Barriers of Electrochemical CO₂ Reduction on Transition Metals

Theoretical investigations of electrochemical CO₂ reduction have received increasing interest due its potential impact on renewable energy storage. We use density functional theory with an explicit solvent model of the electrochemical interface to calculate activation energy barriers for various proton-electron transfer elementary reactions steps for CO₂ reduction on Au, Cu, and Pt surfaces. We find the protonation of unhydrogenated oxygen to be trivial compared to the protonation of carbon and R-OH species, which induces C-O scission. Our revised free energy diagram for the reduction of CO₂ to methane on Cu(211) includes these observations and suggests that the dominant pathway includes ∗CHOH and ∗CH as intermediates rather than ∗OCH₃.