IMPROVEMENT OF PHOTOELECTROCHEMICAL HYDROGEN GENERATION BY SURFACE MODIFICATION OF p-TYPE SILICON SEMICONDUCTOR PHOTOCATHODES.

The improvement of H//2 evolution from two different types of catalytic p-type photocathode surfaces has been examined. p-Type Si has been platinized by photoelectrochemically plating Pt(O) onto the Si surface. Such a photocathode shows significant improvement (compared to naked p-type Si) for photochemical H//2 evolution with respect to output photovoltage, fill factor, and overall efficiency. Such photocathodes having an optimum amount of Pt(O) give a pH-dependent output voltage with respect to the H//2O/H//2 couple, but the dependence is not a simple 59-mV/pH dependence. No pH dependence would be expected if Pt(O) formed a Schottky barrier when plated onto p-type Si. A second kind of H//2 evolution catalyst has been confined to the surface of p-type Si. Polymeric quantities of an electroactive N,N**'-dialkyl-4,4**'-bipyridinium reagent, (PQ**2** plus **/** plus **. )//n, have been confined to the surface. The Br** minus counterions of the polymer are then exchanged by PtCl//6**2** minus . Photoreduction then yields Pt(O) dispersed in the polymer. Such a surface is again significatnly improved compared to naked p-type Si with respect to H//2 evolution.