Electrochemical CO2 Reduction to Methane by Cu Complex-Derived Catalysts in Non-Aqueous Media

Electrochemical CO2 reduction using Cu complex catalysts in non-aqueous media leads exclusively to carbon monoxide or formic acid. This study reports highly selective electrochemical CO2 reduction to methane using a 2,9-dimethyl-1,10-phenanthroline Cu2+ complex in dimethylformamide. XRD reveals the formation of a Cu complex-derived catalyst during the electrochemical testing, containing Cu and an organic phase when the electrolyte contained tetrabutylammonium cations. Insulating carbonates were preferentially deposited when the electrolyte contained alkali metal cations, leading to low Faradaic efficiency for methane. The dramatic electrolyte dependence is explained by the relative solubility of deposits in dimethylformamide under reductive potentials. The Faradaic efficiency for methane production varied from sample to sample, with underlaying variation in the morphology of the catalyst. Selective methane production using Cu complex-derived catalysts in non-aqueous media is intriguing, opening the possibility of combinatorial studies of the effect of ligand structures on product selectivity by involving ligands not soluble in water.