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

Electrochemical carbon dioxide (CO₂) reduction is an emerging technology for efficiently recycling CO₂ 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 π-backbonding ability, thereby stabilizing the key COOH intermediate. This stabilization leads to a decrease of ∼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