Key role of e band broadening in nickel-based oxyhydroxides on coupled oxygen evolution mechanism.

A coupled oxygen evolution mechanism (COM) during oxygen evolution reaction (OER) has been reported in nickel oxyhydroxides (NiOOH)-based materials by realizing e band (3d electron states with e symmetry) broadening and light irradiation. However, the link between the e band broadening extent and COM-based OER activities remains unclear. Here, NiFeOOH (x = 0, 0.05, 0,2) are prepared to investigate the underlying mechanism governing COM-based activities. It is revealed that in low potential region, realizing stronger e band broadening could facilitate the OH deprotonation. Meanwhile, in high potential region where the photon utilization is the rate-determining step, a stronger e band broadening would widen the non-overlapping region between d and a orbitals, thereby enhancing photon utilization efficiency. Consequently, a stronger e band broadening could effectuate more efficient OER activities. Moreover, we demonstrate the universality of this concept by extending it to reconstruction-derived X-NiOOH (X = NiS, NiSe, NiP) with varying extent of e band broadening. Such an understanding of the COM would provide valuable guidance for the future development of highly efficient OER electrocatalysts.