Interface Engineering between Photocatalyst and Cocatalyst: A Strategy for Enhancing Interfacial Charge Transfer and Water Oxidation of Layered Oxyhalides

Loading cocatalysts on photocatalysts is essential to enhance photocatalytic activity; however, the charge transfer from the photocatalyst to cocatalyst often governs the overall efficiency of the reactions. Nevertheless, their interface remains elusive and poses challenges for proactive control. The current study addresses the interface engineering to improve the O₂ evolution activity of oxyhalide photocatalysts by leveraging the unique band structures. Utilizing an oxyhalide Bi₄NbO₈Cl as a model photocatalyst, in which DFT calculations showed electrons and holes tend to accumulate in the fluorite and perovskite layer, respectively, we combined the exposure of the perovskite layer via acid treatment with the loading of water oxidation cocatalyst Ir species (hereafter denoted as IrO₂). This approach resulted in a 17-fold enhancement in the rate of evolution of the O₂ compared to unmodified pristine Bi₄NbO₈Cl. The observed O₂ evolution rate was markedly higher than that of the reported oxyhalide photocatalysts, with an apparent quantum efficiency reaching 16%. Various characterizations, including transient absorption spectroscopy, demonstrated that the significantly enhanced O₂ evolution was due to the efficient hole transfer between Bi₄NbO₈Cl and IrO₂, resulting from loading IrO₂ onto the perovskite layer (the hole accumulation layer) exposed through the acid treatment. By employing the surface-modified Bi₄NbO₈Cl as an O₂ evolution photocatalyst, we have achieved interparticle Z-scheme water splitting without any electron mediators. This research paves the way for rational control of photocatalyst-cocatalyst interface structures to improve the photocatalytic activities of various materials.