Surface Reconstruction on Metal Nitride during Photo‐oxidation

Abstract The efficient conversion and storage of solar energy for chemical fuel production presents a challenge in sustainable energy technologies. Metal nitrides (MNs) possess unique structures that make them multi‐functional catalysts for water splitting. However, the thermodynamic instability of MNs often results in the formation of surface oxide layers and ambiguous reaction mechanisms. Herein, we present on the photo‐induced reconstruction of a Mo‐rich@Co‐rich bi‐layer on ternary cobalt‐molybdenum nitride (Co 3 Mo 3 N) surfaces, resulting in improved effectiveness for solar water splitting. During a photo‐oxidation process, the uniform initial surface oxide layer is reconstructed into an amorphous Co‐rich oxide surface layer and a subsurface Mo−N layer. The Co‐rich outer layer provides active sites for photocatalytic oxygen evolution reaction (POER), while the Mo‐rich sublayer promotes charge transfer and enhances the oxidation resistance of Co 3 Mo 3 N. Additionally, the surface reconstruction yields a shortened Co−Mo bond length, weakening the adsorption of hydrogen and resulting in improved performance for both photocatalytic hydrogen evolution reaction (PHER) and POER. This work provides insight into the surface structure‐to‐activity relationships of MNs in solar energy conversion, and is expected to have significant implications for the design of metal nitride‐based catalysts in sustainable energy technologies.