(Invited) Photoelectrochemical Glycerol Oxidation to Value-Added Commodity Chemicals Using BiVO4-Based Photoanodes

Abstract

To create a functional photoelectrochemical cell (PEC) for solar fuels production, a cathode and anode reaction must both be chosen and optimized. In order to generate clean energy, a renewable resource such as water, nitrogen, or biomass, is typically reduced at the photocathode to generate H2, ammonia, or carbon-based fuel. In aqueous media, the anode reaction is typically water oxidation, as water is renewable and available in the cell. However, the product of water oxidation, O2, is not very valuable. As such, in recent years attention has been directed to finding a more attractive oxidation reaction that forms a value-added product that can be paired with reduction reactions of interest. Ideally, this reaction would consist of renewable, abundant, and affordable feedstock, such as biomass, that can be readily oxidized to a more valuable compound. The photoelectrochemical oxidation of glycerol to value-added commodity chemicals fits these criteria. Glycerol is the main byproduct of biodiesel production, and as such is cheap and abundant. As investment in clean fuels increases, the production of biodiesel will continue to increase, leading to an overabundance of glycerol, which can create storage and environmental issues. Developing systems to valorize glycerol will ensure sustainable biodiesel production and advance the transition to renewable fuels. Glycerol consists of three alcohol groups, and many oxidation pathways are possible, with the most profitable being the selective oxidation of the secondary alcohol to a ketone to make dihydroxyacetone (DHA). This conversion yields an over 200-fold value increase from $0.66 to $150 per kilogram. Thus, photoelectrochemical DHA production can provide an opportunity to make PEC operation more profitable while improving the sustainability of the biodiesel industry. BiVO4 is a good candidate for photoelectrochemical glycerol oxidation as it has a favorable band gap (2.4eV), excellent charge separation, and low water oxidation selectivity. In this presentation, we report our recent results obtained for photoelectrochemical glycerol oxidation using a BiVO4 photoanode. We will discuss various surface modifications of BiVO4 that we employed to elucidate the reaction mechanisms and to maximize the efficiency and selectivity for DHA production.