Dual-Vacancy-Induced Selective Oxidative Cleavage of C_α–C_β Bonds for the Electrocatalytic Depolymerization of Lignin

The electrocatalytic depolymerization of lignin into phenolic and carboxylic acid compounds presents a promising strategy for biomass valorization via selective C-C/C-O bond cleavage under mild conditions. However, two major challenges hinder its practical implementation: inefficient C-C bond cleavage and excessive overoxidation of the desired phenolic products. Herein, we demonstrate an engineered vacancy-rich nickel hydroxide catalyst (Ni(OH)₂-V) that achieves exceptional performance in both C_α-C_β bond cleavage of β-<i>O</i>-4 lignin linkages and suppression of phenol overoxidation. Through integrated experimental and computational analyses, this study elucidates how the synergistic introduction of cations and oxygen dual-vacancy in Ni(OH)₂-V contributes to its enhanced catalytic activity. Specifically, these dual-vacancies (1) significantly enhance the interfacial adsorption of hydroxide ions on the 2-phenoxy-1-phenylethanol (2-PPE) substrate, (2) effectively lower the energy barrier of the rate-determining step (C_α-OH → C_α═O), and (3) promote the timely desorption of phenol, thereby preventing overoxidation. The optimized catalyst achieved complete conversion of 2-PPE, yielding exceptional yields of 85.7% for phenol and 96.5% for benzoic acid at 1.40 V vs the reversible hydrogen electrode (V_RHE). These results represent 2.4-fold and 2.3-fold improvements over pristine Ni(OH)₂. Furthermore, the practical utility of Ni(OH)₂-V was validated through the depolymerization of poplar lignin and corn stover lignin, successfully yielding 14.24 and 19.54 wt % aromatic monomers. This research establishes a dual-vacancy engineering framework for precise lignin bond cleavage and offers crucial insights into the structure-activity relationship of vacancy-rich electrocatalysts for biomass valorization.