Recycling electroplating sludge to produce sustainable electrocatalysts for the efficient conversion of carbon dioxide in a microbial electrolysis cell

Electrochemical reduction is one of the most promising methods for converting carbon dioxide (CO2) into valuable chemicals, but its disadvantages include its low efficiency and need for a high electrode overpotential. In this study, a novel catalyst derived from thermally treated electroplating sludge (TES) was investigated for use in the electrochemical reduction of CO2 by means of full utilization of the chemical features of electroplating sludge. This new catalyst can reduce CO2 with a peak potential of −0.3 V (versus SCE), as measured using a linear sweep voltammogram, suggesting its' good electrocatalytic activity. Furthermore, this catalyst is feasible for use in converting CO2 in a microbial electrolysis cell; the main products were methane, ethylene, carbon monoxide and acetate with faraday efficiencies of 37.3%, 25.9%, 7.8% and 6.8% at an external potential of 0.6 V, respectively. The catalytic performance of the TES-based catalyst is much better than that of catalysts derived from municipal and dyeing sewage sludge. Electrokinetic data and electrochemical in situ infrared spectra reveal that the notable reactivity for CO2 reduction may arise from a competition between the slow combination of pairs of CO2·− ions and the fast kinetic activation toward protonation on the metal or metal oxide surface of the TES. This study presents a new approach to recycling solid waste to produce an inexpensive catalyst that performs CO2 conversion well.

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