Light Inducing the Geometric Conversion of NiO₆ to Trigger a Faster Oxygen Evolution Reaction Pathway: The Coupled Oxygen Evolution Mechanism

Developing highly active and robust oxygen evolution reaction (OER) electrocatalysts is still a critical challenge for water electrolyzers and metal–air batteries. Realizing the dynamic evolution of the intermediate and charge transfer during OER and developing a clear OER mechanism is crucial to design high-performance OER catalysts. Recently in Nature, Xue and colleagues revealed a new OER mechanism, coupled oxygen evolution mechanism (COM), which involves a switchable metal and oxygen redox under light irradiation in nickel oxyhydroxide-based materials. This newly developed mechanism requires a reversible geometric conversion between octahedron (NiO₆) and square planar (NiO₄) to achieve electronic states with both “metal redox” and “oxygen redox” during OER. The asymmetric structure endows NR-NiOOH with a nonoverlapping region between the dz² orbitals and a_1g* bands, which facilitate the geometric conversion and enact the COM pathway. As a result, NR-NiOOH exhibited better OER activity and stability than the traditional NiOOH.