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.