The efficiency of photogeneration of hydrogen at p-type III/V semiconductors

• Published in: Journal of electroanalytical chemistry and interfacial electrochemistry 1981-02, Vol.119 (1), p.109-123
• Main Authors: Dare-Edwards, M.P., Hamnett, A., Goodenough, J.B.
• Format: Article
• Language: English
• ISSN: 0022-0728
• DOI: 10.1016/S0022-0728(81)80127-1

Studies have been carried out on p-GaP and other III/V p-type semiconductors in an attempt to understand the reasons for the very low efficiency of photogeneration of hydrogen at potentials just positive of flatband. The efficiency for this process only rises to significant levels at potentials >0.6 V from flatband, which prevents the effective use of these photoelectrodes in solar photoelectrolysis cells. The poor response has been found to be caused by surface hydrogen atoms formed in the first step of the photo-assisted hydrogen evolution reaction. In addition to their subsequent conversion to H 2, these atoms may be reoxidised by holes tunnelling to the surface from the valence band; this process is only suppressed at very negative potentials. Evidence for this model is provided by ac and dc experiments and a detailed impedance analysis. It has been found that the response of p-GaP may be improved dramatically by the adsorption of a layer of Ru(III) chloride. This also appears to effect a reduction in the tunnelling reaction.