CO2 Electrochemical Reduction to Methane and Methanol on Copper-Based Alloys: Theoretical Insight

Abstract

We performed a systematic investigation of CO2 electroreduction to CH4 and CH3OH on copper-based alloys stepped surfaces using density functional theory calculations associated with the standard hydrogen electrode model. We determined the correlations between CO adsorption energy and the other key CxHyOz intermediates adsorption energy, the overpotential, the limiting-potential elementary step, and selectivity to CH4, CH3OH, HCOOH, and H2. The electrode efficiency decrease by OH* poisoning and the H2 evolution is also investigated. The results demonstrate that the CO* protonation is the limiting-potential step on most surfaces, with the exception on Cu3Au and Cu3Co surfaces. In spite of the excessive strong CO* interaction on some surfaces, the overpotentials reduce when the degree of CO* adsorption energy and HCO*/COH* adsorption energy decoupling increases. The CO* adsorption energy is a good descriptor for linear scaling correlations with the other CxHyOz intermediates due to the similar charge transfer characteristics of the C–O bond in CO* and those intermediates. The formic acid production can be efficiently catalyzed on Cu3Pt, Cu3Ni, Cu3Co, and Cu3Rh surfaces. Methanol production is favorable on Cu3Pd and Cu3Pt surfaces, yet they show high overpotential (∼0.7 V). The key of methanol selectivity is CH2OH* intermediate formation favorability associated with the preference of CH2OH* protonation at the C atom over the O atom. The calculations reveal that the electroreduction activity on Cu-based alloys catalysts do not show a volcano-type relation as was previously found on pure metal catalysts.