Nano-sized quaternary CuGa₂In₃S₈ as an efficient photocatalyst for solar hydrogen production

The synthesis of quaternary metal sulfide (QMS) nanocrystals is challenging because of the difficulty to control their stoichiometry and phase structure. Herein, quaternary CuGa₂In₃S₈ photocatalysts with a primary particle size of ∼ nm are synthesized using a facile hot-injection method by fine-tuning the sulfur source injection temperature and aging time. Characterization of the samples reveals that quaternary CuGa₂In₃S₈ nanocrystals exhibit n-type semiconductor characteristics with a transition band gap of ∼1.8eV. Their flatband potential is located at -0.56 V versus the standard hydrogen electrode at pH 6.0 and is shifted cathodically by 0.75 V in solutions with pH values greater than 12.0. Under optimized conditions, the 1.0 wt% Ru-loaded CuGa₂In₃S₈ photocatalyst exhibits a photocatalytic H₂ evolution response up to 700 nm and an apparent quantum efficiency of (6.9±0.5)% at 560 nm. These results indicate clearly that QMS nanocrystals have great potential as nanophotocatalysts for solar H₂ production.