Electrocatalytic CO₂ reduction on earth abundant 2D Mo₂C and Ti₃C₂ MXenes

Mo₂C and Ti₃C₂ MXenes were investigated as earth-abundant electrocatalyts for the CO₂ reduction reaction (CO₂RR). Mo₂C and Ti₃C₂ exhibited faradaic efficiencies of 90% (250 mV overpotential) and 65% (650 mV overpotential), respectively, for the reduction of CO₂ to CO in acetonitrile using an ionic liquid electrolyte. The use of ionic liquid 1-ethyl-2-methylimidazolium tetrafluoroborate as an electrolyte in organic solvent suppressed the competing hydrogen evolution reaction. Density functional theory (DFT) calculations suggested that the catalytic active sites are oxygen vacancy sites on both MXene surfaces. Also, a spontaneous dissociation of adsorbed COOH species to a water molecule and adsorbed CO on Mo₂C promote the CO₂RR.