Design and application of g-C₃N₄-based materials for fuels photosynthesis from CO₂ or H₂O based on reaction pathway insights

Photocatalytic CO₂ reduction reaction (CRR) and hydrogen evolution reaction (HER) based on graphitic carbon nitride (g-C₃N₄) that is regarded as the metal-free "holy grail" photocatalyst, provide promising strategies for producing next-generation fuels, contributing to achieving carbon neutrality, alleviating energy and environment crisis. However, the activity of CRR and HER over g-C₃N₄ leaves much to be desired. Therefore, numerous studies have sprung up to enhance photoactivity. A comprehensive understanding of the CRR and HER reaction pathways is crucial for designing g-C₃N₄-based materials, further promoting efficient fuel production. Different from previous reviews that focus on g-C₃N₄ modification from the viewpoint of material science. In this review, we divided the multistep processes of CRR and HER into five reaction pathways and summarized the latest advances for improving each pathway of fuels synthesis through CRR or HER. Meanwhile, the existing bottleneck issues of each step were also discussed. Finally, comprehensive conclusions, including the remaining challenges, outlooks, etc., for CRR and HER over g-C₃N₄ were put forward. We are sure that this review will conduce to the understanding of the structure-activity relationship between CRR, HER processes, and g-C₃N₄ structure, which can provide the reference for developing high-powered photocatalysts, not confined to g-C₃N₄.