Experimental and theoretical investigation of sulfur-doped g-C3N4 nanosheets/FeCo2O4 nanorods S-scheme heterojunction for photocatalytic H2 evolution

g-C₃N₄ emerges as a promising metal-free semiconductor photocatalyst due to its cost-effectiveness, facile synthesis, suitable visible light response, and robust thermal stability. However, its practical application in photocatalytic hydrogen evolution reaction (HER) is impeded by rapid carrier recombination and limited light absorption capacity. In this study, we successfully develop a novel g-C₃N₄-based step-scheme (S-scheme) heterojunction comprising two-dimensional (2D) sulfur-doped g-C₃N₄ nanosheets (SCN) and one-dimensional (1D) FeCo₂O₄ nanorods (FeCo₂O₄), demonstrating enhanced photocatalytic HER activity. The engineered SCN/FeCo₂O₄ S-scheme heterojunction features a well-defined 2D/1D heterogeneous interface facilitating directed interfacial electron transfer from FeCo₂O₄ to SCN, driven by the lower Fermi level of SCN compared to FeCo₂O₄. This establishment of electron-interacting 2D/1D S-scheme heterojunction not only facilitates the separation and migration of photogenerated carriers, but also enhances visible-light absorption and mitigates electron-hole pair recombination. Band structure analysis and density functional theory calculations corroborate that the carrier migration in the SCN/FeCo₂O₄ photocatalyst adheres to a typical S-scheme heterojunction mechanism, effectively retaining highly reactive photogenerated electrons. Consequently, the optimized SCN/FeCo₂O₄ heterojunction exhibits a substantially high hydrogen production rate of 6303.5 µmol·g⁻¹·h⁻¹ under visible light excitation, which is 2.4 times higher than that of the SCN. Furthermore, the conjecture of the S-scheme mechanism is confirmed by in situ XPS measurement. The 2D/1D S-scheme heterojunction established in this study provides valuable insights into the development of high-efficiency carbon-based catalysts for diverse energy conversion and storage applications.