapping confirmed the uniform dispersion of Ru SAs. Song et al. adsorbed Ir⁴⁺ on NiFe-LDHs and reduced it with NaBH₄ to form a single-atom alloy (SAA) structure, yielding NiIr-SAA/NiFe-LDH^[57]. In a distinct case, Shen et al. first etched NiFe-LDHs with H₂O₂ to generate oxygen vacancies, then introduced PtCl₄ and conducted hydrothermal reduction^[58]. The resulting Pt/D-NiFe-LDH exhibited Pt-M (Ni, Fe) bonds instead of typical Pt-O-M bonds, illustrating a ‘support-to-metal reverse charge transfer’ mechanism and representing the first stable negatively charged Pt species in an LDH system.

Topological transformation strategy

In addition to in situ and post-synthesis pathways, the topological transformation of LDH precursors offers a versatile and innovative route for constructing SACs^[59,60]. The strategy leverages the structural memory and tunable composition of LDHs, directing their transformations via controlled heating, chemical reduction or intercalation-into derived matrices (e.g., layered double oxides, porous carbon or confined metal frameworks) while largely preserving the original morphology^[61-65]. Throughout the conversion process, single metal atoms can be in situ anchored within the newly formed architecture.

A representative approach involves the transformation of MOFs into LDH-based SACs. For example, Tian et al. started with ZIF-67 (Zn/Co-MOF) as a template, introducing Ni²⁺ and PtCl₆^2- in ethanol^[66]. The hydroxyl groups (-OH) in ethanol partially reduced Pt⁴⁺, while the released Cl- ions triggered the framework’s disintegration and reassembly into a hollow Pt-NiCo LDH that retained the dodecahedral morphology of the parent MOFs. Subsequent calcination at 300 °C in air yielded Pt-NiCo layered double oxide (LDO) nanosheets, in which Pt was present as both SAs and sub-nanometric clusters [Figure 3A].

Figure 3. Schematic illustration of the topology-transformation strategy for synthesizing LDH-based SACs. The pathways include (A) reduction of doped LDH precursors. Reprinted with permission from Ref.^[66]. Copyright 2024, Wiley-VCH; (B) interlayer engineering for confined construction of single-atom sites. Reprinted with permission from Ref.^[67]. Copyright 2021, Elsevier; and (C) interlayer engineering for coordination regulation. Reprinted with permission from Ref.^[68]. Copyright 2020, Wiley-VCH. LDH: Layered double hydroxide; SAC: single-atom catalyst.

In addition, topological transformation based on intercalation engineering offers a powerful route for the precise construction of single-atom sites with specific coordination structures within confined spaces. Yang et al. ingeniously employed this strategy by intercalating the metallomacrocycle Hemin into the interlayer gallery of LDHs^[67]. Subsequent thermal treatment induced the topological conversion of the LDHs host into a LDO due to the well-known ‘memory effect’. Crucially, during the transformation process, the Hemin molecules confined between the layers were pyrolyzed, and their metal centers (Fe) coordinated in situ with nitrogen atoms originating from the Hemin ligands, leading to the formation of well-defined and confined FeN₄ sites [Figure 3B]. The key to the method lies in the fact that the LDHs laminates act not merely as a convertible rigid template but, more importantly, their unique interlayer confinement effect ensures the spatial isolation and fixation of the precursors. The confinement effect effectively suppresses the migration and aggregation of metal atoms during the thermal conversion, ultimately yielding highly uniform single-atom active sites within the LDO matrix.

Furthermore, LDHs can be topologically converted into carbon-supported SACs through pyrolysis and etching. Fan et al. co-intercalated organic molecules [aniline sulfonic acid and p-toluenesulfonic acid (PA)] into CoAl-LDHs^[68]. Upon heating, the LDH layers decomposed, forming Co nanoparticles and a carbon framework from the organic sources. Subsequent HCl etching removed Co nanoparticles, leaving atomically dispersed Co atoms coordinated with N or S within the carbon nanosheets, forming integrated electrode-type SACs (IE-SACs) [Figure 3C].

In summary, the topological transformation strategy enables precise reconstruction of the internal lattice, chemical composition, and coordination environment, while preserving the external geometry, layered topology, and overall morphology of LDHs. The approach not only maintains beneficial features such as ion-transport channels and gas-diffusion pathways but also offers exceptional controllability and tunability in designing SAC architecture, often leading to catalysts with enhanced activity and stability.

Scaled-up production of LDHs

While the in situ synthesis, post-synthesis, and topological transformation strategies described earlier have enabled precise immobilization of SAs on LDHs at the laboratory scale, the practical application of LDH-based SACs hinges on scalable, cost-effective, and environmentally friendly production technologies. LDHs themselves have been industrialized in fields such as flame retardants and polyvinyl chloride (PVC) heat stabilizers. This section focuses on the industrial progress, core technologies, and optimization strategies for LDH scale-up, highlighting their foundational role in mass-producing LDH-based SACs.

The separate Nucleation and Aging Steps Method (SNAS), proposed by Zhao et al. in 2002, is the only industrially validated technology for large-scale nanostructured LDHs synthesis and has been extended to pilot-scale monolayer LDH production^[70]. Unlike conventional coprecipitation (which yields broad particle size distributions of 60 nm ~ 10 μm), the SNAS method decouples nucleation and crystallization: metal salt and alkali solutions are rapidly mixed in a colloid mill for instantaneous, uniform nucleation, followed by separate aging to form well-crystallized LDH nanosheets with a narrow size distribution and tunable thickness [Figure 4A]^[69-71]. Adjusting metal ion ratios (e.g., Mg²⁺/Al³⁺) and process parameters enables precise control over crystal phase and particle size, critical for tailoring the ‘atomic canvas’ for single-atom anchoring^[72]. The SNAS method offers advantages such as simple operation (requiring only a few minutes per batch), excellent reproducibility, and compatibility with LDH compositions, enabling production at the ton-scale level Figure 4B]^[73]. Production lines with capacities of 10,000 tons and higher have been established in multiple regions.

Figure 4. (A) Scale-up production of monolayer LDH nanosheets. Reprinted with permission from Ref.^[69]. Copyright 2021, Elsevier. (B) The separate nucleation and aging steps method is applied in the 100-ton pilot plant and 10000-ton production line of LDHs industrial production from Quzhou Institute for Innovation in Resource Chemical Engineering. Figure 4B is an on-site photograph of the equipment used by our research group at the Quzhou Institute of Resource and Chemical Innovation to synthesize hydrotalcite on an industrial scale using the separate nucleation and aging steps method. LDH: Layered double hydroxide.

In addition, single-layer LDHs exhibit outstanding catalytic performance due to their abundant defects and large specific surface area. However, conventional ‘top-down’ and ‘bottom-up’ synthesis methods for single-layer LDHs are limited to small-scale production (g/day), severely hindering the practical large-scale application of LDH-based materials. Bai et al.^[69] and Chi et al.^[74] employed the SNAS method using a colloid mill reactor to develop a simplified approach for scalable synthesis (~ 50 kg/day) of monolayer LDHs [Figure 4A], yielding multiple varieties of colloidal and powdered monolayer LDHs^[69,74]. The series of single-layer MgAl/CoAl/NiCo/NiFe-LDH nanosheets obtained through this method exhibit a thickness of approximately 1 nm and a high specific surface area of up to 300 m²·g^-1.

In summary, the mass production of LDHs driven by SNAS technology, coupled with green optimization and exfoliation strategies, has effectively overcome bottlenecks in the transition from laboratory to industrial scale. Leveraging the established industrial foundation of LDHs, this approach enables customization of single-atom catalytic carriers, advancing practical applications in energy conversion and environmental remediation. The large-scale preparation of LDH supports the industrialization of SACs by ensuring carrier uniformity (consistent single-atom anchoring sites), structural fidelity (high specific surface area and unsaturated coordination sites), and sustainability (green synthesis meeting industrial requirements).

Electronic modulation engineering: precisely tuning the state of single-atom centers

The performance of SACs is largely determined by the electronic structure of the metal centers, including valence state, charge distribution, and d-band center position. Therefore, precisely tuning the electronic state of single-atom sites to optimize their adsorption strength toward reaction intermediates is a key strategy for improving catalytic activity and selectivity. Owing to their tunable layered composition, abundant surface hydroxyl groups, and unique confined environment, LDHs serve as a highly tailorable platform for stabilizing and engineering SACs. Through strong metal-support interactions (SMSI), interfacial charge transfer, defect engineering, and heteroatom doping, LDHs can effectively modulate the electron density and orbital hybridization of anchored SAs, thereby breaking the linear scaling relationships in traditional catalysis and achieving enhanced catalytic performance. This section will systematically elaborate on the electronic modulation strategies based on LDH supports and their underlying mechanisms in various catalytic reactions.

Ebitani et al. laid the cornerstone for electronic modulation engineering in LDH-based SACs through their pioneering work^[79]. As early as 2005, Ebitani et al. from this team published a landmark study in which they constructed, for the first time, a structurally well-defined hetero-trimetallic single-atom catalytic system (RuMn₂/HT) on a LDH (hydrotalcite, HT) surface^[79]. This work pioneered the use of LDHs as a ‘macro ligand’, leveraging its surface hydroxyl sites to precisely regulate the coordination environment and electronic states of SAs through multi-metallic synergistic effects. The researchers successfully prepared RuMn₂/HT by anchoring manganese Ebitani’s work cations onto the surface of a previously reported Ru/HT catalyst^[79]. Using XAFS spectroscopy combined with reference spectra from RuO₂ and β-MnO₂ for comparative analysis [Figure 5A-D], they confirmed the high dispersion of Ru species and the formation of manganese species on the HT surface. Based on extend X-ray absorption fine structure (EXAFS) curve fitting, they proposed a refined structural model for the hetero-trimetallic species. The model features a Ru⁴⁺ center coordinated by six oxygen atoms, adjacent to Mg cations from the dolomite-like layers of HT and two Mn⁴⁺ cations. This configuration forms a unique Ru⁴⁺-Mn⁴⁺-Mn⁴⁺ structure anchored by hydroxyl groups and water molecules [Figure 5E and F].

Figure 5. Fourier transformation (FT) of the k₃-weighted K-edge EXAFS spectrum of (A) RuO₂; (B) RuMn₂/HT (Ru K-edge); (C) β-MnO₂; and (D) RuMn₂/HT (Mn K-edge). The phase shift was not corrected; (E) Proposed structure of the heterotrimetallic RuMnMn species on HT; (F) RuMn₂/HT Catalyst for the Liquid-Phase Oxidation of Various Alcohols. (A-F) Reprinted with permission from Ref. ^[79]. Copyright 2005, Wiley-VCH. EXAFS: Extended X-ray absorption fine structure; HT: hydrotalcite.

This study did not exist in isolation; it was built upon the team’s prior systematic exploration. For instance, the earlier Ru/HT catalyst reported by Motokura et al. achieved the grafting of Ru⁴⁺ species onto the HT surface, validating the synergistic effect between the metal and the HT support^[80]. Subsequently, the developed Rh/HT catalyst anchored Rh³⁺ species via Rh-O-Mg bonds, expanding the application scope of LDH-supported SACs^[81]. Collectively, these studies established a research paradigm using HT as the support, employing the impregnation method, relying on XAFS as the core characterization technique, and focusing on metal-support synergy.

Therefore, Ebitani’ s work on RuMn₂/HT serves as a pivotal link connecting past and future research. It not only built upon the Ru/HT framework but also innovatively introduced manganese to construct hetero-trimetallic sites, revealing for the first time at the atomic level how LDH supports can be employed to precisely regulate the electronic states of single-atom sites via multimetallic synergy. This work strongly underscores the unique merits of LDHs as a tunable platform for the rational design of precise catalysts, offering critical theoretical and experimental guidance for the development of high-performance multimetallic SACs.

Electronic modulation engineering, which precisely regulates the electronic state of active centers via strong SMSI between LDHs and SAs/composite active sites, serves as the core strategy for constructing high-efficiency water-splitting electrocatalysts^[82]. As a foundational work in this domain, Sun et al. pioneered the concept of reconstruction-free dual-site catalysis by atomically dispersing Ru SAs onto a Ni₃V-LDH scaffold^[83]. The core mechanism, validated by in situ studies and theoretical calculations, relies on SMSI to stabilize the electronic configurations of Ru [hydrogen evolution reaction (HER), active center] and Ni [oxygen evolution reaction (OER), active center], thereby suppressing structural reconstruction during catalytic cycles. Comparative analysis of Ru oxidation state evolution during HER reveals that RuO₂ undergoes a significant reduction in Ru oxidation state under cathodic potentials, while Ru/Ni₃V-LDH exhibits only slight fluctuations - this direct evidence of SMSI-driven stabilization of Ru SAs lays the groundwork for understanding the catalyst’s reconstruction-free nature [Figure 6A]^[83]. Further investigating Ni sites, pure Ni₃V-LDH shows drastic Ni oxidation state reduction during HER and structural rearrangement during OER, whereas Ru/Ni₃V-LDH maintains Ni state stability with minimal bond length variation, highlighting how Ru-Ni electronic coupling enhances structural tolerance against reaction-induced distortion [Figure 6B]. Building on these observations, a schematic diagram illustrates the distinct functional roles of the dual sites: Ru sites dominate proton reduction without structural reconstruction, whereas Ni sites act as OER active centers with stabilized high oxidation states (Ni³⁺/Ni⁴⁺) promoted by Ru. This clearly exemplifies how LDH supports enable the targeted electronic modulation of individual active sites [Figure 6C].

Figure 6. (A) Extracted oxidation state of the Ni site in Ni₃V-LDH and Ru/Ni₃V-LDH samples during HER and OER; (B) Extracted oxidation state of the Ni site in Ni₃V-LDH and Ru/Ni₃V-LDH; (C) Schematic models of HER and OER occurring at steady coordinated dual-active sites on the Ru/Ni₃V-LDH. (A-C) Reprinted with permission from Ref.^[83]. Copyright 2021, American Chemical Society. RHE: Reversible hydrogen electrode; HER: hydrogen evolution reaction; OER: oxygen evolution reaction.

Integrating organic ligand modification and metal doping into LDH-based electronic modulation, Ngo et al. developed an Ir SA anchored on phytic acid (PA)-modified Mn-doped Ni-LDH (Ir@Mn-Ni-PA) via a sequential hydrothermal and coordination assembly strategy^[84]. The phosphate groups of PA form strong metal-oxygen-phosphorus coordination to stabilize Ir SAs, while Mn doping and Ir incorporation synergistically modulate the LDH matrix’s electronic structure, narrowing the bandgap and optimizing intermediate adsorption energies for both HER and OER. Density functional theory (DFT) calculations confirm that Ir SAs donate electrons to the LDH, moderating the binding strength of HER and OER intermediates to align with the Sabatier principle, realizing bidirectional electronic regulation for bifunctional water splitting.

Expanding electronic modulation from single-atom sites to composite active sites, Wu et al. constructed a NiFe LDH-based catalyst by anchoring Pt SAs in Fe vacancies and loading Pt quantum dots on the surface via a two-step strategy^[85]. The dual Pt species form strong electronic interactions with the LDH matrix, and their synergy optimizes the kinetics of water dissociation and hydrogen desorption, realizing collaborative regulation of the HER process. Introducing phase engineering as a new dimension for electronic modulation, Wang et al. prepared Pt SAs supported on an amorphous/crystalline NiFe-LDH heterostructure through two-step electrodeposition^[86]. Pt SAs are uniformly distributed across both phases, and their strong interaction with the heterostructure enhances water adsorption/dissociation efficiency and balances hydrogen intermediate adsorption-desorption, endowing the catalyst with adaptability to diverse electrolytes. Focusing on electronic modulation for OER optimization, Yang et al. stabilized Ru SAs on NiFe-LDH via oxygen-coordination bonds through a facile solution reduction strategy^[54]. Ru SAs trigger electron rearrangement of Ni/Fe sites in the LDH matrix, optimizing the binding energy of OER intermediates and reducing the energy barrier of the rate-determining step (RDS), thereby enhancing intrinsic catalytic activity.

Focusing on site-specific regulation of SMSI without altering LDH supports, Wei et al. developed an electrochemical deposition strategy to anchor Ir SAs on Ni LDH, achieving precise control over metal-support interaction strength^[51]. Cathodic deposition drives Ir atoms to three-fold face-centered cubic (fcc) hollow sites (Ir₁/Ni LDH-T) with strong SMSI, while anodic deposition anchors Ir at oxygen vacancy sites (Ir₁/Ni LDH-V) with weak SMSI, enabling systematic investigation of MSI-activity correlations. Structural models of the two configurations clearly show that Ir₁/Ni LDH-T forms more covalent Ir-O bonds with the support compared to Ir₁/Ni LDH-V. Additionally, charge density difference analysis confirms enhanced electron transfer from Ni LDH to Ir in the strong SMSI system [Figure 7A]. Projected density of states (PDOS) further reveals that strong SMSI tunes the Ir d-band center to a moderate position, balancing intermediate adsorption/desorption strength, whereas weak MSI leads to unfavorable d-band alignment [Figure 7B]. Free energy calculations for OER demonstrate that strong MSI reduces the energy barrier of the RDS (O → OOH) on Ir sites to 1.77 eV, far lower than the 2.34 eV barrier on Ir sites in the weak MSI system [Figure 7C]. Schematic OER pathways illustrate that strong MSI induces a switch of active sites from Ni to Ir [Figure 7D], while weak MSI retains Ni as the dominant active center [Figure 7E]. This site-specific MSI regulation is further corroborated by in situ Raman and isotope-labeling experiments, which confirm the absence of NiOOH redox dynamics in Ir₁/Ni LDH-T during OER [Figure 7F], directly validating the active site switch. This mechanism is vividly summarized in the catalytic pathway diagram, highlighting how SMSI strength dictates active site identity and reaction kinetics.

Figure 7. (A) Top-view schematic structural model of Ir₁/Ni LDH-T and the charge density difference of Ir atoms on Ir₁/Ni LDH-T; (B) In situ Raman spectra of ¹⁸O-labeled Ir₁/Ni LDH-T; (C) Schematic diagram of the oxygen evolution reaction pathway for Ir₁/Ni LDH-T; (D) The top-view schematic structural model of Ir₁/Ni LDH-V and the charge density difference of Ir atoms on Ir₁/Ni LDH-V; (E) In situ Raman spectra of ¹⁸O-labeled Ir₁/Ni LDH-V. (F) Schematic diagram of the oxygen evolution reaction pathway for Ir₁/Ni LDH-V. (A-F) Reprinted with permission from Ref.^[51]. Copyright 2024, Springer Nature. LDH: Layered double hydroxide.

Extending SMSI regulation to chlorine-tolerant seawater HER: Sun et al. used a solvothermal synthesis method to anchor single platinum atoms onto NiV-LDH, where the Pt-O bond induces electronic redistribution to optimize the center of the platinum d-band, whilst vanadium doping generates oxygen vacancies, thereby synergistically regulating the adsorption of intermediates^[87]. This metal-support electronic modulation reduces the energy barriers for H₂O dissociation and *OH desorption, while simultaneously suppressing the adsorption of Cl^- at active sites, thereby endowing the material with inherent chlorine resistance. Targeting biomass upgrading reactions, Xu et al. integrated Lewis acidic Zn clusters into 3D Ru single-atom/NiFeS-LDH, realizing synergistic electronic modulation between Ru SAs and Zn clusters^[88]. Zn clusters increase Lewis acidic oxygen vacancies, regulate the Ni⁰/Ni²⁺ ratio, and stabilize high-valent Ni^2+δ species, while Ru SAs enhance '5-hydroxymethylfurfural (HMF) aldehyde group adsorption - their synergy promotes proton-coupled electron transfer in 5-hydroxymethylfurfural oxidation. Zhang et al. designed a Pt/FeOOH@NiFe LDH catalyst with coexisting Pt SAs and clusters, induced by amorphous FeOOH^[89]. Amorphous FeOOH facilitates H₂O adsorption and activation, while Pt SAs and clusters promote H₂ formation and desorption, synergistically accelerating HER kinetics via the Volmer-Heyrovsky mechanism. Hu et al. stabilized Ru SAs on defective NiFe LDH (Ru SAs/D-NiFe LDH@NF) via hydrothermal synthesis and etching^[41]. Ru SAs regulate electron distribution near LDH defects, optimize Ru-NiFe interaction, and reduce the energy barrier for *OOH intermediate formation, exhibiting excellent OER performance and stability in Zn-air batteries.

Electronic modulation engineering, which regulates the electronic state of active centers via SMSI between LDHs and SACs, is pivotal for developing high-efficiency OER electrocatalysts^[22,90,91]. The work by Li et al. on Ru SAs anchored on cobalt-iron LDH (Ru/CoFe-LDHs) serves as a paradigmatic study, as it systematically deciphers how LDHs modulate single-atom electronic structures through SMSI^[43]. This mechanism is coherently validated by a series of correlated characterizations and theoretical calculations, forming a logical chain from structural identification to catalytic performance optimization^[43]. Fourier-transformed Ru K-edge EXAFS spectra of Ru/CoFe-LDHs (alongside Ru foil, RuCl₃, RuO₂) reveal the absence of Ru-Ru, Ru-Cl, and Ru-O-Ru characteristic peaks, with only Ru-O bonds and weak Ru-O-M (M=Co/Fe) bonds observed. This direct evidence confirms Ru atoms are atomically dispersed on LDHs, laying the structural foundation for SMSI-induced electronic modulation [Figure 8A]. Building on this structural confirmation, model-based EXAFS fitting further quantifies the coordination environment: each Ru atom coordinates with ~ 3.9 oxygen atoms, among which ~ 2.9 Ru-O bonds are linked to Co/Fe atoms of LDHs, enabling efficient electron transfer between Ru and the support and establishing the structural basis for strong electronic coupling [Figure 8B].

Figure 8. (A) Fourier-transformed Ru K-edge EXAFS spectra of Ru/CoFe-LDHs, RuCl₃, RuO₂, and Ru metal; (B) Corresponding model-based fittings of Ru EXAFS for Ru/CoFe-LDHs and simulated EXAFS spectra from Ru-O and Ru-O-M (M = Co or Fe) bonds (the inset is the magnifying local structure of Ru/CoFe-LDHs), showing the exclusive existence of Ru-O-M bonds in Ru/CoFe-LDHs sample. The differential charge density of elements in CoFe-LDHs (C) and Ru/CoFe-LDHs (D) from computational simulation, revealing electron donation from LDHs to Ru. Gibbs free-energy diagram for the four steps of OER on CoFe-LDHs (E) and Ru/CoFe-LDHs (F). (A-F) Reprinted with permission from Ref.^[43]. Copyright 2019, Springer Nature. EXAFS: Extend X-ray absorption fine structure; LDH: layered double hydroxide.

To unravel the essence of electronic modulation, differential charge density comparisons of CoFe-LDHs and Ru/CoFe-LDHs provide critical insights: pristine CoFe-LDHs exhibit uniform electron distribution across the matrix [Figure 8C], while Ru anchoring induces significant electron density reduction at Co/Fe sites and accumulation at Ru sites. This observation verifies electron transfer from LDHs to Ru via Ru-O-M bridging bonds, a core driver for optimizing catalytic activity [Figure 8D]. The impact of electronic modulation on OER kinetics is ultimately clarified by Gibbs free energy diagrams: for pristine CoFe-LDHs, the RDS of (*O → *OOH) exhibits a high energy barrier of 1.94 eV and a theoretical overpotential of 0.71 eV [Figure 8E]. In contrast, Ru/CoFe-LDH retains the same RDS but reduces the barrier to 1.52 eV and overpotential to 0.29 eV [Figure 8F]. This improvement originates from SMSI-tuned d-band centers of Ru, which balance the adsorption/desorption of OER intermediates (*OH, *O, *OOH) and break the scaling relation limitation.

Integrating heterostructure coupling and interface engineering, dual strategies have been developed to enhance electronic modulation for water splitting. Chen et al. constructed a Ru single-atom/NiFe-LDH/MoNiS core-shell heterostructure (RuSA/NiFe-LDH/MoNiS) via sequential hydrothermal and immersion methods, where Ru atoms form Ru-O-Ni motifs on NiFe-LDH^[92]. SMSI-induced electron redistribution between Ru, NiFe-LDH, and MoNiS optimizes the d-band center of Ru, accelerating water dissociation and balancing *H/*OH adsorption-desorption for efficient alkaline HER. Deng et al. anchored single Ru atoms on CoFe-LDH (Ru_0.51-CoFe-LDH) and integrated it with BiVO₄ to form an n-n heterojunction photoanode^[93]. Ru SAs trigger electron rearrangement in CoFe-LDH, inducing a negative shift of its band edge to enhance interfacial band bending, which facilitates photogenerated charge separation and transfer for photoelectrochemical water splitting.

Extending electronic modulation to light-responsive systems, light-induced dynamic regulation of single-atom states has emerged as a novel strategy for photocatalytic CO₂ reduction. Fan et al. anchored Pt SAs on ZnNiTi-LDHs with metal ion vacancies (Pt₁/ZnNiTi-LDHs-E) via defect immobilization after selective Zn²⁺ etching^[94]. Under different light intensities, Pt SAs capture photoelectrons to form Pt(IV), electron-rich Pt(II), and near-neutral Pt^δ+ species. They drive CO generation, C₂H₆ formation via C-C coupling (with Ni²⁺/Ti⁴⁺ sites), and CH₄ production, respectively, via direct hydrogenation, realizing structure-dependent reaction pathway control^[94].

Extending this framework to lattice doping strategies, Dong et al. fabricated Ru lattice-doped CoCr LDHs (CoCrRu LDHs), where single Ru atoms downshift the d states of adjacent Co atoms and enhance electron donation from Cr to oxygenates^[39]. This synergistic charge transfer weakens Co’s adsorption of *O/*OH and strengthens its binding to *OOH, breaking the scaling relation and boosting OER activity. Focusing on iridium single-atom systems, Biswal et al. reported Ir₁/NiCr LDH by anchoring Ir atoms on NiCr LDH via surface hydroxyl groups^[95]. SMSI-induced electron redistribution between Ir and Ni/Cr optimizes Ir’s coordination environment (tetracoordinate Ir-O bonds), reduces the energy barrier of the OER RDS, and endows the catalyst with excellent activity and stability in both alkaline and seawater electrolytes.

Electronic modulation engineering, which regulates the electronic state of active centers via SMSI between LDHs and SACs/dual-atomic catalysts (DACs), remains a core strategy for developing high-efficiency bifunctional oxygen electrocatalysts [oxygen reduction reaction (ORR)/OER] for zinc-air batteries (ZABs)^[96]. Liu et al. constructed a NiFe-LDH/ Fe₁-N-C heterostructure, revealing how LDH nanodots modulate the electronic structure of single-atom Fe₁-N-C through interfacial coupling^[96]. Optimized atomic configurations of ORR elemental steps on NiFe-LDH/Fe₁-N-C clearly show the spatial arrangement of NiFe-LDH nanodots and Fe₁-N-C matrix, with Fe-N₄ moieties identified as ORR active sites and NiFe-LDH as OER active centers. This structural design ensures intimate interfacial contact, laying the foundation for electron transfer between the two components [Figure 9A]^[96]. Building on this structural basis, calculated energy barriers of ORR reveal that the RDS for Fe₁-N-C (hydrogenation of *O₂ to *OOH) has a high energy barrier of 2.59 eV, while NiFe-LDH modification reduces this barrier to 1.96 eV - this reduction originates from the enhanced adsorption and activation of *O₂ by interfacial electronic coupling [Figure 9B]. To decipher the essence of this modulation, differential charge density analysis shows significant electron redistribution: NiFe-LDH donates 1.25 e^- to Fe₁-N-C, with electron accumulation around Fe-N₄ sites and depletion in NiFe-LDH. This charge transfer directly optimizes the binding strength between Fe active sites and ORR intermediates [Figure 9C]. This electronic modulation is further quantified by the d-band center of Fe 3d orbitals: Fe₁-N-C alone has a d-band center of -2.13 eV, while NiFe-LDH coupling upshifts it to -1.45 eV. This upshift increases the number of unoccupied orbitals in Fe 3d, strengthening the interaction with *O₂ and facilitating its activation [Figure 9D].

Figure 9. (A) The optimized atomic configurations of ORR elemental steps on the NiFe-LDH/Fe1-N-C; (B) Calculated energy barrier of ORR on NiFe-LDH/Fe₁-N-C and Fe₁-N-C; (C) Side view of differential charge density by Löwdin charge analysis of NiFe-LDH/Fe₁-N-C heterostructures with an isosurface value of 0.005 e Å^-3. (D) d-Band centers for Fe 3d of NiFe-LDH/Fe₁-N-C and Fe₁-N-C. (A-D) Reprinted with permission from Ref.^[96]. Copyright 2023, Wiley-VCH. LDH: Layered double hydroxide.

Extending this heterostructure coupling strategy to DACs, Qin et al. constructed FeNi-LDH@DACs with a ‘sesame-ball-like’ architecture by anchoring FeNi-LDH nanodots on FeNi DACs^[62]. Electron transfer from LDH to DACs modulates the d-band center of FeNi atomic sites, optimizing oxygen intermediate adsorption energies, and the porous carbon framework of DACs enhances conductivity - this synergy endows the catalyst with a peak power density of 211.6 mW cm^-2 and 500 h cycling stability in ZABs. Focusing on size-confined coupling, Wang et al. fabricated NiFe-ND/FeCo-NC by depositing ultrasmall NiFe-LDH nanodots on 3D flower-like FeCo-NC^[97]. The 3D mesoporous structure of FeCo-NC confines NiFe-LDH growth to ~ 4 nm, and strong interfacial coupling induces electron depletion in Ni sites - this enhances the formation of Ni (Fe)OOH active phases during OER, delivering a small discharge-charge voltage gap of 0.87 V in ZABs.

Coordination engineering

The catalytic performance of SACs is intrinsically linked to the local coordination environment of the active metal centers. Coordination engineering therefore represents a powerful strategy for optimizing SACs by precisely tailoring this microenvironment, including the type and number of coordinating atoms, bond lengths/angles, and the presence of vacancies. For LDH-based SACs, this confers an exceptional capability to precisely regulate the interaction between the SACs and the LDH support. The layered structure of LDHs, with its abundant hydroxyl groups and tunable cation vacancies, provides a unique platform for such engineering. By manipulating the type and distribution of these vacancies (e.g., M²⁺ vs. M³⁺ sites), one can directionally design both the primary coordination shell (directly bonded atoms) and the secondary coordination sphere of the anchored SA^[55]. This precise control over the coordination geometry directly modulates the electronic structure (e.g., oxidation state, d-band center) and, consequently, the adsorption/desorption behavior of key reaction intermediates, enabling rational optimization of catalytic activity and selectivity^[98-101]. Among various approaches, the regulation of cation vacancies to construct well-defined anchoring sites stands out as a pivotal method for stabilizing SAs while fine-tuning their catalytic microenvironments.

Jin et al. utilized NiFe-LDH as a support to construct a series of Ru SACs by regulating M³⁺/M²⁺ cation vacancies^[55]. Employing alkali etching-induced vacancy formation as the core coordination control strategy, NiFeAl-LDH and NiZnFe-LDH were treated with NaOH to selectively remove Al³⁺ and Zn²⁺, respectively, generating M³⁺ vacancies (LDH-V_III) and M²⁺ vacancies (LDH-V_II). Subsequent RuCl₃ impregnation and H₂/Ar reduction anchored Ru SAs at vacancy sites or surface hydroxyl sites of pristine NiFe-LDH, successfully yielding three Ru SACs (Ru₁/LDH-V_III, Ru₁/LDH-V_II, Ru₁/LDH) with distinctly different coordination environments, establishing a foundation for precise coordination structure control [Figure 10A].

Figure 10. (A) Schematic of Ru₁/LDH-V_III, Ru₁/LDH-V_II, Ru₁/LDH synthesis via defect engineering; (B) FT-EXAFS spectra of Ru₁/LDH-V_III/V_II, and refs (Ru foil, RuCl₃, RuO₂); (C) Electron transfer between Ru and NiFe-LDH (M_III/M_II vacancies or none); CO adsorption on (110) surfaces of Ru₁/LDH-V_III/V_II; in situ FT-IR of saturated CO chemisorption; (D) Aerobic oxidation of benzyl alcohol (chemical equation) and plots of conversion-time, TOF, and selectivity. (A-D) Reprinted with permission from Ref. ^[55]. Copyright 2021, Wiley-VCH. LDH: Layered double hydroxide; FT-EXAFS: Fourier-transform extend X-ray absorption fine structure; FT-IR: Fourier transform infrared spectroscopy; TOF: turnover frequency.

Differences in coordination structures are central to regulating catalytic performance. Both Ru₁/LDH-V_III and Ru₁/LDH-V_II exhibit strong Ru-O coordination peaks at 1.62 Å, with Ru-O-M (M = Ni/Fe) secondary coordination peaks detected at 2.2 Å^[55]. This indicates Ru SAs are embedded within LDH layers to form a hexacoordinated configuration (Ru-O₆), where Ru₁/LDH-V_III exhibits a single Ru-O-Ni secondary coordination, while Ru₁/LDH-V_II shows coexisting Ru-O-Ni/Fe coordination; in contrast, the Ru-O peak of Ru₁/LDH appears at 1.44 Å without a secondary coordination peak, confirming its surface tetracoordinate adsorption configuration (Ru-O₄). This difference in coordination number and coordinating atom directly modulates the electronic state of the SA [Figure 10B]. The electronic structure changes further validate the coordination engineering effect. XPS and DFT calculations reveal that in the hexacoordinated Ru₁/LDH-V_III, the Ru 3p_3/2 binding energy reaches 463.6 eV in the Ru₁/LDH-V_III system, exhibiting a +4 oxidation state and transferring 1.50 e^- to the carrier^[55]. This is significantly higher than in the tetracoordinate Ru₁/LDH system (463.1 eV, 0 ~ +3 oxidation state, transferring 0.62 e^-). In the CO chemisorption Fourier transform infrared spectroscopy (FT-IR) spectrum, the characteristic peak of Ru₁/LDH-V_III appears at 2,020 cm^-1, indicating the lowest d orbital electron occupancy. This shift originates from the precise modulation of the Ru atom’s electron density by the hexacoordinated environment [Figure 10C]. Catalytic performance testing directly validated the coordination engineering. With the selective aerobic oxidation of benzyl alcohol employed as the probe reaction, the hexacoordinated Ru₁/LDH-V_III catalyst delivered a benzyl alcohol conversion of 99.0% and a turnover frequency (TOF) of 1,331 h^-1 under the reaction conditions of toluene as solvent (3 mL), a Ru-to-benzyl alcohol molar ratio of 1:500, 1 bar O₂ pressure and 90 °C reaction temperature, which was significantly superior to the performance of Ru₁/LDH-V_II (87.7% conversion, 976 h^-1 TOF) and Ru₁/LDH (47.9% conversion, 659 h^-1 TOF)^[55]. Notably, all three Ru SAC systems achieved nearly 100% selectivity for the target product benzaldehyde in this reaction. DFT calculations confirmed that the hexacoordinated Ru-O-Ni environment reduced the benzaldehyde desorption energy barrier to 1.20 eV, whereas the tetracoordinated environment exhibited a barrier as high as 1.91 eV, highlighting the decisive role of coordination geometry in catalytic kinetics [Figure 10D].

Vacancy engineering can be synergistically combined with LDH size control to tailor coordination configurations suitable for photocatalytic applications. Yu et al. extended vacancy-mediated coordination to ultrathin LDHs, anchoring Ru at Al vacancies in ultrathin CoAl-LDH (~ 1.0 wt.% Ru) via formamide-assisted hydrothermal synthesis and wet impregnation, thereby preparing a Ru SAC^[102]. The exfoliation process of ultrathin LDHs preferentially generates Al vacancies (whose formation energy is lower than that of Co vacancies); the Ru SA forms an unsaturated Ru-O₅ coordination with neighboring oxygen atoms, thereby avoiding the aggregation phenomenon observed in bulk LDH-supported Ru catalysts. This coordination environment enhances the adsorption and activation of CO₂ and stabilizes the COOH* intermediate, thereby lowering the protonation energy barrier for photocatalytic CO₂ reduction.

Doping-induced symmetry breaking has emerged as an innovative coordination engineering strategy for creating unsaturated active sites for electrocatalysis. Mu et al. employed symmetry-breaking doping as a coordination control strategy, anchoring Ru SAs onto FeCo-LDH via a mixed-solvent method (Ru_xSACs@FeCo-LDH), thereby breaking the symmetry inherent in the ordered atomic arrangement of FeCo-LDH^[103]. Ru doping at the symmetry-broken interface induced the in situ formation of Ru-O-TM (Fe/Co/Ni) nanocomposites, in which Ru SAs in an unsaturated coordination environment facilitated O-O coupling in the OER reaction. X-ray absorption near edge structure (XANES) and EXAFS analyses confirmed the positive oxidation state of Ru (0 < δ < 4) and the absence of Ru-Ru bonds, whilst DFT calculations indicated that this symmetry-broken structure optimizes the adsorption of intermediates by modulating the d-band centers of the active sites.

Axial ligand modification provides a method for precisely regulating the microenvironment of single-atom coordination without altering the main coordination shell. By engineering the axial ligands to finely tune the coordination microenvironment, Zhang et al. utilized electrodeposition and irradiation-assisted ligand exchange to prepare Pt SACs on NiFe-LDH (X-Pt/LDH, where X = -F, -Cl, -Br, -I, -OH)^[104]. The Pt SA forms a tetrahedral coordination with three surface oxygen atoms of the LDH and one axial ligand; the electronegativity of the ligand modulates the oxidation state of Pt (2.08 for HO-Pt/LDH and 2.78 for Cl-Pt/LDH) and the d-band center. DFT calculations indicate that Cl^- is the optimal axial ligand, as it optimizes the adsorption energies of *H and *OH, thereby accelerating hydrolysis in the alkaline HER while maintaining the dispersion of the Pt atoms.

Extending coordination engineering to defective LDH supports, Zhai et al. stabilized Ru SAs on defective NiFe LDH (Ru₁/D-NiFe LDH) via electrodeposition and etching, where defects provide unsaturated coordination sites to strengthen Ru-O bonding. This coordination environment optimizes H adsorption energies for HER and promotes O-O coupling for OER, enabling an ultralow HER overpotential of 18 mV at 10 mA cm^-2[42]. Focusing on heterointerface coordination, Dao et al. fabricated defect-rich Ru-doped NiFe LDH on NiCo₂O₄ nanowires (def-Ru-NiFe LDH/NCO), where Ru SAs coordinate with oxygen atoms at the heterointerface^[105]. This unique coordination structure induces electronic redistribution, reduces charge transfer resistance, and lowers the OER overpotential to 225 mV at 10 mA cm^-2, with excellent stability over 60 h of operation. Targeting Zn-air battery applications, Hu et al. anchored Ru SAs on defective NiFe LDH (Ru SAs/D-NiFe LDH@NF) via hydrothermal synthesis and etching^[41]. The Ru-O coordination at defect sites regulates electron distribution near vacancies, optimizing the formation of OER intermediates and endowing the catalyst with a maximum power density of 170 mW cm^-2 and 350 h cycling stability in Zn-air batteries.

Using LDH as a catalyst support, precise modulation of electronic structures is achieved by controlling the coordination environment of single-atom and dual-atom catalysts, thereby optimizing the adsorption - desorption behavior of electrocatalytic reaction intermediates. By leveraging the phase structure of LDHs to modulate the coordination environment, Hu et al. developed a Ru SAC supported on a hybrid amorphous/crystalline FeCoNi LDH^[45]. The amorphous outer layer of LDH provides abundant defects and unsaturated coordination sites to stabilize Ru SAs, while the crystalline inner layer ensures carrier rigidity. Electron rearrangement occurs between Ru and Fe/Co/Ni (Ru attracts electrons from Co/Ni and transfers electrons to Fe), lowering the energy barrier for the RDS of OER (Ru-O* formation).

Targeting the coordination advantages of heterointerfaces, Wu et al. anchored Ir single atoms at the NiFe LDH/NiMo heterointerface^[106]. Ir is stabilized through dual Ir-O and Ir-Ni coordination, with its electronic modulation optimizing adsorption strength for key HER/OER intermediates. This catalyst exhibits structural stability in both alkaline water and seawater, as the heterointerface coordination environment effectively suppresses Ir aggregation and dissolution. Employing an innovative dual-single-atom coordination strategy, Liu et al. constructed a CoFe-LDH-based catalyst by anchoring Ru/Ir dual single atoms via oxygen vacancies^[107]. Oxygen vacancies provide stable coordination sites for the dual single atoms. Synergistic electronic regulation between Ru and Ir brings their d-band centers closer to the Fermi level, balancing the adsorption-desorption kinetics of OER intermediates. Electrons transfer from CoFe-LDH to Ru/Ir, forming stable metal-oxygen coordination structures.

By employing LDH as a catalyst support, the coordination environment between single atoms and LDH can be precisely regulated via the construction of specific coordination bonds^[51,53]. This enables precise modulation of the electronic structure at active sites, thereby optimizing the adsorption behavior of electrocatalytic reaction intermediates. The core mechanism relies on the atomic-level control capabilities of coordination engineering.

Focusing on coordination bond regulation and electronic interactions between single atoms and LDH, Hu et al. synthesized Ir single-atom/NiFe LDH systems (Ir_SAC-NiFe-LDH and NiIr_SAA-NiFe-LDH)^[57]. Analysis of charge density differences clearly reveals electron transfer patterns. In NiIr_SAA-NiFe-LDH, Ir atoms exhibit electron enrichment (-0.15 e^-), while Ni atoms show electron deficiency (0.15 e^-), confirming directed electron transfer from Ni to Ir [Figure 11A]. Conversely, in Ir_SAC-NiFe-LDH, both Ir and its neighboring Ni atoms lose electrons, which accumulate toward oxygen species, forming a unique electron redistribution pattern [Figure 11B]. Based on electronic structure characteristics, adsorption site preferences were further clarified: Ni sites in NiIr_SAA-NiFe-LDH are the preferred adsorption sites for HER. In Ir_SAC-NiFe-LDH, Ni sites adjacent to Ir are the optimal adsorption sites for OER, with the coordination environment determining the functional division of active centers [Figure 11C]. Free energy calculations quantified this coordination-driven effect: NiIr_SAA-NiFe-LDH exhibits hydrogen adsorption free energy (-0.17 eV) closer to the ideal value, while Ir SAC-NiFe-LDH reduces the energy barrier at the RDS for OER. Both improvements stem from coordination-induced optimization of electronic states [Figure 11D].

Figure 11. Top and side views of differential charge densities of (A) Nilr_SAA-NiFe-LDH and (B) lr_SAC-NiFe-LDH. Gibbs free energy dagrams for (c) the HER at U = 0 and (D) OER at U =1.23 V on Nilr_SAA-NiFe-LDH, lr_SAC-NiFe-LDH, and NiFe-LDH. (A-D) Reprinted with permission from Ref. ^[57]. Copyright 2023, American Chemical Society. LDH: Layered double hydroxide; SAA: single-atom alloy; SAC: single-atom catalyst; HER: hydrogen evolution reaction; OER: oxygen evolution reaction.

Extending the coordination engineering strategy of Pt and LDH, Hu et al. constructed the ePt/NiFe LDH@e-nf catalyst via electrodeposition^[53]. This unique Pt-Ni/Fe coordination bond replaces the conventional Pt-O-M bond, enabling direct electronic regulation of the metal centers. This coordination pattern elevates the valence state of Ni/Fe while optimizing the electron density at Pt sites. Electron transfer from Ni/Fe to Pt enhances interactions between intermediates and active sites, aligning closely with the core logic of Pt-Ni coordination-driven electronic structure regulation.

Building upon defect-assisted coordination innovation, Shen et al. designed a Pt SAC supported on oxygen-defect-doped NiFe LDH (D-NiFe-LDH)^[58]. By substituting conventional Pt-O bonds with Pt-Ni electronic bridges, oxygen defects further promote electron transfer from Ni to Pt, inducing Pt to adopt a negative valence state. This coordination environment regulation not only optimizes electron distribution but also shifts the d-band center position of Pt, weakening hydrogen adsorption strength. Its mechanism aligns with the Pt-Ni/Fe coordination electron regulation logic, representing an extension of Pt-LDH coordination engineering exploration.

Focusing on multi-coordination regulation of Ir with LDH, Duan et al. proposed a dynamic Cl^- adsorption-assisted coordination strategy, forming unique Ir-OH/Cl mixed coordination in Ir/CoFe-LDH^[108]. Dynamic Cl^- adsorption optimizes Ir’s electronic structure through electron-induced effects, lowering the energy barrier of the oxygen evolution RDS (*O → *OOH). This approach of electronic regulation via coordination atom substitution aligns with the core logic of Ir single-atom coordination engineering. To expand the bidirectional coordination interactions in Ir-LDH, Cao et al. anchored Ir single atoms onto the CoFe-LDH/reduced graphene oxide (rGO) surface through Ir-O-M (M=Co/Fe) coordination^[44]. LDH modulates Ir’s electronic state via coordinate bonds, while Ir sites stabilize Fe sites through electronic coupling, forming a ‘carrier-single atom’ bidirectional coordination regulation system. Its mechanism centers on coordination-induced electronic synergy, consistent with the coordination engineering strategy of Ir-LDH.

Focusing on single-atom-cluster synergy and intra-layer coordination strategies, Tian et al. precisely introduced Pt SAs and Pt clusters into NiCo LDO layers via a dual-ion etching-phase transition method^[66]. Pt SAs insert into LDO layers, occupying partial Ni sites to form Pt-Co bonds. This synergizes with surface Pt clusters, enhancing Pt-NiCo LDO electronic interactions. It promotes preferential adsorption of H* species onto O sites above Pt SAs, accelerating water-splitting kinetics in the Volmer step. The core mechanism lies in intra-layer coordination and synergistic electronic regulation between single atoms and clusters. Leveraging the unique advantages of interfacial coordination engineering, Wu et al. anchored Ir single atoms at the NiFe LDH/NiMo interface to construct a bifunctional catalyst^[106]. The Ir single atom is stabilized by dual Ir-O and Ir-Ni coordination, inducing electron transfer from NiMo to NiFe LDH while establishing directed electron redistribution among Ir, Ni, and Fe sites. This precisely optimizes the adsorption strength of key HER/OER intermediates, with the core mechanism originating from heterointerfacial coordination-induced multi-component electronic synergy modulation.

Microenvironment confinement-mass transfer

Beyond simply anchoring active sites, the true power of LDHs as an ‘atomic canvas’ lies in their ability to orchestrate both the local chemical environment of single atoms and the macroscopic transport of reactants and products. Microenvironment confinement-mass transfer synergy has thus emerged as a key strategy for reconstructing catalytic interfaces and unlocking multifunctional performance in LDH-based catalysts^[109,110]. This dual-control paradigm leverages the structural versatility of LDHs. On one hand, their designable architectures (e.g., monolayer nanosheets, porous frameworks, and heterojunction couplings) can be engineered to optimize mass transport pathways, reduce diffusion resistance, and expose abundant accessible surfaces. On the other hand, their unique layered and confined spaces (e.g., interlayer galleries, defect sites, and interfacial domains) enable precise tailoring of the local microenvironment surrounding the active sites, including coordination geometry, electronic density, and intermediate stabilization^[111,112]. By synergistically integrating confinement effects (which stabilize single atoms and modulate reaction pathways) with optimized mass transfer (which ensures efficient supply of reactants and removal of products), this approach significantly enhances catalytic kinetics, selectivity, and long-term stability, as evidenced by a growing body of representative studies.

Wang et al. loaded single-atom Ru (Ru₁/mono-NiFe) onto monolayer NiFe LDH^[113]. Transmission electron microscopy (TEM) images reveal that both monolayer NiFe and Ru₁/mono-NiFe exhibit uniform monolayer nanosheet morphology with lateral dimensions of approximately 30 nm and thickness of about 1 nm, retaining the layered structure of LDH after ruthenium anchoring [Figure 12A and B]^[113]. High-resolution transmission electron microscopy (HRTEM) confirmed a lattice fringe spacing of 0.15 nm, corresponding to the (110) plane of LDH, verifying the structural integrity of the support [Figure 12C]. HAADF-STEM revealed uniformly distributed isolated bright spots on the monolayer LDH surface, confirming atomically dispersed Ru without aggregation [Figure 12D].

Figure 12. TEM images of (A) mono-NiFe and (B) Ru₁/mono-NiFe-0.3; (C) HRTEM image of Ru₁/mono-NiFe-0.3; (D) HAADF-STEM image of Ru₁/mono-NiFe-0.3; (E) The Ru K-edge XANES spectra; (F) the Ru K-edge EXAFS k²χ functions for Ru₁/mono-NiFe-1.6, Ru₁/mono-NiFe-0.3, RuCl₃, RuO₂ and Ru Foil; (G) the wavelet transforms for the k²-weighted EXAFS signals of Ru₁/mono-NiFe-0.3, RuO₂ and Ru Foil; (H) the magnitude of k²-weighted Fourier transforms of the Ru K-edge EXAFS spectra for Ru₁/mono-NiFe-0.3, Ru₁/mono-NiFe-1.6, RuO₂ and Ru Foil; (I) schematic illustration of Ru₁/mono-NiFe-x. (A-I) Reprinted with permission from Ref.^[113] Copyright 2019, The Royal Society of Chemistry. TEM: Transmission electron microscopy; HRTEM: high-resolution transmission electron microscopy; HAADF-STEM: high-angle annular dark-field scanning transmission electron microscopy; XANES: X-ray absorption near edge structure; EXAFS: extend X-ray absorption fine structure.

To characterize the microenvironment and electronic structure of Ru SAs, the XANES and extended EXAFS analyses were performed. The Ru K-edge XANES spectrum of the single-atom NiFe system exhibits an absorption position consistent with RuCl₃, indicating Ru exists in the +3 oxidation state [Figure 12E]. The k²-weighted EXAFS oscillation spectrum of the single-atom NiFe system shows significant differences compared to Ru foil and RuO₂, reflecting its unique coordination environment [Figure 12F]. Wavelet transform (WT) analysis of the EXAFS signal reveals only characteristic peaks, indicating the Ru atom possesses a distinctive coordination environment. WT analysis reveals that the EXAFS signal exhibits only a characteristic Ru-O shell peak at ~ 1.5 Å, with no Ru-Ru bond signal detected, further confirming the single-atom dispersion [Figure 12G]. The FT-EXAFS spectrum exhibits only a Ru-O peak at ~ 1.5 Å without a metallic Ru-Ru peak, validating the Ru-O coordination configuration [Figure 12H]. A schematic summarizes the precise positioning of the Ru SA: anchored atop the Fe atom by three oxygen atoms, forming a well-defined coordination microenvironment [Figure 12I]. This microenvironmental constraint (precise Ru-O-Fe coordination) stabilizes the hydrazine electrooxidation intermediates (*N₂H₃, *N₂H) while reducing the bandgap energy. Concurrently, the monolayer LDH structure and high specific surface area (~ 358 m² g^-1) optimize mass transfer between reactants and products. The synergistic effect of microenvironment confinement and enhanced mass transfer endows the Ru₁/mono NiFe catalyst with exceptional activity and stability.

Monolayer LDHs offer unique advantages for microenvironment regulation and mass transfer optimization, with heteroatom doping or single-atom anchoring further enhancing catalytic microenvironment modulation. Zeng et al. anchored Ce single atoms on monolayer NiV LDH (Ce SAs/m-NiV LDH) via vanadium vacancy trapping during hydrothermal synthesis, forming stable Ce-O-Ni coordination configurations^[114]. The monolayer structure reduces mass transfer resistance and exposes abundant active sites, while Ce single atoms narrow the LDH bandgap and strengthen density of states near the Fermi level, synergistically optimizing charge transfer and OH^- adsorption for OER. Wang et al. decorated non-precious Na single atoms on monolayer NiFe-LDH (Na/NiFe-LDH) via electrochemical insertion, constructing unique Na-O₃ coordination motifs on the LDH surface^[115]. The monolayer microenvironment facilitates rapid electrolyte diffusion, while Na single atoms induce spin-state inversion of Fe 3d orbitals by modulating Fe-O bond strength, optimizing OER intermediate adsorption kinetics without altering intrinsic Fe active sites.

Sun et al. constructed Ni SACs using organically intercalated LDH as a precursor^[63]. The intercalated microenvironment induces uniform dispersion of Ni active sites, while the hierarchical porous structure of carbon nanosheets enhances mass transfer, significantly improving 2e^- ORR performance and boosting a substantial increase in H₂O₂ yield. Liu et al. fabricated NiFe-LDH/Fe₁-N-C heterostructured hollow nanorods, where the hollow microenvironment reduced mass transfer resistance, while interfacial microenvironment regulation (electron transfer from LDH to Fe₁-N-C) optimized ORR/OER intermediate adsorption, achieving dual-function catalytic performance for ZABs^[96]. Focusing on ‘sesame ball’-like heterostructure design, Lu et al. anchored ultrasmall FeNi-LDH nanoparticles onto ZIF-8-derived FeNi-DACs^[62]. The porous carbon framework of DACs not only provides spatial confinement for LDH growth (inhibiting agglomeration and exposing more active sites) but also constructs a unique microenvironment through interfacial electronic coupling - transferring approximately 0.61 e^- from LDH to DACs modulates the d-band center of FeNi atom pairs, optimizing adsorption energy for ORR/OER intermediates. This architecture simultaneously addresses the insufficient conductivity of LDH and the weak OER activity of DACs. The porous structure shortens mass transport pathways and enhances charge transfer efficiency, enabling the catalyst to exhibit a peak power density of 211.6 mW cm^-2 and long-term cycling stability of 500 h in ZABs, significantly outperforming precious metal composite catalysts.

LDHs enable precise control over the microenvironment of active sites (e.g., coordination structure, defect distribution) via two-dimensional interlayer confinement, three-dimensional hollow confinement, or synergistic confinement - mass transfer strategies. Simultaneously, optimizing reactant/product diffusion efficiency enables synergistic enhancement of catalytic performance.

Two-dimensional interlayer confinement: Atomic-scale spatial constraints and microenvironment customization. Focusing on the two-dimensional confinement effect within LDH layers, atomic-scale constrained spaces are constructed via ion exchange or intercalation strategies to stabilize active sites and regulate reaction microenvironments. Chen et al. developed 5, 10, 15, 20-tetrakis(4-carboxyphenyl) porphyrin Co(II) (TCPP-Co) intercalated MgAl-LDH-supported Co SACs [Figure 13A]^[116]. The positively charged LDH layers stabilize negatively charged peroxymonosulfate (PMS) ions. The interlayer confinement space induces selective generation of surface-bound ·OH and SO₄·^- radicals, suppressing radical self-quenching and PMS decomposition while shortening the diffusion distance between pollutants and radicals. Co atom is anchored via Co-N₄ coordination. The two-dimensional confinement of LDH both fixes the active site and optimizes mass transfer efficiency, enabling efficient degradation of organic pollutants^[116]. Extending the concept of precise regulation through two-dimensional intercalation confinement, Fan et al. proposed a confinement synthesis strategy for LDH co-intercalated with organic molecules^[68]. Using CoAl-LDH as a precursor, they co-intercalated m-aminobenzoic acid (MA) and PA. MA provided N species to form Co-N active sites, while PA regulated pore structure to enhance active site exposure, while the two-dimensional interlayer confinement suppresses Co atom agglomeration, achieving uniform single-atom dispersion. Leveraging the advantages of flexible interlayer confinement in LDH, Yang et al. intercalated heme (Hm) between MgAl-LDH layers^[67]. High-temperature carbonization yielded the Fe-N-C catalyst (Hm-LDH-700). The two-dimensional interlayer space of LDH restricts heme aggregation. After carbonization, a graphene-like two-dimensional porous structure with a specific surface area of 1,065.79 m² g^-1 is formed. Hierarchical pore channels accelerate O₂ transport, uniformly dispersing Fe-N₄ active sites and significantly enhancing ORR catalytic performance. This represents an extended application of the two-dimensional confinement strategy. Interlayer confinement can be synergistically combined with LDH’s ‘memory effect’ to construct catalytic membranes, realizing convection-enhanced mass transfer for pollutant purification. Wang et al. embedded Fe single atoms into MgAl-LDH interlayers via the ‘memory effect’ (calcination-reconstruction) and fabricated a catalytic membrane (Fe_SA-in-LDH/M), with Fe single atoms stabilized as Fe-N₄ coordination configurations^[117]. The two-dimensional interlayer confinement enriches phenoxyl radicals and PMS intermediates, while the membrane’s flow-through mode compresses the diffusion boundary layer, achieving convection-enhanced mass transfer that promotes pollutant polymerization and separation.

Figure 13. (A) In layered double hydroxides, single-atom covalent sites can be activated by persulfate to selectively generate surface-bound free radicals that degrade EOCs. Reprinted with permission from Ref.^[116]. Copyright 2024, Elsevier; (B) Schematic illustration for the fabrication of Ru-SAC/NiFe LDH Reprinted with permission from Ref.^[46]. Copyright 2025, Wiley-VCH; (C) Schematic illustration of the synthesis route to NiFe-LDH@La@SNHPC. Reprinted with permission from Ref.^[61]. Copyright 2025, The Royal Society of Chemistry. 2D: Two-dimensional; 3D: three-dimensional; ROS: reactive oxygen species; PMS: peroxymonosulfate; LDH: layered double hydroxide; ZIF: zeolitic imidazolate framework; NHPC: N-doped hollow porous carbon; SNHPC: S/N co-doped hollow hierarchical porous carbon; EOC: emerging organic contaminant.

Three-Dimensional Hollow Confinement, Macro-Structural Design and Mass Transfer Optimization. Leveraging LDH’s topological transformation properties, a three-dimensional hollow structure was engineered. Spatial confinement stabilizes active sites while shortening mass transfer pathways and reducing diffusion resistance. Israr et al. synthesized Ru SACs supported on NiFe LDH hollow nanocages (Ru-SAC/NiFe LDH) via MIL-88A template etching-coprecipitation [Figure 13B]^[46]. The three-dimensional hollow nanocage provides abundant mesopores (~ 2.19 nm) and a large specific surface area (~ 157.5 m² g^-1). Ru atoms are anchored via Ru-O-M (M = Ni/Fe) bonds on cage surfaces. The hollow structure reduces reactant diffusion resistance, while electron transfer from Ni/Fe stabilizes Ru’s +3.7 oxidation state, synergistically enhancing OER kinetics.

Synergy of confinement and mass transfer, multidimensional regulation for synergistic enhancement. Integrating confinement regulation with mass transfer optimization through multi-level structural design achieves dual enhancement of microenvironment control and mass transfer efficiency. Yin et al. designed a nanoreactor [NiFe-LDH@La S/N co-doped hollow hierarchical porous carbon (SNHPC)] featuring hollow porous carbon loaded with La single atoms and NiFe-LDH nanoplates, corresponding to the structural concept in Figure 13C^[61]. The hollow cavities and multi-level channels of the carbon carrier enrich local OH^- concentration and enhance electrostatic field strength. La atoms are coordinatively anchored via La-N₄ bonds, forming a localized coexistence structure with NiFe-LDH nanoparticles. The confinement effect modulates electronic structure and lowers the OER rate-limiting step energy barrier, while the porous structure accelerates mass transfer at the gas-liquid-solid triple phase boundary. This catalyst achieves 350 h long-term cycling stability in ZABs. Focusing on a systematic summary of confinement mechanisms, Fan et al. provide a review that systematically outlines synthesis strategies for LDH-based confined SACs (spatial, coordination, and ionic confinement)^[110]. They clarify that confinement methods such as two-dimensional interlayer and three-dimensional hollow structures stabilize single atoms through size effects and electronic effects while optimizing mass transfer, providing theoretical support for the application of various confinement strategies.

Interfacial synergy engineering: enabling functional division of labor and relay catalysis

Interface design serves as a core strategy by which LDH supports enable the rational reconstruction of catalytic systems and unlock multifunctional catalytic performance. Single active sites are often inadequate to address the multi-step demands of complex reactions^[118-121]. By strategically constructing interfaces between LDHs and various active components (single atoms, clusters, etc.), interfacial synergy engineering creates systems where multiple sites cooperate through functional division of labor and relay catalysis. The approach modulates electronic interactions and local microenvironments at the interfaces, allowing distinct sites to specialize in specific reaction steps while working in concert to efficiently drive the overall process^[121,122]. This section elaborates on the design principles, mechanistic insights, and catalytic applications of such synergistic interfaces, revealing how this strategy expands the functional potential of LDH-based catalysts.

Using CoV-LDH as the catalyst support, a synergistic three-active-site system was constructed via Pt single-atom anchoring. Leveraging interfacial synergy engineering, functional division and relay catalysis were achieved in alkaline HER: water adsorption and decomposition → H₃O⁺ migration → H₂ generation. Li et al. designed Pt single-atom-anchored CoV-LDHs catalysts (Pt/CoV-LDHs)^[52]. They synthesized needle-like CoV-LDHs via hydrothermal synthesis, followed by electrochemical deposition to anchor Pt SAs on its surface. This formed triple active sites (V, Co, Pt) enabling a three-step relay reaction for alkaline HER.

The relay catalysis schematic clearly illustrates the functional division among the three active sites: the V site adsorbs water, the Co site synergistically decomposes water and migrates H, while the Pt site generates H₂ [Figure 14A]. Computational modeling of Pt/CoV-LDHs confirmed Pt SAs are anchored to the CoV-LDH surface via dioxygen coordination [Figure 14B]. Free energy calculations indicate that the V site (adjacent to an oxygen vacancy) exhibits the lowest water adsorption energy (-0.025 eV), making it the optimal water adsorption site [Figure 14C]. The water splitting energy barrier diagram reveals that the synergistic action of Co and V sites reduces the water splitting energy barrier to only 0.043 eV, making the reaction spontaneous [Figure 14D]. The hydrogen atom migration pathway from the Co site to the Pt site is also depicted [Figure 14E]. The energy diagram confirms the thermodynamic spontaneity of this migration process [Figure 14F]. Hydrogen adsorption energy calculations indicate that the Pt site exhibits an adsorption energy of -0.111 eV, close to the ideal value, making it the primary active site for H₂ formation, while the Co site primarily facilitates hydrogen migration [Figure 14G].

Figure 14. (A) Schematic design diagram for the tandem catalysis. (B) Computational model of designed Pt/CoV-LDHs; (C) The H₂O adsorption free energy at Pt site and V site on Pt/CoV-LDHs; (D) Water dissociation barrier on catalyst; (E) The migration path of hydrogen, and (F) corresponding energies diagram; (G) Calculated adsorption energies of H on Co1, Co2, and Pt sites. (A-G) Reprinted with permission from Ref.^[52]. Copyright 2024, Elsevier. LDH: Layered double hydroxide.

Experimental and theoretical validation demonstrates that the V site adsorbs and activates water via oxygen vacancies, while Co and V synergistically decompose water to form H₃O⁺. The Co site transfers H to the Pt site, where H₂ is rapidly generated via the Volmer-Tafel mechanism. In situ Raman spectroscopy confirms the presence of the H₃O⁺ intermediate, establishing a localized acid-like microenvironment that significantly enhances alkaline HER activity.

Using LDHs as catalyst supports, multi-active-site systems can be constructed via interfacial coordination engineering to achieve synergistic effects characterized by functional division and relay catalysis. These include synergy between metal single atoms and acidic sites, alternating synergy between single atoms and LDH supports, and bidirectionally stable synergy between single atoms and LDH-based active sites.

Focusing on the electronic regulation at the interface between LDH-derived carriers and single atoms, a metal-acid dual active site was constructed to achieve efficient relay of multi-step hydrogenation-deoxygenation (HDO) reactions through functional division of labor. Wei et al. used CoAl-LDH as a precursor to prepare a Co₂AlO₄-supported Pt SAC (0.4%Pt/Co₂AlO₄) via a topological transformation^[123]. They achieved synergistic interaction between Pt SAs and Brønsted acid sites on the carrier surface through interfacial engineering: Pt SAs activate adsorbed 5-hydroxymethylbenzene, while Brønsted acid sites facilitate its oxidation. Through interfacial engineering, Wei et al.^[123] achieved synergistic interaction between Pt SAs and Brønsted acid sites on the support surface; Pt atoms activate the C=O bond of adsorbed 5-hydroxymethylfurfural (5-HMF), lowering the energy barrier for the RDS of C-OH bond cleavage, while Brønsted acid sites accelerate the second-step C-OH bond dissociation. This relay mechanism completes the HDO reaction, enabling efficient synthesis of 2,5-dimethylfuran (DMF). This functional division between metal and acid sites exemplifies the application of interfacial synergistic engineering in multi-step organic transformations.

By leveraging the interlayer confinement effect of LDH to anchor single atoms, an alternating synergistic system of single atoms and LDH carriers was constructed. Functional division between HER and OER enhanced overall water splitting performance. Chen et al. employed an anion exchange-spatial confinement strategy to embed Pt SAs into the interlayer of Ni₃Fe-LDH (Ni₃Fe-CO₃^2--LDH-Pt SA), revealing an alternating synergistic mechanism of ‘single-atom-empowered carrier + carrier-assisted single atom’^[48]. HER polarization curves demonstrate that this catalyst achieves 10 mA cm^-2 at just 45 mV overpotential, outperforming commercial 20 wt.% Pt/C, clearly illustrating the synergistic enhancement effect between Pt SACs and LDH [Figure 15A]. This enhancement stems from dual effects: Pt SACs significantly boost LDH’s electron transport capacity, while Ni₃Fe-LDH accelerates water dissociation, enabling HER to follow a hybrid Heyrovsky-Volmer/Tafel-Volmer mechanism [Figure 15B]. Schematic diagrams clearly illustrate the functional division between single atoms as active sites and LDH as a synergistic carrier [Figure 15C]. For the OER, Pt SACs not only promote the transformation of Ni₃Fe-LDH into the active phase Ni^2+δFe^3+ζO_xH_y, but also optimize its intrinsic activity. The OER polarization curve reveals an overpotential of only 218 mV at 10 mA cm^-2 [Figure 15D]. The mechanism of promoting phase transformation is clarified by schematic diagrams, Pt SACs reduce the phase transition energy barrier by modulating the Ni electron density [Figure 15E]. Differential charge density maps further validate the electronic interaction between Pt and Ni/Fe-O bonds [Figure 15F]. Bidirectionally stable synergy between SACs and LDHs enables active site protection and enhances OER performance.

Figure 15. (A) HER polarization curves in 1 M KOH; (B) Schematic representations of HER mechanism for Pt/C in 1 M KOH and (C) Ni₃Fe - CO₃^2- LDH-Pt SA in 1 M KOH; (D) OER polarization curves for Ni₃Fe - CO₃^2- LDH and Ni₃Fe - CO₃^2- LDH-Pt SA. (E) Schematic of promotion effect on active phase transition for Pt single - atom in Ni₃Fe - CO₃^2- LDH; (F) Differential charge densities of Ni₃Fe - CO₃^2- LDH-Pt SA. (A-F) Reprinted with permission from Ref.^[48]. Copyright 2021, The Royal Society of Chemistry. LDH: Layered double hydroxide; RDS: rate-determining step; HER: hydrogen evolution reaction; OER: oxygen evolution reaction; SA: single atom.

The bidirectional synergistic logic of interface coordination enables mutual stabilization between the single atom and LDH active sites, achieving simultaneous enhancement of catalytic activity and stability. Cao et al. prepared an Ir single-atom-doped CoFe-LDH/rGO catalyst (Ir/CoFe-LDH/rGO) via a hydrothermal-impregnation method^[44]. They discovered a bidirectional synergistic effect between Ir SACs and CoFe-LDH, LDH modulates Ir’s electronic state via Ir-O-M (M = Co/Fe) coordination bonds, enhancing its OER activity. Conversely, Ir single atoms stabilize Fe active sites on LDH through two mechanisms: Fe sites adjacent to Ir exhibit reduced activity and enhanced stability due to electronic coupling with Ir, while distant Fe sites experience decreased local OH^- concentration caused by Ir’s rapid consumption of OH^-, thereby minimizing Fe dissolution and phase transitions. This achieves bidirectional stabilizing synergy between ‘active sites and carrier’, refining the bidirectional enabling mechanism of interfacial synergy.

Dynamic phase engineering: directing in situ reconstruction toward active phases

Dynamic phase engineering represents an advanced paradigm for catalyst design that goes beyond static active-site optimization. This strategy specifically employs LDH supports to direct and regulate the in situ reconstruction of the matrix under catalytic operating conditions. Through targeted doping with single atoms or heteroatoms, the inherent phase transformation of LDHs into more active (oxy)hydroxide phases (e.g., NiFeOOH, FeNiOOH) is not merely allowed but precisely steered^[124,125]. The core mechanism hinges on the dopants modulating the host’s electronic structure and lowering the energy barrier for phase transition. This deliberate intervention optimizes the adsorption strength of reaction intermediates on the newly formed active phase, thereby synergistically enhancing both catalytic activity and operational stability.

Focusing on single atoms as ‘phase-transition catalysts’ that guide the in situ reconstruction of LDH into the active NiFeOOH phase, Zhang et al. synthesized single-atom Au-doped NiFe LDH (sAu/NiFe LDH) via a simple strategy, revealing the core mechanism of single-atom-induced dynamic LDH restructuring^[126]. They discovered that LDH does not retain its original structure during the OER process. Instead, it undergoes irreversible in situ restructuring induced by single-atom Au, forming a stable NiFeOOH active phase [Figure 16A]. During this reconstruction, the Au atom bonds to LDH via an Au-O bond, transferring 0.32 e^- to the Fe active site and surrounding atoms. This regulates charge distribution and optimizes the adsorption energies of OER intermediates (OH*, O*, OOH*) [Figure 16B]. Free energy calculations indicate that the overpotential for the RDS (O* → OOH*) on the reconstructed sAu/NiFeOOH-NiFe LDH is only 0.18 V, significantly lower than that of the unreconstructed NiFe LDH (0.26 V). Experimentally, this catalyst exhibits an overpotential of 237 mV at 10 mA cm^-2, demonstrating a sixfold increase in activity with no significant decay after 2,000 cycles [Figure 16C].

Figure 16. (A) Two-layer slab model for sAu/NiFe LDH with interlayer CO₃^2- anions and water molecules; (B) Proposed OER pathways with OH*, O* and OOH* intermediates for sAu/NiFe LDH; (C) Free energy diagram for the OER at different potentials on the surface of sAu/NiFe LDH model. (A-C) Reprinted with permission from Ref.^[126]. Copyright 2018, American Chemical Society. LDH: Layered double hydroxide; OER: oxygen evolution reaction; sAu/NiFe LDH: single-atom Au-doped NiFe LDH.

Single-Atom Ir-Induced LDH Reconfiguration, Directional Formation of Active Sites and Carrier Activation. Building upon the logic of single-atom-induced reconfiguration, Li et al. employed an in situ electrostatic adsorption anchoring strategy to load Ir single atoms onto NiFe LDH (Ir/NiFe LDH)^[127]. They discovered that the Ir SACs (with a +5.5 oxidation state) bind to LDH via Ir-O bonds, not only activating the inert LDH carrier but also guiding LDH to undergo in situ reconstruction into the Ni^2+δFe^3+ζO_xH_y active phase during the OER process. During this reconstruction, bidirectional electron transfer occurs between Ir and Ni/Fe, shifting Ni’s binding energy positively and Fe’s negatively. This optimizes the d-band center and lowers the energy barrier of the RDS in OER. In situ Raman spectroscopy confirms the formation of the active phase. X-ray absorption spectroscopy (XAS) and TEM characterization reveal uniform dispersion of Ir single atoms without agglomeration or detachment post-reaction, with strong metal-carrier interactions ensuring the stability of the reconstruction process.

Ru-Doped-Induced LDH Reconfiguration, Mechanism regulation of SACs vs. Double-Doped Reconfiguration. To optimize reconfiguration for multi-reaction scenarios, Xu et al. prepared single-atom Ru-doped NiFe LDH (Ru_0.3/NiFe) via two-step electrodeposition^[49]. They found that introducing Ru SAs guided LDH reconfiguration into the active FeNiOOH phase. Ru atoms bind to LDH via Ru-O-M (M = Ni/Fe) bonds, facilitating electron transfer from Ni to Ru and electron accumulation from O to Ru, thereby optimizing the adsorption energy of HMF oxidation intermediates. XAS characterization confirms Ru exists in the +2.7 oxidation state, atomically dispersed in a RuO₄ structure, while Raman spectroscopy verifies the transformation of LDH into the active NiOOH phase during reaction. DFT calculations indicate that Ru introduction reduces Ni dehydrogenation free energy, promoting Ni(OH)₂ conversion to NiOOH while enhancing HMF-catalyst surface interactions to accelerate reaction pathways. Extending the strategy of dual-doping-induced reconstruction, Zhu et al. designed Ru single-atom and S anion dual-doped NiFe LDH (Ru-S-NiFe LDH)^[128]. They discovered that the S anion accelerates the reconstruction of LDH into the active NiFeOOH phase by modulating lattice parameters and electron distribution, thereby lowering the reconstruction energy barrier. The Ru SA, dispersed in Ru-O/S coordination forms, optimizes the electronic structure of the active phase through electron transfer while mitigating Ru’s excessive oxidation. Operando XAS characterization revealed that the valence states of Ru and Ni increased with rising reaction potential, while Fe showed no significant change, confirming Ru and Ni as primary active sites with Fe primarily contributing structural stability. DFT calculations validated that dual doping synergistically reduces the adsorption energy difference of OER intermediates, optimizing reaction kinetics.

Reaction-pathway engineering: switching mechanisms for performance breakthrough

Reaction-pathway engineering represents a transformative strategy that extends beyond tuning individual active sites to actively reprogram the reaction network itself. By utilizing LDHs as a dynamic catalytic platform, this approach takes advantage of their structural and electronic versatility to direct and switch catalytic mechanisms. By strategic modifications such as single-atom doping, defect creation, or topological transformation, the intrinsic scaling relationships and thermodynamic limitations of conventional pathways can be circumvented^[129,130]. The key lies in the ability of LDHs - through their tunable composition, confinement effects, and strong interfacial interactions - to precisely modulate intermediate adsorption energies, alter charge transfer routes, and even activate lattice oxygen species. This capacity enables a deliberate shift from one dominant mechanism to another (e.g., from adsorbate evolution to lattice oxygen oxidation in OER, or from partial to deep hydrogenation), providing a fundamental driving force for breakthroughs in catalytic selectivity and efficiency.

OER remains the kinetic bottleneck of water splitting, with traditional mechanisms facing inherent trade-offs: the adsorbate evolution mechanism (AEM) is constrained by the linear scaling relationship of intermediate adsorption energies, while the lattice oxygen mechanism (LOM) - though capable of overcoming this scaling limitation - often suffers from structural instability. LDHs paired with single-atom engineering address this dual challenge, leveraging LDH’s structural flexibility and electronic tunability to enable OER pathway switching (AEM-to-LOM) or dual-pathway synergy, while inducing directional active site remodeling that balances catalytic kinetics and structural robustness. Wang et al. synthesized high-entropy MnFeCoNiCu LDH modified with Au SAs and oxygen vacancies, where the synergistic effect of Au SAs and vacancies weakens Ni-O bonds to direct OER pathway conversion from AEM to LOM^[131]. This modulation reconstructs Ni sites into the core active centers of LOM, circumventing AEM’s intrinsic scaling limitation. Figure 17A presents the pH dependence of OER activity [ρRHE (the proton reaction orders on reversible hydrogen electrode scale) = 0.89] derived from linear sweep voltammetry (LSV) tests, which is significantly higher than that of pure high-entropy LDH (0.36), providing direct evidence for non-proton-coupled electron transfer-dominated LOM characteristics. Figure 17B and C demonstrate a notable overpotential at a current density of 100 mA cm^-2 (Δη₁₀₀ = 0.102 V) in tetramethylammonium hydroxide (TMAOH) electrolyte, as TMA⁺ strongly binds to O₂^2- intermediates generated via LOM, hindering the reaction process and further validating LOM dominance. In situ Raman spectroscopy detects the O₂^2- stretching vibration peak at 1,089 cm^-1, and ¹⁸O isotope labeling experiments verify extensive lattice oxygen participation in O₂ generation, solidifying the AEM-to-LOM pathway shift [Figure 17D-F].

Figure 17. (A) LSV curves in KOH and log j vs. pH plot at 1.45 V vs. RHE for proton reaction order; (B) Polarization curves of Au_SA-MnFeCoNiCu LDH and MnFeCoNiCu LDH in 1.0 M KOH/TMAOH, with corresponding Δη₁₀₀ and Tafel slope variations; (C) Raman spectra of Au_SA-MnFeCoNiCu LDH and MnFeCoNiCu LDH after 30 min electrolysis at 1.45 V vs. RHE in 1.0 M KOH/TMAOH; (D) In situ Raman spectra of MnFeCoNiCu LDH; (E) In situ Raman spectra of Au_SA-MnFeCoNiCu LDH; (F) ¹⁸O isotope-labeling mass spectra; (G) Adsorbate evolution mechanism and lattice oxygen oxidation mechanism on MnFeCoNiCuOOH. (A-G) Reprinted with permission from Ref.^[131]. Copyright 2023, Springer Nature. AEM: Adsorbate evolution mechanism; LOM: lattice oxygen mechanism; LSV: linear sweep voltammetry; SA: single atom; RHE: reversible hydrogen electrode; Δη₁₀₀: refers to the overpotential at a current density of 100 mA cm^-2.

Wang et al. synthesized cerium-substituted NiFe-LDH (NiFe-Ce LDH)^[132]. Ce single-atom doping modulates NiFe LDH via Ce 4f-O 2p electronic interaction, which shifts the O 2p band center upward to controllably activate local LOM while retaining AEM, forming a synergistic dual reaction pathway. LDH’s interlayer structure stabilizes the in situ reconstructed NiOOH active layer, and in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and Raman spectroscopy separately detect *OOH (AEM-specific) and OO* (LOM-specific) intermediates, with Fe sites stabilized by Ce-induced electronic regulation. This dual-pathway design integrates the kinetic advantage of LOM and the stability of AEM, realizing balanced catalytic performance. Duan et al. precisely anchored Ir single atoms to the Fe sites of NiFe LDH, forming a distinct Ir-O-Fe coordination configuration^[133]. This configuration enhances metal-oxygen covalent interaction and shifts the O 2p band center upward, enabling complete AEM-to-LOM conversion that avoids the high-energy *OOH intermediate. LDH serves as a stable anchoring platform for Ir single atoms and induces remodeling of active sites into Ir-O-Fe/γ-NiOOH composite centers, where the synergistic interaction between Ir single atoms and LDH-derived γ-NiOOH further optimizes catalytic dynamics.

Single-atom charge density modulation: Pathway-selective switching in HDO reactions. Dai et al. successfully synthesized two Pt SACs - Pt₁/NiAl-LDH and Pt₁/NiAl-IMC - using NiAl-LDH as a precursor via an anion intercalation-two-dimensional confinement thermal reduction strategy^[60]. PtCl₆^2- intercalated between LDH layers is confined by electrostatic interactions. After low-temperature reduction at 200 °C, the LDH support structure is retained, with Pt SAs existing in a Pt-O_x coordination state and an electron-deficient state. High-temperature reduction at 400 °C induces a topological transformation of LDH into NiAl intermetallic compounds (IMC), where Pt atoms form Pt-Ni_x coordination and exhibit an electron-rich state [Figure 18A]. This charge density difference directly switches the HDO pathway of 4-propylguaiacol, electron-deficient Pt sites enhance C=O bond adsorption while inhibiting C-OH bond cleavage, favoring selective HDO to yield 4-propylguaiacol Propylcyclohexanol. Electron-rich Pt sites inject electrons into the C-O bond to weaken its bond energy, shifting the pathway toward deep deoxygenation to form propylcyclohexane. This achieves precise control over product selectivity. By modifying the support structure to finely regulate the local charge density of platinum SACs, the product selectivity of the lignin hydrodeoxygenation reaction can be tuned^[60].

Figure 18. (A) Schematic illustration of the confinement strategy to synthesize Pt₁/NiAl-LDH and Pt₁/NiAl-IMC catalysts. Reprinted with permission from Ref.^[60]. Copyright 2025, Wiley-VCH; (B) Schematic illustration of the fabrication of the catalysts and the main products of CO photo-hydrogenation. Reprinted with permission from Ref.^[65]. Copyright 2023, Springer Nature. LDH: Layered double hydroxide; IMC: intermetallic compound; NP: nanoparticle; NA: nanoalloy; SAA: single-atom alloy.

By leveraging the topological transformation properties of LDH to construct SAA systems, the competition between C-C coupling and over-hydrogenation in CO hydrogenation is regulated, enabling the switching of reaction pathways to produce either short-chain hydrocarbons or long-chain liquid fuels. Zhao et al. synthesized the Ru₁CoAl-LDH precursor via a one-step hydrothermal method^[65]. Hydrogen reduction at 650°C induced the LDH topological transition, yielding an aluminum oxide-supported ruthenium-cobalt SAA catalyst (Ru₁Co-SAA) [Figure 18B]. The layered structure of LDH provides confined space for atomically dispersed Ru and Co. After reduction, Ru atoms replace Co lattice sites to form a Ru-Co coordinated SAA structure without Ru-Ru agglomeration. This unique structure alters the reaction pathway for CO photohydrogenation. The single-atom Ru sites enhance CO dissociative adsorption and lower the C-C coupling energy barrier, while the Co sites suppress excessive hydrogenation of CH_x intermediates to methane, thereby synergistically promoting the formation of highly unsaturated C₂ intermediates. This significantly increases the probability of carbon chain growth, enabling the catalyst to efficiently produce C₅⁺ liquid fuels near atmospheric pressure (0.1 ~ 0.5 MPa). This breakthrough overcomes the limitation of traditional Fischer-Tropsch synthesis (FTS) requiring high pressure to promote long-chain formation.

Versatile functional expansion: beyond catalysis via the LDH ‘atomic canvas’

The ‘atomic canvas’ essence of LDHs transcends mere catalytic interface reconstruction, leveraging their inherently tunable layered architecture, flexible topological transformation capabilities, and controllable interfacial interactions to drive functional expansion into a diverse array of fields. Beyond traditional electrocatalysis, this platform has penetrated nanozymes, organic synthesis, electrochemical conversion, environmental remediation, plastic waste upcycling, and biomedical applications^[134-142]. Through atomically precise engineering - including single-atom/nanoparticle synergistic anchoring, interlayer molecule intercalation, defect modulation, and topological derivation - LDHs act as versatile carriers, structural precursors, or active components. They enable multifunctional capabilities ranging from radical scavenging and biomass valorization to selective chemical bond formation, pollutant abatement, cyclic alcohol/ketone synthesis, and antitumor/antibacterial therapies. This broad applicability stems from LDHs’ core advantage of ‘structurally designable-functionally customizable’, allowing targeted regulation of active-site structure and electronic environment to address field-specific challenges via tailored structural engineering.

LDHs serve as a versatile platform for multi-scenario functional extension, enabling precise regulation of active-site structure and electronic environment via component doping, topological transformation, synergistic loading of single atoms or nanoparticles, and organic molecule intercalation. This platform extends to diverse fields including CO₂ electroreduction, biocatalysis, energy storage, and multi-pathway electrocatalysis, addressing field-specific challenges via targeted structural engineering and electronic regulation.

For CO₂ electroreduction, Zhang et al. developed a novel, straightforward method for preparing SACs for Electrochemical carbon dioxide reduction reaction (CO₂RR) by utilizing NiZn-LDHs as the metal source^[143]. NiZn-LDH serves as a Ni source and structural template, polyhydroxy compound-induced monolayer exfoliation mitigates Ni atom aggregation during calcination, while Zn volatilization constructs mesoporous architectures to ensure uniform active site dispersion and facilitated mass transport. Topological transformation of LDH enables synergistic loading of Ni single atoms and nanoparticles. Ni nanoparticles promote H₂O dissociation to generate H* and reduce the energy barrier for *COOH formation, while Ni SAC accelerates CO desorption, balancing proton supply and hydrogenation kinetics. Self-supporting nanoarrays derived from LDH topological transformation anchor atomically dispersed active sites uniformly, enhancing electron conduction efficiency and shortening CO₂ diffusion pathways to adapt to high-current-density reaction requirements. Integrating CO₂ capture with in situ conversion expands the application of the LDH ‘canvas’ in resource recycling. Gao et al. fabricated thickness-tunable Pt/MgFe-LDHs by capturing atmospheric CO₂ as interlayer CO₃^2-, constructing Pt^δ+-V_o-Fe²⁺ interfacial sites via Pt single-atom anchoring on oxygen vacancies^[144]. This design realizes photocatalytic coupling of CO₃^2- reduction (to CO/CH₄) and glycerol oxidation (to dihydroxyacetone/lactic acid), achieving simultaneous utilization of low-valued CO₂ and biomass derivatives.

In the realm of biocatalysis (nanozymes), LDHs capitalize on biocompatibility and single-atom anchoring capability to construct nanozyme systems. Liu et al. synthesized a ruthenium single-atom nanozyme (SAE) characterized by atomically dispersed ruthenium atoms on a biocompatible magnesium-aluminum LDH (Ru₁/LDH)^[56]. The prepared Ru₁/LDH SAE exhibits high intrinsic peroxidase (POD)-like catalytic activity, with performance 20 times that of Ru nanocluster (NC) nanoenzymes. This nanozyme, possessing both POD and superoxide dismutase (SOD) activities, mediates the heterolytic cleavage of hydrogen peroxide (H₂O₂) (free energy: 0.43 eV), thereby efficiently scavenging superoxide anion (O₂^-·) and hydroxyl radical (·OH). Optimization of the single-atom coordination environment (e.g., Ru-O₃ configuration on MgAl-LDH) enhances nanozyme catalytic efficiency and cycling stability, enabling continuous free radical scavenging over multiple cycles while sustaining long-term antioxidant effects in cellular environments [Figure 19A]. To investigate the intracellular antioxidant activity of Ru₁/LDH, 2’,7’-dichlorofluorescein (DCFH-DA) was employed as a fluorescent probe to detect reactive oxygen species levels. RAW264.7 cells (mouse monocyte-macrophage leukaemia cells) exhibited elevated fluorescence signals after 12 h of Rosup stimulation. Following the addition of LDH or Ru₁/LDH, fluorescence intensity decreased. Notably, the fluorescence signal exhibited a marked reduction for Ru₁/LDH. Flow cytometric quantification revealed that nearly 83% of reactive oxygen species (ROS) could be effectively eliminated. This demonstrates that Ru₁/LDH efficiently scavenges intracellular ROS, thereby protecting cells from oxidative stress [Figure 19B].

Figure 19. (A) Biocompatible MgAl-LDH-supported Ru single-atom nanozyme with multi-enzyme mimetic activity and high intrinsic peroxidase-like activity; (B) ROS-scavenging in RAW 264.7 cells by Ru₁/LDH and LDH. (A and B) Reprinted with permission from Ref.^[56]. Copyright 2023, Wiley-VCH; (C) Optimized atomic configurations of ORR/OER elementary steps on FeNi-LDH@DACs; (D) Top/side views of FeNi-LDH@DACs charge density difference; (E) Electron density map of FeNi-LDH@DACs; (F) Structures and charge transfer directions of FeNi-LDH@DACs and FeNi-DACs; (G) Schematic of liquid Zn-air batteries; (H) Discharge-charge cycling of FeNi-LDH@DACs and 20% Pt/C + RuO₂ in liquid ZABs. (C-H) Reprinted with permission from Ref.^[62]. Copyright 2025, American Chemical Society. SOD: Superoxide dismutase; CAT: catalase; DPPH: 1,1-diphenyl-2-picrylhydrazyl radical; LDH: layered double hydroxide; DAC: dual-atomic catalyst; PCD: peroxidase; ROS: reactive oxygen species; ORR: oxygen reduction reaction; OER: oxygen evolution reaction; ZAB: zinc-air battery.

Expanding the biomedical potential of LDH-based single-atom systems, multi-functional nanozymes and sonosensitizers are innovatively developed. Wang et al. constructed DT-ZnFe-LDH@Cu by anchoring Cu single-atom nanozymes on ZnFe-LDH and modifying with aminated dextran, endowing it with POD, oxidase, and catalase-like activities for bacterial keratitis treatment^[145]. The Cu-N coordination sites generate reactive oxygen species to eradicate biofilm-embedded bacteria, while surface modification facilitates biofilm penetration and macrophage polarization from M1 to M2 to alleviate inflammation. Wang et al. coupled Pt SAs with amorphous CoMgMo-LDH to fabricate a sonosensitizer (Pt/a-LDH), leveraging defect-single atom synergy to narrow the bandgap and suppress electron-hole recombination^[146]. The Pt-O coordination sites enhance oxygen adsorption/activation, promoting singlet oxygen generation for sonodynamic therapy and inducing immunogenic cell death to trigger anti-tumor immune responses.

Extending LDH-based single-atom systems to environmental remediation, nonradical catalytic pathways are innovatively developed. Wang et al. constructed a Fe single-atom modified LDH membrane (Fe-LDH) that activates PMS via a surface-bound PMS intermediate-driven electron transfer pathway^[147]. The Fe-N₄ coordination sites on LDH induce phenolic pollutant polymerization, leveraging nanochannel confinement to enhance reactant proximity and phenoxyl radical enrichment for efficient water purification. Ma et al. derived a Pt single-atom/Cu NC synergistic catalyst from NiFeCu-LDH precursors, where Pt SAs (Pt-N coordination) enhance methyl mercaptan (CH₃SH) adsorption and Cu NCs activate O₂^[148]. This Langmuir-Hinshelwood mechanism-driven system achieves efficient CH₃SH oxidation, expanding LDH’s application in volatile sulfur compound abatement.

Advancing plastic waste upcycling and aromatic hydrogenation, LDH-based single/dual-atom catalysts enable selective conversion to high-value cyclic alcohols/ketones. Liu et al. anchored Pd single atoms on calcined MgAl-LDH (Pd/CHT-800) to form Pd-O-MgAl active sites, realizing selective hydrogenation of phenols to cyclohexanones in aqueous media^[149]. The electron-deficient Pd single atoms activate benzene rings while the LDH’s surface basicity inhibits carbonyl group adsorption, avoiding over-hydrogenation to cyclohexanols. Wang et al. developed a RuLa dual-atom catalyst from La-doped CoAl-LDH precursors via anion intercalation and thermal reduction, constructing isolated Ru-La atomic pairs on CoAl oxide^[150]. This catalyst mediates tandem hydropyrolysis-hydrogenation of polycarbonate waste, preserving intrinsic oxygen functionalities to produce cyclohexanol via non-oxidative pathways, with Ru activating H₂ and La facilitating hydrogen spillover.

Using LDHs as electrode substrates, the OER/ORR bifunctional catalytic performance can be optimized via single-atom loading, defect engineering, or heterogeneous coupling, meeting the requirements of energy storage devices such as ZABs. By employing defective LDHs as an electronic modulation platform, single atoms can be anchored to tailor the electron distribution and boost reaction activity. For example, Hu et al. developed a defect-type nickel-iron LDH catalyst anchored by Ru SAs (Ru SAs/D-NiFe LDH@NF)^[41]. This material was synthesized via a hydrothermal reaction combined with an alkaline etching strategy. Cation vacancies generated by the alkaline etching anchored atomically dispersed Ru SAs, forming a stable and highly active catalytic interface. The Ru SAs transfer electrons to the LDH, optimizing the formation of an energy barrier (1.60 eV) at *OOH. By coupling LDH with SAC, synergistic active sites can be constructed on a ‘composite canvas’, improving the bifunctional catalytic performance of ZABs. Wang et al. synthesized a bifunctional catalyst by using atomically dispersed FeCo-NC materials with a three-dimensional floral morphology as a unique substrate for the controlled deposition of ultrafine NiFe LDH nanodots (NiFe-NDs)^[97]. The LDH nanoparticles provide highly active OER sites, while the iron-cobalt-nitrogen-carbon (FeCo-NC) nanoflowers optimize ORR kinetics. The interfacial coupling between the two accelerates charge transfer, achieving a balance between activity and stability.

Using LDH as a structural template, hierarchical porous bifunctional electrodes can be constructed to balance the catalytic activity and mass transfer efficiency in ZABs. Qin et al. proposed a novel interface-coupled ‘sesame ball’ catalyst, featuring FeNi-LDH nanoparticles densely grown on porous, conductive FeNi-DAC^[62]. This structure leverages potent synergistic effects to optimize intermediate adsorption, reduce activation energy, and enhance electron transfer, thereby achieving stable bifunctional ORR/OER performance. Within the FeNi-LDH@DACs composite structure, the tight interfacial coupling between LDH nanodots and the FeNi diatomic catalyst enables significant charge redistribution. This interfacial charge transfer effectively modulates the d-band centers of Fe and Ni active atoms, bringing their adsorption strengths for oxygen intermediates (*OOH, *OH) closer to the optimal range defined by the Sabatier principle. Consequently, ORR kinetics are enhanced by lowering the energy barrier for *OOH formation and accelerating electron transfer. In this system, spontaneous interfacial electron redistribution substantially boosts charge transfer and intrinsic ORR activity. Overall, strong electronic coupling at the LDH-DAC interface coordinates the favorable electronic structures of active FeNi sites, thereby improving ORR catalytic performance [Figure 19C-F]. The battery achieves a discharge voltage of 1.35 V and a charging voltage of 1.58 V at 10 mA cm^-2, with an energy efficiency of 85%, and exhibits stable operation for 500 h without significant performance degradation [Figure 19G].

As a versatile platform for the molecular-level control of multi-pathway ORR catalysis, Sun et al. synthesized a hierarchical carbon nanosheet array electrode with single-atom nickel sites (Ni-SAC) via calcination and etching of Mn-doped NiAl-LDH intercalated with m-diaminobenzenesulfonic acid (MA). MA tailors the microenvironment to promote the selective adsorption of O₂ and H* generation by Ni single atoms, enabling 2e^- ORR for H₂O₂ production^[63].

Single atoms synergize with Lewis acid sites to achieve highly selective lignin depolymerization. Meng et al. prepared the Mo₁Al/MgO catalyst by interlayer confinement anchoring MoO₄^2- using MgAl-LDH as a precursor, followed by thermal reduction^[151]. This catalyst features coexisting Mo₁-O₅ single atoms and Al Lewis acid sites. The two-dimensional confinement effect of LDH suppresses Mo species agglomeration. The Al Lewis acid sites formed after calcination synergize with Mo single atoms to selectively cleave the β-aromatic ether bond in lignin under an inert atmosphere. Methanol solvent participates in the reaction process: Mo₁-O₅ single atoms activate ether bonds, while Al Lewis acid sites stabilize reaction intermediates. This ultimately yields monophenolic products containing C_α = C_β double bonds with high selectivity, achieving yields close to theoretical values.

Topological transformation constructs SAAs, enabling highly selective anti-Marsch hydrogenation. Ma et al. used ZnAl-LDH as a precursor, undergoing thermal reduction-induced topological transformation to obtain Pt SACs supported on Zn(Al)O^[152]. The topological transformation of LDH provides stable anchoring sites for Pt atoms, enabling coexistence of Pt₁⁰ and Pt₁^δ+ species by regulating Pt loading. These two Pt species form a synergistic catalytic system: Pt₁⁰ activates the N-H bond of amines to render it electrophilic, while Pt₁^δ+ activates the C=C bond of alkenes via π-bonding to make the β-C nucleophilic. The nucleophilic β-C attacks the electrophilic amine, achieving anti-Marcy addition highly selectively (up to 92%) forming the C-N bond.

Lattice confinement engineering in LDHs enables precise modulation of single-atom dispersion and electronic state for thermal catalysis. Ma et al. developed pseudo-single-atom Pt catalysts by confining Sn/Zr promoters in LDH brucite-like lattices, where lattice confinement induces electron-rich (Sn) or electron-defected (Zr) sites to guide selective Pt dispersion^[153]. This strategy modulates Pt’s electronic properties for n-hexane reforming, realizing controlled formation of single atoms and sub-nanometer clusters without aggregation.

In summary, LDH’s ‘atomic canvas’ nature enables versatile functional expansion across electrocatalysis, biocatalysis, environmental remediation, plastic upcycling, biomedicine, and organic synthesis. Via atomically precise engineering (single-atom loading, intercalation, defect modulation, topological transformation), LDHs tailor active-site structure and electronic state to address field-specific demands. Their ‘structurally designable-functionally customizable’ advantage underpins synergistic enhancements between the canvas and anchored species. Table 1 summarizes recent advances in LDH-based SACs, including synthesis methods, single-atom loadings, bonding modes, and application fields. These advancements establish LDHs as a cross-disciplinary platform for high-performance multifunctional materials.