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

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 C_<i>x</i>H_<i>y</i>O_<i>z</i> 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 C_<i>x</i>H_<i>y</i>O_<i>z</i> 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