(217g) BiVO4/WO3 Photoanodes for Chloride Oxidation with Simultaneous H2 Production

The most actively pursued application of photoelectrocatalytic fuel production is the decomposition of water to make hydrogen and oxygen (a.k.a. solar water splitting). Although the physical phenomena are reasonably well understood, the hurdle with solar water splitting is the development of a commercially a cost-effective system that can produce H₂ fuel with an overall energy efficiency of at least 10% or higher for a sustained period of time. One reason water splitting is expensive, is one half of the reaction is the 4 electron oxidation of water which is kinetically sluggish and results in the production of O₂, which has limited economic value. Electrooxidation of chloride ions which are increasingly abundant could provide an attractive, cost-effective option to water oxidation.

The focus of the current work is to carry out chloride oxidation in acidic pH (pH 1) using nanoporous bismuth vanadate (BiVO₄) as the light absorber, and use electrons provided from the oxidation step to generate hydrogen at the dark cathode. BiVO₄ has been widely regarded as a promising low-cost photoanode for solar to chemical energy conversion. However, most of the demonstrated work with BiVO₄ so-far has been limited to neutral or slightly basic pH, where BiVO₄ has been shown to be chemically and photoelectrochemically stable. For chloride oxidation, the pH of the electrolyte should be less than 3 to obtain high chlorine production yield. To address the above challenge, we report on a method to electrodeposit tens of nanometer thick amorphous tungsten oxide (WO₃) films on top of nanoporous crystalline BiVO₄ electrodes, and benchmark its activity for Cl^- oxidation.