Photoreduction of Water by using Modified CuInS 2 Electrodes

Polycrystalline CuInS 2 films were fabricated by sulfurization of electrodeposited Cu and In metallic precursor films. Structural analyses revealed that the CuInS 2 film formed compact agglomerates of crystallites with grain sizes of ca. 0.5–1.5 μm. Photoelectrochemical characterization revealed that the film was p ‐type with a flat band potential of 0.3–0.4 V (vs Ag/AgCl at pH 4), which is suitable for water reduction but cannot be for water oxidation. Upon loading Pt deposits, the film worked as a hydrogen (H 2 ) liberation electrode under cathodic polarization. Moreover, by introduction of n‐type thin layers such as CdS and ZnS on the CuInS 2 surface before the Pt loading, appreciable improvements of H 2 liberation efficiency were achieved: for the CdS modified sample, spectral response data showed incident photon to current efficiency as high as 20 % at wavelengths ranging from ca. 500 to 750 nm. Appreciable H 2 evolution on this sample under potentials of power‐producing regions was also confirmed.