Rational construction of carbon nitride homojunction photocatalyst for enhanced hydrogen evolution from water splitting

Solar energy-driven photocatalytic H2 evolution is a clean and sustainable energy conversion technology, in which the hinge lies on developing an efficient photocatalyst. Homojunction is an effective manner to improve photocatalytic performance, however, its successful design and construction have always been a challenge. Herein, a facile approach of molten-salt assisted two-step thermal polymerization strategy is innovatively developed to prepare a unique polymer carbon nitride (PCN)-based homojunction photocatalyst (HLPCN), which not only creates different PCN regions with high and low crystallization but also the closely combined homo-interface. As a consequence, the as-prepared HLPCN homojunction exhibits Z-scheme mechanism, accelerating the separation of photocarriers and reserving photogenerated electrons with a strong reducibility. Plus the help of MoS2 cocatalyst, the optimized HLPCN shows a photocatalytic H2 evolution rate of 8193 µmol∙g−1·h−1, which is up to 27.2 and 17.2 times of the low crystalline PCN (LPCN) and high crystalline PCN (HPCN), respectively, and exceeds many well-designed PCN-based photocatalytic system using Pt as cocatalyst. Besides that, HLPCN also shows high H2 evolution from seawater splitting of 5694 µmol∙g−1·h−1 in the simulated seawater and 6318 µmol∙g−1·h−1 in the real seawater. This work showcases a novel method to design and construct PCN homojunction with great potential in the application of solar to energy photocatalysis.