Light-triggered oxygen redox activity at the edge of cobalt oxyhydroxide for superior water oxidation.

Introducing oxygen redox chemistry into cobalt oxyhydroxide effectively enhances catalytic activity by enabling direct O-O coupling, thereby bypassing the rate-limiting *OOH step in the conventional adsorbate evolution mechanism. However, the key challenge is to preserve the accessibility of non-bonding oxygen states while maintaining cobalt-oxygen covalency. Here we show that light irradiation triggers ligand-to-metal charge transfer in sulfur-treated cobalt oxyhydroxide (S-CoOOH), generating non-bonding oxygen states. These states then couple with adjacent ones to form direct O-O bonds. Through this way, the sulfur-treated sample performs enhanced OER activity under light, achieving an overpotential of 194 ± 3 mV at 10 mA cm-2, which is 41 mV lower than in the dark. Further analysis reveals that light-induced oxygen redox activity is confined to the edge of catalyst. This activity originates from electron transitions from (M-O) to non-overlapping regions of Co 3 d and 4p orbitals, driven by high-spin Co3+ at the edge. This work highlights the critical role of light in inducing non-bonding oxygen states in transition metal-based catalysts and guides the development of oxygen-redox electrocatalysts.