Three-dimensional ordered macroporous TiO₂−Tao_xn_y 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− TaO_xN_y heterostructure inverse opals using atomic layer deposition and investigate their photoelectrochemical performance. Through ultraviolet photoelectron spectroscopy analyses of the band alignment of TiO₂ and TaO_xN_y, we confirm that a type II heterojunction is formed. The deposition temperature of TaO_xN_y is found to play an important role in achieving homogeneous infiltration, leading to a uniform TiO₂/TaO_xN_y heterostructure. The TiO₂−TaO_xN_y 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 TaO_xN_y. 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.