Enhancing CO<inf>2</inf> Electroreduction by Tailoring Strain and Ligand Effects in Bimetallic Copper-Rhodium and Copper-Nickel Heterostructures

We show how epitaxially grown Cu-Rh and Cu-Ni heterostructures exploit the strain effect, due to the lattice mismatch, and the ligand effect, arising from the electronic interaction between the heterolayers, to achieve improved CO2 electroreduction. In this study we have performed density functional calculations on Cui/Mj/Cu(211) sandwiched surfaces and Cui/M(211) overlayers (where M = Rh or Ni, with varied i and j monolayers). We examined the free energy profiles of the reaction mechanisms for CO2 reduction to CO and CH4. We find that in Cu1/M1/Cu(211), in which the Cu monolayer experiences only a pure ligand effect, the influence of Ni is weaker than Rh and it decreases the overpotential for CO2 reduction by ∼10-20 mV. A larger decrease (33-64 mV) in the overpotential is predicted for other sandwiched surfaces: Cu1/Ni2/Cu(211), Cu2/Rh1/Cu(211), and Cu2/Rh2/Cu(211) in which the ligand effect is weaker. In the Cu1/M(211) overlayer, Cu is affected by both the strain and ligand effects, of which the latter dominates. As the number of Cu monolayers increases from one to three, the strain effect becomes dominant in the Cu overlayers. We demonstrate that the tensile strain on Cu in Cu2-3/Rh(211) overlayers causes a significant decrease (by 86 mV) in the overpotential for CO2 electroreduction, while the compressive strain in Cu2-3/Ni(211) overlayers has an opposite effect. Furthermore, Cu2/Rh2/Cu(211) and Cu2-3/Rh(211) will also exhibit an increase in exchange current density, i.e., electrocatalytic activity for CO2 reduction. This is accompanied by a retention of selectivity for CO and CH4 over hydrogen evolution. (Graph Presented).