An Efficient Mo-Doped Fe3S4 Co-Catalyst on TiO2 for Enhanced Photocatalytic Hydrogen Production

The development of earth-abundant co-catalysts that enhance TiO2-driven hydrogen evolution remains crucial for sustainable photocatalytic H2 production. This work investigates Mo addition as a compositional strategy to tune the co-catalytic functionality of Fe3S4 for photocatalytic HER over TiO2. A series of x%Mo–Fe3S4 (x = 0, 1, 2, 5, and 7.5) materials was prepared and evaluated using both conventional solvothermal synthesis (18 h) and a microwave-assisted non-aqueous sol–gel route requiring 30 min. When combined with anatase TiO2 as a model photocatalyst at a fixed co-catalyst loading (5 wt %), Mo addition markedly improved the performance of the Fe3S4 co-catalyst. Structural, surface, and optical characterizations indicate that Mo addition modifies the sulfides, in parallel with the observed improvement in co-catalytic hydrogen evolution reaction (HER) performance. Under UV–Vis irradiation (300 W Xe lamp), the best solvothermal composite (5%Mo-Fe3S4@TiO2) reached ∼30 μmol H2 h–1 after 3 h irradiation, corresponding to 25 times the rate of bare TiO2. For the microwave-derived series, the 7.5%Mo-Fe3S4@TiO2 composite delivered ∼29 μmol H2 h–1 after 3 h, corresponding to 24 times higher than bare TiO2, and 5 times higher than undoped Fe3S4@TiO2. Overall, Mo-doped Fe3S4 emerges as an earth-abundant, non-noble metal co-catalyst platform that significantly improves photocatalytic HER with TiO2 while maintaining performance under a time-efficient synthesis protocol.