Three-Dimensional Ordered Macroporous TiO2–TaOxNy Heterostructure for Photoelectrochemical Water Splitting

Three-dimensional (3D) ordered macroporous (such as inverse opal) heterostructure materials are attractive for photocatalysis because of their interconnected pores, high surface area, light-harvesting properties, and favorable charge-transfer properties. In this work, we report the preparation of TiO2–TaOxNy heterostructure inverse opals using atomic layer deposition and investigate their photoelectrochemical performance. Through ultraviolet photoelectron spectroscopy analyses of the band alignment of TiO2 and TaOxNy, we confirm that a type II heterojunction is formed. The deposition temperature of TaOxNy is found to play an important role in achieving homogeneous infiltration, leading to a uniform TiO2/TaOxNy heterostructure. The TiO2–TaOxNy photoanode achieved a twofold increase in photocurrent density, a lower onset potential, and improved stability in an alkaline electrolyte; overcoming the drawbacks of standalone TiO2 and TaOxNy. These improvements can be attributed to the appropriate type II band alignment, which generates a large built-in electric field, thus promoting charge carrier separation, reducing the accumulation of photogenerated carriers at the semiconductor/electrolyte interface, and improving minority carrier transport.