PHOTOELECTROCHEMICAL DISSOCIATION OF WATER AT COPPER-DOPED P-GAAS ELECTRODES

Cu-doped p-GaAs was used as a photocathode in a three-electrode electr ochemical cell. It was illuminated with visible light in 0.05M H2SO4. The onset potential of photocurrent and H2O decomposition was about 0. 6 V, cathodic with respect to the flat-band potential of p-GaAs (0.3 V vs SCE). The photocurrent anomaly near the flat-band potential (V(fb) ) was attributed to the poor catalytic properties of p-GaAs towards H- 2 evolution. It was also attributed to the existence of a surface stat e which can trap the photoexcited electrons from the conduction band. The deposition of five monolayers of Pt over the GaAs surface shifted the onset potential of photocurrent by 0.1 V towards the positive dire ction. Upon illumination of p-GaAs, H-2 evolved over it and O2 evolved over the Pt counter-electrode in a 2:1 ratio. Their evolution obeys z ero-order kinetics. The photocurrent as well as the water decompositio n changed linearly with light intensity.