Lattice strain and atomic replacement of CoO₆ octahedra in layered sodium cobalt oxide for boosted water oxidation electrocatalysis

Layered alkali metal oxides have been emerged as an alternative group of low-cost and promising electrocatalysts in water oxidation. The distinct layered configuration may offer some interesting possibilities to tune the intrinsic activity by regulating the intralayer edge-shared CoO₆ octahedra and the CoO₂ interlayer spacing/strain. In this work, electrochemical desodiation tuning method is explored on intralayer Ag, Cu, Ce-doped Na_0.7CoO₂ for highly active OER catalysts. It is demonstrated that the ΔG_OH* value in the volcano plot is optimized by proper desodiation. Meanwhile, the lattice strain introduced along with the desodiated process modulates the ΔG_OH*, according to first principle calculations. It shows that ∼0.157 % compressive strain in the CoO₂ layers and ∼1% tensile strain between CoO₂ layers are introduced in the desodiated Ag doped Na_0.7CoO₂. Among these catalysts, the desodiated Ag-Na_0.7CoO₂ sample exhibits an optimal RuO₂-beyond water oxidation (OER) activity with the lowest overpotential of 236 mV@10 mA/cm², the smallest Tafel slope of 48 mV/dec and the highest mass current density of 227.8 A/g. This work provides an interesting avenues to optimize existing layered materials with inter/intralayer modifications for highly efficient water oxidation electrolysis.