Electrochemical Biorefinery toward Chemicals Synthesis and Bio-Oil Upgrading from Lignin

Recalcitrance and the inherent heterogeneity of lignin structure are the major bottlenecks to impede the popularization of lignin-based chemicals production processes. Recent works suggested a promising pathway for lignin depolymerization and lignin-derived bio-oil upgrading via an electrochemical biorefinery (a process in which lignin valorization is performed via electrochemical oxidation or reduction). This review presents the progress on chemicals synthesis and bio-oil upgrading from lignin by an electrochemical biorefinery, relating to the lignin biosynthesis pathway, reaction pathway of lignin electrochemical conversion, inner-sphere and outer-sphere electron transfer mechanism, basic kinetics and thermodynamics in electrochemistry, and the recent embodiments analysis with the emphasis on the respective feature and limitation for lignin electrochemical oxidative and reductive conversion. Lastly, the challenge and perspective associated with lignin electrochemical biorefinery are discussed. Present-day results indicate that more work should be performed to promote efficiency, selectivity, and stability in pursuing a lignin electrochemical biorefinery. One of the most promising developing directions appears to be integrating various types of lignin electrochemical conversion strategies and other existing or evolving lignin valorization technologies. This review aims to provide more references and discussion on the development for lignin electrochemical biorefinery.