Development of a Hydrogen Evolving Photocatalytic Membrane

Photoelectrochemical cells have a fundamental problem in that the thin, closely spaced laminar phases normally comprising an electrochemical cell do not readily lend themselves to penetration by external light as part of a solar energy conversion scheme. This has led to novel cell configurations that are more amenable to solar absorption. We are working on a “photocatalytic membrane”, where a single sheet comprised of two semiconductor layers combine their photopotentials to achieve a water-splitting voltage. A schematic depicting how the membrane might be configured is shown below. Light absorption in respective semiconductor layers drives oxidation on one side of the membrane and reduction on the other. Perforations filled with ion-exchange polymer allow the flow of ionic charge carriers (hydronium ion in acidic media) between anolyte and catholyte compartments. To fabricate such a photocatalytic membrane, a sequence of deposition steps must be developed where each subsequent step is compatible with the previous ones. Our strategy is to build n-type and p-type layers on opposite sides of a thin, perforated metallic sheet. A prototype device involving electrodeposition of n-WO3 and p-CdTe on mechanically perforated stainless #304 has been fabricated. A net photovoltage of 0.8 V in aqueous acidic electrolyte was estimated.