The effectiveness of reduced graphene oxide (RGO) in water reduction on a CuGaS2 photocathode was demonstrated. Graphene oxide was photocatalytically reduced over CuGaS2 particles under visible light irradiation to give an RGO–CuGaS2 composite. The incorporated RGO dramatically enhanced the cathodic photocurrent of the CuGaS2 photoelectrode under visible light irradiation. Detection of evolved H2 indicated that the enhanced cathodic photocurrent was used for water reduction to H2. Upon combining the developed RGO–CuGaS2 composite photocathode with a BiVO4 photoanode loaded with a CoOx cocatalyst, photocurrent and the corresponding H2 evolution were successfully observed without applying an external bias between both photoelectrodes under simulated sunlight irradiation.

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