Ultrathin Cobalt–Manganese Nanosheets: An Efficient Platform for Enhanced Photoelectrochemical Water Oxidation with Electron‐Donating Effect

Abstract An ultrathin cobalt–manganese (Co‐Mn) nanosheet, consisting of amorphous Co(OH) x layers and ultrasmall Mn 3 O 4 nanocrystals, is designed as an efficient co‐catalyst on an α‐Fe 2 O 3 film for photoelectrochemical (PEC) water oxidation. The uniformly distributed Co‐Mn nanosheets lead to a remarkable 2.6‐fold enhancement on the photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) and an impressive cathodic shift (≈200 mV) of onset potential compared with bare α‐Fe 2 O 3 film. Furthermore, the decorated photoanode exhibits a prominent resistance against photocorrosion with excellent stability for over 10 h. Detailed mechanism investigation manifests that incorporation of Mn sites in the nanosheets could create electron donation to Co sites and facilitate the activation of the OH group, which drastically increases the catalytic activities for water oxidation. These findings provide valuable guidance for designing high‐performance co‐catalysts for PEC applications and open new avenues toward controlled fabrication of mixed metallic composites.