Optimization of oxygen evolution activity by tuning e *g band broadening in nickel oxyhydroxide

Abstract

Nickel oxyhydroxides (NiOOH) derived from the reconstruction of Ni-based pre-catalysts are active species for the oxygen evolution reaction (OER). Although chemically similar, these NiOOH exhibit differentiated OER activities that show strong correlations to their synthetic origins. To unearth the mechanism behind this, three NiOOH were prepared by subjecting NiS₂, NiSe₂ and Ni₅P₄ to chronopotentiometry treatment. We found that a stronger strain leads to a greater NiO₆ octahedron distortion in NiOOH, which results in the broadening of the band (3d electron states with e_g symmetry) to a great extent. The increase in band broadening can facilitate electron transfer from the electrocatalysts to the external circuit, which ultimately enhances the catalytic performance. We demonstrated the universality of this concept by extending it to a NiFe oxyhydroxide system. This study shows the first evidence of the relationship between structure and catalytic performance by revealing the role of band broadening, paving the way toward designing efficient OER electrocatalysts.