Photocatalytic hydrogen production via g-C3N4 based S-scheme heterojunctions: Mechanism and design principles

The need for new and cost-effective ways to produce hydrogen from solar light is important in developing solutions to our current energy needs. Graphitic carbon nitride (g-C 3 N 4 ) is a promising photocatalyst because it is a chemically inert that absorbs visible light; however, the practical application of g-C 3 N 4 has been hindered by several drawbacks including rapid recombination of electrons and holes upon excitation, low redox potential, and limited solar light absorption. Recent advancements have included the use of S-scheme heterostructure design to improve spatial separation of electron-hole pairs and increase visible light absorption while maintaining the strong redox capabilities needed for efficient hydrogen gas production. Therefore, this review explores the design of g-C 3 N 4 based S-scheme heterojunctions with enhanced photocatalytic hydrogen evolution activity and describe the key concepts associated with the S-scheme electron-hole transfer process, material combinations, interface modifications, and mechanistic understanding provided by advanced characterization methods. Finally, the review summarizes the current challenges and provide recommendations for future work intended to improve the scalability and efficiency of g-C 3 N 4 based S-scheme heterojunctions for hydrogen production.