Recent Progress on Photoelectrochemical Water Splitting of Graphitic Carbon Nitride (g-CN) Electrodes

Graphitic carbon nitride (g-CN), a promising visible-light-responsive semiconductor material, is regarded as a fascinating photocatalyst and heterogeneous catalyst for various reactions due to its non-toxicity, high thermal durability and chemical durability, and "earth-abundant" nature. However, practical applications of g-CN in photoelectrochemical (PEC) and photoelectronic devices are still in the early stages of development due to the difficulties in fabricating high-quality g-CN layers on substrates, wide band gaps, high charge-recombination rates, and low electronic conductivity. Various fabrication and modification strategies of g-CN-based films have been reported. This review summarizes the latest progress related to the growth and modification of high-quality g-CN-based films. Furthermore, (1) the classification of synthetic pathways for the preparation of g-CN films, (2) functionalization of g-CN films at an atomic level (elemental doping) and molecular level (copolymerization), (3) modification of g-CN films with a co-catalyst, and (4) composite films fabricating, will be discussed in detail. Last but not least, this review will conclude with a summary and some invigorating viewpoints on the key challenges and future developments.