Effect of Electrolytes on the Selectivity and Stability of n-type WO3 Photoelectrodes for Use in Solar Water Oxidation

High surface area porous n-type WO3 electrodes were prepared electrochemically and used as a photoanode in a water-splitting photoelectrochemical cell. Various electrolytes containing different anions (acetate, chloride, phosphate, perchlorate, and sulfate) and cations (Li+, Na+, and K+) were prepared at pH 1, 3, and 5 to investigate how these anions and cations affect the efficiency of the photo-oxidation reaction of water on the WO3 surface. To quantitatively compare their effects on O2 evolution, photocurrent to oxygen conversion efficiency was obtained for each electrolyte by simultaneously measuring photocurrent and O2 produced in a sealed divided cell. The type of competing reactions present in each electrolyte and their effects on water oxidation to O2 or to hydrogen peroxide, which is known to accumulate on the WO3 surface and cause photocorrosion, were investigated. The results reported in this study will be useful in formulating optimum electrolyte compositions to enhance desired photo-oxidation reactions for various photoelectrochemical cells.