Ar-plasma activated Au film with under-coordinated facet for enhanced and sustainable CO₂ reduction to CO

Au exhibits special properties in electrocatalytically converting CO₂ into CO, wherein it is challenging to improve the activity and selectivity of CO production due to concurrent H₂ evolution reaction. Since nanostructured Au films with under-coordinated facets can facilitate catalytic performance in selective CO₂ reduction, herein, we develop a facile method to bombard the Au films using Ar plasma to induce the surface nanostructure, which exhibit greatly enhanced activity and selectivity of reducing CO₂ to CO, with a Si solar cell as the power source in order to achieve green conversion of CO₂. A high CO Faradaic efficiency of 81.4 % is achieved, with a cathodic CO energy efficiency of 58.0 % at –0.65 V vs RHE. It is found that the Ar-plasma treatment can create new active sites of under-coordinated facet with open structure, Au(311), lower surface work function, and increase the electrochemical surface area of Au film. Density functional theory calculations reveal that the Gibbs free energy required for COOH* formation is lower on the open Au(311) facet than that on the closely-packed Au(111), accounting for greater ability of the CO₂ activation on Au(311) facet. All these are favorable for enhanced CO₂ conversion to CO.