Metal-free electrocatalytic dechlorination of chlorinated ethenes using bifunctional biochar cathode: adsorption-coupled electrocatalytic reduction mechanism

Electrochemical reductive dechlorination provides an environmentally friendly and sustainable method for the remediation of chlorinated ethenes (CEs) without chemical additives. However, the limited mass and electron transfer of commonly commercial electrodes restricts surface reactions with CEs. Herein, metal-free biochars (BCs) with high adsorption capacity (22.68∼51.32 mg/g) and conductivity (84∼303 Ω) were utilized as cathode materials for the effective dechlorination of CEs. The BC900 cathode exhibited a dechlorination efficiency of 98.14% for 10 mg/L trichloroethylene (TCE) within 24 hours, with a k_obs of 0.161 h⁻¹ under an applied potential of -1.0 V. Carbon balance and chloride form analyses indicated that nearly all C-Cl bonds were cleaved, with ethylene and acetylene identified as the primary end products. Quenching, kinetic, and electrochemical experiments demonstrated that the dechlorination process involves a direct electron transfer reduction pathway via conductive structures of BCs. Moreover, the synergistic effect on TCE dechlorination was superior to that of commercial electrocatalysts, achieving high reusability and wide adaptability in environmental water. This methodology can also be extrapolated to other CEs, including tetrachloroethylene, cis-1,2-Dichloroethylene, and vinyl chloride. These findings highlight an adsorption-coupled electrochemical reductive dechlorination mechanism for CEs, providing a theoretical foundation for the development of high-performance, biomass-based electrocatalysts in environmental applications.