(558l) Role of Intra-Particle Grain Boundaries in CO2 Electroreduction

Recent reports have shown that grain boundaries bring in unique active sites compared to the surface facets and an interesting quantitative correlation between the inter-particle grain boundary density and catalytic performance was observed in CO2 electroreduction activity [1]. However, the correlation between the intra-particle grain boundaries and catalytic performance has never been explored. Herein, we tried to investigate the effect of intra-particle boundaries on the CO₂RR performance of Au nanocrystals as model catalysts with various grain boundary types and densities. In this regard, Au nanoparticles with single crystalline, 2-fold twinned, and 5-fold twinned crystal structure were chosen. Both the experimental and density functional theory (DFT) studies showed superior activity of 5-fold twinned gold nanoparticles comparing to others. By measuring the specific current density, we were able to notice that the number of surface boundaries is effective at low overpotentials below -0.7 V vs RHE, but the mass transfer dominated at high overpotential above -0.7 V vs RHE. DFT calculations also suggested that the reduction of CO₂ to CO is more favorable on 5-fold twinned grain boundaries than its 2-fold counterpart and single crystalline 111 surface due to a favorable stabilization of the *COOH intermediate and its ability to retard HER kinetics. Therefore, we conclude that the intra-particle grain boundaries of gold nanoparticles serve as the main active sites for CO₂ reduction reaction, and played an important role in improving the electroreduction activity of gold nanoparticles at lower overpotentials.

[1] Mariano, R. G., McKelvey, K., White, H. S., & Kanan, M. W. (2017). Selective increase in CO2 electroreduction activity at grain-boundary surface terminations. Science, 358(6367), 1187-1192.