Organic Surface Passivation on Rh@CeO₂ Cocatalysts for Photocatalytic Overall Water Splitting

Decorating Rh cocatalysts with Cr₂O₃ overlayers can enhance the performance of photocatalytic overall water splitting (POWS). However, there is a general concern on the dissolution of Cr₂O₃, calling for the development of environment-friendly metal oxides. Here, we employ phenylphosphonic acid (PPOA) as a model surface modifier to decorate the model Rh@CeO₂ cocatalysts and demonstrate the critical role of organic surface passivation in H₂ evolution catalysis. We identify a "surface passivation effect" in photocatalysis, wherein the PPOA modification on CeO₂ overlayers not only suppress the adsorption and activation of oxygen but exhibit strong resistance to hydrogen reduction during POWS. This dual functionality effectively suppresses the reverse reactions by blocking the redox cycle of exposed Rh sites and defective CeO₂ overlayers, resulting in significantly enhanced photocatalytic activity and stability. Importantly, this strategy is not limited to Rh@CeO₂-PPOA systems; it also improves POWS performance in systems where other reducible oxides-organophosphonic acids structure are used as passivation layers on other noble metal cocatalysts. These findings provide fundamental insights into the universal principles of surface passivation in photocatalysis and offer a practical framework for regulating the reverse reactions and provide guidance for optimizing POWS through targeted surface organic modification.