The effect of the Ga content on the photocatalytic hydrogen evolution of CuIn1−xGaxS2 nanocrystals

Abstract

We report on the photocatalytic hydrogen evolution under full-arc light irradiation of CuIn_1−xGa_xS₂ wurtzite nanocrystals in the presence of SO₃²⁻ and S²⁻ as sacrificial reagents. We analyzed the hydrogen generation rate as a function of the Ga content and associated it with the energy band positions. For photocatalytic water splitting, the CuInS₂ bandgap is slightly too low to efficiently overcome the reaction over-potential. The presence of Ga shifts up the CuInS₂ conduction band edge providing a larger driving force for photogenerated carriers to activate the water splitting reduction reaction. The larger the Ga content, the more energetically favorable the electron injection, and thus a more efficient use of the photogenerated carriers is reached. However, the band gap increase associated with the Ga incorporation reduces the concentration of photogenerated carriers available for water splitting, and consequently a lower hydrogen conversion rate is obtained for very high Ga contents. The optimum Ga concentration was experimentally found at CuIn_0.3Ga_0.7S₂.