(Invited) Lignin for Power- and Solar-to-Chemical Energy Conversion: An Alternative Electron Source and Its Valorization

Abstract

Electrochemical and photoelectrochemical synthesis is a promising technology for the efficient use of clean but intermittent renewable energy resources. In principle, various chemicals can be produced in a sustainable manner through (photo)electrochemical reduction using water as a cheap and clean source of electrons. However, oxidation of water is a challenging task and acts as a bottleneck for the practical application of solar- and power-to-chemical energy conversion due to slow kinetics originating from its complex four-electron transfer process. In addition, it requires the use of expensive catalysts and causes reliability issues. In this presentation, we report that various types of biomass wastes can be used as cheap and efficient electron sources. In particular, electrons can be readily extracted from biomass using phosphomolybdic acid (PMA), which can act as a catalyst for oxidative depolymerization of biomass and an electron mediator. PMAs can be reduced upon oxidation of biomass and then oxidized on an anode at a potential much lower than that for water oxidation. Furthermore, value-added chemicals such as CO and vanillin are produced as byproducts upon oxidative depolymerization of lignin. As a result, this approach allows efficient (photo)electrochemical production of hydrogen at acidic pHs and brings additional economic benefits from byproducts.