CO and CO2Electrochemical Reduction to Methane on Cu, Ni, and Cu3Ni (211) Surfaces

Abstract

The electrocatalytic properties of Cu, Ni, and Cu0.75Ni0.25 alloy are investigated for CO and CO2 reduction to methane by density functional calculations. We show that, as the Ni content increases in Cu(1–x)Nix (211) surfaces (x = 0, 0.25, and 1), the binding energies (ΔEs) of the adsorbates involved in the reaction mechanism decrease. Linear scaling relations are known to exist between ΔEs of adsorbates binding via a C (O) atom over pure transition metal surfaces. However, we find that alloying Cu and Ni has the potential for breaking these relations for certain pairs of adsorbates. The decrease in the repulsive Coulombic interaction between the adsorbate and the charges induced on the Cu–Ni alloy surface explains the adsorption site preference. The ΔE shift with respect to pure Cu is larger for species binding through C than O. Various trends exhibited by the binding energies are understood by analyzing the chemical bonding through local density of states and charge density isosurfaces of the bare and adsorbed surfaces. The free energy profile for CO and CO2 reduction to CH4 on the alloy surface is a mix of its behavior on Cu and Ni (211). Our calculations predict that CH4 generation directly from CO reduction on Cu0.75Ni0.25 (211) can occur at an earlier applied potential than required for Cu and Ni (211) surfaces. However, it will be the opposite case for CO2 reduction to CH4.