Design of polymeric carbon nitride-based heterojunctions for photocatalytic water splitting: a review

Developing high-efficiency and stable photocatalysts able to accomplish spontaneous overall water splitting, without using sacrificial agents, is the ultimate goal of photocatalytic solar–hydrogen production. Metal-free polymeric carbon nitride (CN) has emerged as a promising alternative for photocatalytic water splitting, owing to its excellent physicochemical properties. In the past decade, various strategies, including thermodynamic and kinetic modifications, have been employed to improve the photocatalytic activity of CN. Among these modification strategies, constructing heterojunctions has stimulated intensive research interest due to the enhanced efficiency of carrier separation, and hence the photocatalytic performance. This article reviews the recent progress of CN-based heterojunction photocatalysts for overall water splitting, highlighting the characteristics and fundamental design principles of different heterojunctions from the viewpoint of interfacial charge properties and energy band offsets. Finally, perspectives on the challenges and opportunities for developing advanced CN-based heterojunction photocatalysts are provided.