Electrocatalytic Conversion of Methane to Ethanol via Promoted •OH Generation in Aqueous Electrolyte

Converting methane (CH₄), the greenhouse gas, into high-value liquid oxygenates by an electrochemical method under mild conditions is a desired technology for establishing an energy- and environment-sustainable society. However, challenges from the competition of the oxygen evolution reaction and selectivity of the desired products still exist. Here we report the catalytic performance of Cu₂O/CuO for electrochemical conversion of methane into ethanol (CH₃CH₂OH). Density functional theory calculations demonstrated that the Cu₂O/CuO interface enables efficient CH₄ adsorption, which provides an effective pathway for methane utilization under mild conditions. Based on electrochemical studies and electron paramagnetic resonance (EPR) measurement results, it is confirmed that the activated CH₄ is converted to CH₃CH₂OH by reaction with active oxygen species (^•OH radicals) electrogenerated in situ through the water oxidation reaction over Cu₂O/CuO on the anode. Under the optimized conditions, a Faraday efficiency (FE) of 21.1% and a production rate of 126.7 μmol g_cat^–1 h^–1 at ambient pressure for CH₃CH₂OH production were obtained, and the FE remained ∼19.0% at 2.2 V cell voltage during 8 h of electrolysis. When the pressure in the bath was lifted to 4.0 bar, the production rate of 441.3 μmol g_cat^–1 h^–1 with an FE of 69.2% was obtained due to the higher solubility of CH₄ in aqueous solution.