Role of Subsurface Oxygen on Cu Surfaces for CO₂ Electrochemical Reduction

Under ambient conditions, copper with oxygen near the surface displays strengthened CO₂ and CO adsorption energies. This finding is often used to rationalize differences seen in product distributions between Cu-oxide and pure Cu electrodes during electrochemical CO₂ reduction. However, little evidence exists to confirm the presence of oxygen within first few layers of the Cu matrix under relevant experimental reducing conditions. Using density functional theory calculations, we discuss the stability of subsurface oxygen from thermodynamic and kinetic perspectives and show that under reducing potentials subsurface oxygen alone should have negligible effects on the activity of crystalline Cu.