Tuned Chemical Bonding Ability of Au at Grain Boundaries for Enhanced Electrochemical CO2 Reduction

Abstract

Electrochemical carbon dioxide (CO2) reduction is an emerging technology for efficiently recycling CO, into fuel, and many studies of this reaction are focused on developing advanced catalysts with high activity, selectivity, and durability. Of these catalysts, oxide-derived metal nanoparticles, which are prepared by reducing a metal oxide, have received considerable attention due to their catalytic properties. However, the mechanism of the nanoparticles' activity enhancement is not well-understood. Recently, it was discovered that the catalytic activity is quantitatively correlated to the surface density of grain boundaries (GBs), implying that GBs are mechanistically important in electrochemical CO2 reduction. Here, using extensive density functional theory (DFT) calculations modeling the atomistic structure of GBs on the Au (111) surface, we suggest a mechanism of electrochemical CO2 reduction to CO mediated by GBs; the broken local spatial symmetry near a GB tunes the Au metal-to-adsorbate pi-backbonding ability, thereby stabilizing the key COOH intermediate. This stabilization leads to a decrease of similar to 200 mV in the overpotential and a change in the rate-determining step to the second reduction step, of which are consistent with previous experimental observations. The atomistic and electronic details of the mechanistic role of GBs during electrochemical CO2 reduction presented in this work demonstrate the structure-activity relationship of atomically disordered metastable structures in catalytic applications