Electrocatalytic valorization of lignin

Abstract

Lignin is the largest resource of biobased renewable aromatic feedstock for chemicals and fuels. For profitable biorefineries, lignin valorization is essential, as it enhances the overall efficiency of biomass conversion and improves process economics. In recent decades, lignin valorization and depolymerization processes have attracted significant scientific interest. Many approaches have been explored, including thermochemical methods, such as pyrolysis, oxidative depolymerization, and reductive catalytic fractionation; biological methods, like enzymatic depolymerization and microbial degradation; and electrochemical techniques, such as electrocatalytic oxidation and electrocatalytic hydrogenation. Among them, electrochemical processes play a significant role in lignin valorization by employing green electricity sources with in situ hydrogen generation, being environmentally friendly, and contributing to the economic feasibility of lignin conversion. In this review, the electrochemical conversion of lignin from lignocellulosic biomass, including lignin fractionation or depolymerization to lignin derived compounds (such as vanillin, benzoic acid and quinones) through electrocatalytic oxidation, and its upgrading through electrocatalytic hydrogenation or hydrogenolysis to produce industrially valuable lignin-based chemicals, are discussed in detail. Finally, a summary of current challenges, limitations and emerging opportunities in electrochemical valorization of lignin is provided to frame this technology for sustainable and biobased development.