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

We report a low-temperature chemical vapor deposition approach that enables the direct formation of GaS at 300 °C and controlled transformation to Ga2S3 by tuning the sulfurization temperature and time. Comprehensive structural analyses reveal that pure GaS forms below 450 °C, while mixed GaS/Ga2S3 heterostructures emerge above 500 °C and evolve to phase-pure α′-Ga2S3 after prolonged annealing at 700 °C. X-ray photoelectron spectroscopy (XPS) confirms a time-dependent decrease in the GaS:Ga2S3 ratio from 1:1.56 to complete Ga2S3 conversion, accompanied by binding energy shifts that evidence interfacial electron transfer from GaS to Ga2S3. Transmission electron microscopy further resolves atomically sharp GaS/Ga2S3 interfaces with coherent lattice matching. Electrochemical impedance spectroscopy demonstrates that M-Ga2S3/GaS heterostructures, containing an intermediate Ga2S3 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 Ga2S3. This outstanding activity is attributed to a type-II band alignment that drives electrons from GaS to Ga2S3 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.