Potassium-doped g-C3N4/nitrogen-doped g-C3N4 step-scheme homojunction for enhanced H2 evolution photocatalysis

Developing a promising step-scheme (S-scheme) heterojunction is an effective strategy to achieve high photocatalytic activity for hydrogen evolution reaction (HER). However, the difference in microstructure and energy level matching between two semiconductors confers limited catalytic activity of traditional S-scheme heterojunctions. In this work, a strong interfacial coupled S-scheme homojunction composed of potassium-doped g-C3N4 and nitrogen-doped g-C3N4 (K-CN/N-CN) is constructed successfully as an efficient HER catalyst. The engineered K-CN/N-CN not only features well-defined two-dimensional (2D) lamellar morphology with strong interfacial electron interactions but also possesses efficient light utilization and favorable carrier migration dynamics. Subsequent density functional theory (DFT) calculations confirm the optimal hydrogen adsorption Gibbs free energy (Delta G(H*)) for K-CN/N-CN homojunction, which is extremely close to zero (-0.06 eV). Importantly, the migration of photogenerated electron-hole pairs for the K-CN/N-CN adheres to a typical S-scheme carrier transfer mechanism, which effectively retains the strongly reducing photoexcited electrons. Consequently, the optimal K-CN/N-CN S-scheme homojunction displays a high H-2 evolution rate of 8.7 mmol g(-1) h(-1) under visible light excitation, which is similar to 72 times higher than that of the CN. The S-scheme homojunction developed in this study provides valuable insights for further strategic design and construction of high-performance catalysts.