fig13

Figure 13. (A) Ratio of Co²⁺: Co³⁺ in Co₃O₄ and 4% Er-Co₃O₄; (B) LSV curves of different catalysts at 1 mV/s scan rate and negative scan after iR correction; (C) Microkinetic OER activity volcano model at 10 mA cm^-2 as a function of GO-GHO. This figure is quoted with permission from Pan et al.^[122]; (D) The in situ Raman spectra of NiFe-LDH@NF and (E) Er-NiFe-LDH@NF for OER in 0.1 M KOH solution; (F) Comparison of the OER activity of catalysts’ polarization curves in 1.0 M KOH solution. This figure is quoted with permission from Zhu et al.^[123]. RHE: Reversible hydrogen electrode; LSV: linear sweep voltammetry; iR: internal resistance; OER: oxygen evolution reaction; GO-GHO: the difference between the Gibbs free energy of O* and OH*; LDH: layered double hydroxide; NF: nickel foam.