Phosphomolybdic Acid as a Catalyst for Oxidative Valorization of Biomass and Its Application as an Alternative Electron Source

Power- and solar-to-chemical energy conversion has been spotlighted as a promising technology for the efficient use of renewable energy resources. In principle, various chemicals can be sustainably produced through (photo)electrochemical reduction using water as a cheap and clean electron source. However, oxidation of water is a challenging task that results in low energy efficiency and reliability issues for the practical application of power- and solar-to-chemical energy conversion. Here, we show that various biomasses including lignin can be used as alternative electron sources. Electrons can be readily extracted from biomass using phosphomolybdic acid as a catalyst for oxidative depolymerization of biomass and an electron mediator at a much lower potential (0.95 V vs reversible hydrogen electrode) than water using best-performing but expensive catalysts (1.5-1.6 V). In particular, value-added chemicals such as CO and vanillin are produced as by-products upon oxidative depolymerization of lignin. As a result, this approach allows efficient (photo)electrochemical production of hydrogen with a Faradaic efficiency close to unity at acidic pHs and brings additional economic benefits from by-products.