Photocatalytic overall water splitting (OWS) without using any sacrificial reagent to realize H2 and O2 production in the stoichiometric ratio of 2:1 is viewed as the “holy grail” in the field of solar fuel production. Developing stable, low cost, and nontoxic photocatalysts that have satisfactory solar‐to‐hydrogen conversion efficiency is of significance but challenging for realizing the large‐scale use of this sustainable technology. Among various photocatalysts, graphitic carbon nitride (GCN) has shown great potential as an ideal candidate to fulfill the breakthrough in this dynamic research field due to its attractive physicochemical properties. Herein, for the first time, the state‐of‐the‐art research progress of GCN for photocatalytic OWS is reviewed. We first summarize the basic principle of photocatalytic OWS along with the advantages/challenges of GCN introduced. The strategies that have been used to modulate the OWS activity of GCN are then reviewed, including cocatalyst investigation, morphology modulation, atomic structure modification, crystallinity engineering, and heterostructure construction. Toward the end of the review, the concluding remarks and perspectives for the future development are presented, with our expectation to provide some new ideas for the design of advanced OWS photocatalysts.

Graphitic carbon nitride (g‐C3N4) is viewed as a promising visible‐light photocatalyst for industrialization due to its low processing temperature and high chemical stability. However, serious charge recombination caused by incomplete polymerization during direct calcination of nitrogen‐rich precursors significantly limits its photocatalytic performances. To boost charge separation, herein, we propose a rational strategy by constructing a crystalline g‐C3N4/g‐C3N4−xSx isotype heterostructure through the molten salt method. Theoretical calculation reveals that apparent charge‐transfer channels are formed between g‐C3N4 and S‐doped g‐C3N4 layers in the heterostructure. Owing to high crystallinity for decreasing charge recombination and isotype heterostructure for efficient charge transfer, the as‐prepared g‐C3N4/g‐C3N4−xSx showed remarkable photocatalytic performances with the hydrogen production rate elevated by up to 12.3 times of its singular components. Another novelty of this work is we investigated for the first time the piezocatalytic activity of crystalline g‐C3N4 by characterizing its performance for H2O2 generation and KMnO4 reduction. Strikingly, its superior piezocatalytic performance over components can be further improved by NaBH4 treatment, which is uncovered to enhance the asymmetric structure of crystalline g‐C3N4 by introducing extra cyano groups and removing partial NHx species in its tri‐s‐triazine layer structure. This work opens up new strategies for the design of highly efficient polymeric photocatalysts and highlights the piezocatalytic studies of g‐C3N4.

Graphitic carbon nitride is viewed as promising visible‐light photocatalyst. However, the high recombination rate of photogenerated carriers within the bulk strongly limits its performance and achieving highly efficient heterostructure remains challenging. Herein, construction of carbon nitride‐related heterostructures based on the one‐photon excitation pathway (OPEP) mechanism is reported and the complex interplay between component crystallinity and charge transfer kinetics is unraveled. As a proof of concept, prototype TiO2 is selected as the electron‐acceptor while crystalline carbon nitride (CCN) is used as the light‐absorber. Interestingly, a counter‐intuitive phenomenon is found that decreased crystallinity of the electron acceptor is favorable for charge carrier transfer through the heterostructure interface. Detailed structural analysis demonstrates TiO2 with low crystallinity can introduce more dramatic changes to electron distribution of C3N4 than those from highly crystalline counterparts when forming heterostructures, leading to the highly efficient interface. Based on the aforementioned observation, the designed heterostructure (CCN/low‐crystalline TiO2) presents a 6 and 4.8 times optimized photocatalytic hydrogen production rate of CCN and CCN/high‐crystalline TiO2, respectively. This finding challenges the conventional view and may advance the in‐depth understanding for construction of OPEP‐related heterostructures and design of highly efficient composite photocatalysts via structure modulation.

Piezoelectric assisted photocatalysis has emerged as an effective way to achieve higher utilization of charge carriers through the introduction of internal electric field. Even though in its infancy, the piezoelectric...

As the high-crystalline phase of carbon nitride, the poly(heptazine imide) (PHI) has attracted much attention in recent years considering its more effective light absorption, better charge carrier behaviors and higher...