Direct Sulfurization of Liquid Gallium for Scalable GaS/Ga ₂ S ₃ Heterophotocatalysts for Hydrogen Evolution

High Resolution Image Download MS PowerPoint Slide We report a low-temperature chemical vapor deposition approach that enables the direct formation of GaS at 300 °C and controlled transformation to Ga 2 S 3 by tuning the sulfurization temperature and time. Comprehensive structural analyses reveal that pure GaS forms below 450 °C, while mixed GaS/Ga 2 S 3 heterostructures emerge above 500 °C and evolve to phase-pure α′-Ga 2 S 3 after prolonged annealing at 700 °C. X-ray photoelectron spectroscopy (XPS) confirms a time-dependent decrease in the GaS:Ga 2 S 3 ratio from 1:1.56 to complete Ga 2 S 3 conversion, accompanied by binding energy shifts that evidence interfacial electron transfer from GaS to Ga 2 S 3 . Transmission electron microscopy further resolves atomically sharp GaS/Ga 2 S 3 interfaces with coherent lattice matching. Electrochemical impedance spectroscopy demonstrates that M-Ga 2 S 3 /GaS heterostructures, containing an intermediate Ga 2 S 3 fraction, exhibit the lowest charge-transfer resistance (∼37 kΩ) and the highest steady-state photocurrent (∼400 nA). The heterostructures deliver an exceptional hydrogen evolution rate of 2.93 mmol g –1 h –1, a 3.3-fold increase over that of pure Ga 2 S 3 . This outstanding activity is attributed to a type-II band alignment that drives electrons from GaS to Ga 2 S 3 and holes in the opposite direction, enhancing charge separation and suppressing recombination. Our results highlight a scalable low-temperature route to gallium sulfide heterostructures with precisely tunable phase composition and superior photocatalytic hydrogen production performance.