Unexpected dehydrogenation pathway drives highly selective electroreduction of chloroform to methane in low-conductivity water over a Cu(OH)2 cathode.

Abstract

Chloroform (CF) is a persistent and toxic chlorinated hydrocarbon (CHC) frequently detected in groundwater, yet its complete electrochemical dechlorination under low-conductivity conditions remains challenging due to competitive hydrogen evolution and poor selectivity of conventional cathodes. Herein, we develop a simple precipitation-coated Cu(OH)2 cathode that undergoes in-situ self-activation to form a Cu(0)-Cu(OH)2 heterostructure, enabling efficient and selective electroreduction of CF to methane (CH4). At -2.0 V v.s. Ag/AgCl in a low-conductivity electrolyte (2 mM sulfate, 582 μS cm-1), the Cu(OH)2 cathode achieved 84.7% CF/CH4 conversion without chlorinated byproducts generation after 180 min. Experiments and density functional theory (DFT) revealed a dominant direct electron transfer pathway for CF dechlorination. The rate-determining step is the synergistic dehydrogenation and dehydroxylation of CF at the Cu(0)-Cu(OH)2 interface, yielding •CCl3 and H2O with a substantially lowered energy barrier. Cu(OH)2 cathode exhibits remarkable robustness against common inorganic anions, natural organic matter, and Ca2+/Mg2+-induced scaling, and maintained >75% removal over 11 cycles with extremely few Cu leaching. For the real groundwater with low conductivity (417 µS cm-1), the Cu(OH)2 cathode system removed over 96% of CHCs after five cycles during a 10-day treatment, with an energy consumption of only 3.76 × 10-3 kWh L-1, and significantly reduced acute biotoxicity. This work provides a cost-effective and sustainable electrocatalytic strategy for the remediation of CHCs in water.

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