Electrochemical valorization of lignin: Status, challenges, and prospects

As the second most abundant component of lignocellulosic biomass and the largest source of renewable aromatic compounds, lignin shows great potential to replace finite, non-renewable fossil oils and becomes a renewable feedstock for the production of fuel and aromatic chemicals. Therefore, it is highly important to develop efficient methods to convert lignin into biofuels and valuable chemicals. Electrochemical approaches are considered to be scalable, oxidant/reductant free, easy to control, and can be conducted under mild conditions. This review firstly overviews the structure and deconstruction methods of lignin. And then, different electrochemical lignin conversion approaches, including mediated electrooxidation, electroenzymatic oxidation, photoelectrochemical oxidation, and direct electrooxidation, are discussed in detail. The application of lignin-derived monomeric compounds is also briefly introduced. Finally, the advantages and challenges of different electrochemical lignin upgrading approaches are summarized; meanwhile, suggestions are made for future research on lignin biomass valorization.