Enhancing β-O-4 Linkage Cleavage with Ultrahigh Faradaic Efficiency via Electrochemical-Chemical Tandem Catalysis for Lignin Valorization.

Abstract

The electrocatalytic cleavage of β-O-4 linkages in lignin has gained prominence as a sustainable strategy for biomass valorization. However, its broader application remains limited by key challenges, such as low Faradaic efficiency (FE), high oxidation potentials, and limited mechanistic understanding. To address these limitations, an electrochemical-chemical tandem catalysis system is developed for the electrooxidation of 2-phenoxy-1-phenylethanol (PPE). Mechanistic investigations revealed a two-step tandem process in PPE cleavage: i) electrochemical dehydrogenation of the C_α─OH groups, followed by ii) non-electrochemical C_α─C_β bond cleavage. The improved cleavage efficiency can be primarily attributed to the accelerated electrocatalytic dehydrogenation step. To optimize the adsorption of OH^- and PPE molecules during electrocatalysis, an Au-nanoparticle-decorated CuO nanoflakes (Au/CuO) electrocatalyst is designed. Comprehensive characterization techniques demonstrated that Au nanoparticles act as active sites for C_α─OH oxidation, while the CuO substrate facilitates PPE adsorption. Notably, the Au/CuO electrode achieved high product yields of 99.2% phenol and 80.2% benzoic acid at 0.95 V_RHE, with a record-high FE of 74.7% for PPE conversion. Furthermore, the catalytic strategy was successfully extended to the depolymerization of organosolv lignin (OL). This study elucidates an electrochemical-chemical tandem mechanism for the electrocatalytic cleavage of lignin and presents an efficient electrocatalyst with high FE for lignin depolymerization.