3D-printed hydrogel and joule-heating synthesis of Pt single-atom and nanoparticle electrodes for HER

Electrocatalysts for the hydrogen evolution reaction (HER) are critical for sustainable hydrogen production, yet simultaneously achieving high activity, atom-efficient noble-metal use and integrated fabrication remains challenging. Herein, we report a scalable strategy for fabricating integrated electrodes by combining 3D-printed hydrogel templating with ultrafast pulsed Joule heating. In detail, a 3D-printed hydrogel scaffold is transformed into an oxygen-functional hierarchical carbon support that anchors oxygen-coordinated Pt single atoms (SAs) with finely dispersed Pt nanoparticles (NPs). The resulting integrated SA/NP hybrid electrode exhibits greatly increased surface area and a micro-mesoporous architecture, which suppresses NP agglomeration, increases active-site density and improves charge transfer. First-principles calculations reveal that Pt NP primarily drives water dissociation and H* generation, while adjacent Pt SA enhances the active-site utilization of Pt NP and facilitates OH* transfer, together accelerating the HER pathway. As a result, the fabricated electrode delivers low overpotentials of 33, 103, and 173 mV at current densities of 10, 50, and 100 mA cm^-2, respectively, while also demonstrating remarkable durability. Beyond providing a practical route to atom-efficient HER electrodes, this integrated strategy uniquely combines a 3D-printed topological scaffold with ultrafast Joule heating to achieve synergistic Pt SA/NP sites, significantly enhancing both structural stability and catalytic kinetics, offering a great promise for next-generation energy-catalysis technologies.