Hydrogen Evolution at p ‐ InP Photocathodes in Alkaline Electrolyte

Abstract

The photoelectrochemical (PEC) performance of p-TnP single crystal, surface modified by the sequentialdeposition of cobalt and platinum, has been investigated in 6N KOH. Efficiencies of 14.2% were realized from the photocathode for the electrical power savings obtained compared to a platinum cathode, operating at the same current density. A variety of definitions of efficiency for the conversion of light to hydrogen are discussed. RESULTS AND DISCUSSIONSeveral approaches have been discussed previously for improving the performance of photoelectrodes by surface modification procedures. These have been discussed in several PEC review articles (1-4). The role of platinum for improving the performance of ironoxide photoanodes was discussed by us some time ago to assist the photoelectrochemical oxygen-evolution reaction (15). Improving the performance of p~InP in both acid (6,7,8) and alkaline electrolyte (9) for specific photoelectrochemical reactions has also been observed. We wish to report on the enhanced performance of p-lnP photocathodes realized by the sequential deposition of Co and Pt on its surface.The p-lnP single crystals (Zn-doped, carrier density 1016/cm 3, <IIi> surface, obtained from Crysta Comm Inc.) were used in the course of this work. Ohmic contact to the crystal was made by the sequential deposition of Au-Zn-Au followed by sintering at 475oc for 20 seconds. Current collection was via a nickel wire to the ohmic contact using silver epoxy which was then cured at 150~ for one hour. After encapsulation of this current collector and the semiconductor edges, the photocathode surface was etched with concentrated HCI for I0 seconds, during which time gas evolution was observed. Surface modification of *Electrochemical Society Active Member.

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