Recent progresses on electro-oxidative lignin depolymerization for production of value-added chemicals

Abstract

Lignin represents the most abundant non-fossil aromatic carbon resource on Earth, and its efficient valorization is crucial for the full utilization of biomass and sustainable development. However, its complex three-dimensional structure and robust linkages pose significant challenges for conventional depolymerization methods, which often suffer from harsh conditions and poor selectivity. Electrocatalytic oxidation has emerged as a promising green strategy for the selective cleavage of lignin under mild conditions, offering a sustainable pathway to high-value aromatic chemicals. This review systematically summarizes recent advances in transition metal-based electrocatalysts for the electro-oxidative depolymerization of lignin (eLDP). It highlights and compares the design strategies and performance of noble-metal-based catalysts (e.g., Pt, Au, Ir) and earth-abundant non-noble-metal-based systems (e.g., Pb, Ni, Co). Rational catalyst design, through modulating electronic structures, coordination environments, and surface properties, can effectively promote the generation of reactive oxygen species (ROS) and facilitate the selective cleavage of key linkages (e.g., β-O-4 bonds) while suppressing the competing oxygen evolution reaction. This leads to improved yields and selectivity of valuable aromatic monomers such as phenols, aldehydes, and acids. Despite significant progress, major challenges remain in designing catalysts with simultaneously high activity, selectivity, and long-term stability, and in transitioning from model compounds to real lignin feedstocks. Future research should focus on elucidating reaction mechanisms via in situ characterization and theoretical calculations, and further optimizing catalysts through strategies like multi-metal synergy and defect engineering.