Synergistic promotion of charge dynamics, H₂O activation, and dehydrogenation for enhanced visible-light H₂ production on modified TiO₂

To simultaneously improve the critical factors in photocatalytic H₂ production, the population of active photogenerated electrons, the adsorption and activation of H₂O molecules, and the surface dehydrogenation efficiency, we propose a synergistic strategy for TiO₂ modification by combining transition metal (TM) doping and N-doped carbon (N-C) coating. The targeted Cr-TiO₂@N-C heterojunction exhibits dramatically enhanced H₂ production under blue light irradiation, contrasting sharply with a negligible production by pristine TiO₂. Comprehensive structural characterization and theoretical calculations confirm the uniform substitution of Cr into the TiO₂ lattice, promoting the formation of adjacent oxygen vacancies (V_O). The synergistic effect of Cr doping and V_O extends the light absorption range into the visible region. The coated N-C layer facilitates the efficient separation of photogenerated charge carriers, boosting the population of active electrons. Critically, the combined action of V_O and N-C layer enhances the adsorption and activation of H₂O molecules while effectively improving the subsequent surface dehydrogenation efficiency. Significantly, this strategy demonstrates broad universality: Analogous TM-TiO₂@N-C heterojunctions (TM = Mn, Co, Ni, Cu, and Zn) synthesized via the same approach all show substantially improved H₂ production performance over pristine TiO₂.