Enhanced Mass Activity for CO2 Electroreduction to CO via Confined Ultrasmall Au Nanoparticles

This study reports a mesoporous carbon confinement strategy for enhancing the mass activity and structural durability of Au-based catalysts toward electrochemical CO 2 reduction reaction (CO 2 RR) to CO. Glutathione-protected Au clusters were introduced into polyaniline-derived mesoporous carbon (PDMC), followed by thermal ligand removal, producing ultrasmall Au nanoparticles uniformly embedded within a conductive N-doped carbon framework. The mesoporous carbon matrix effectively restricts Au growth and suppresses nanoparticle aggregation, thereby preserving abundant low-coordinated Au surface sites while maintaining accessible channels for charge and mass transport. The optimized Au@PDMC-30 catalyst delivers a CO Faradaic efficiency of 90.0 ± 1.3% at –0.9 V vs reversible hydrogen electrode in an H-type cell and maintains stable CO production for over 24 h without obvious Au aggregation. More importantly, under flow-cell conditions, Au@PDMC-30 achieves a high CO mass activity of 1192.4 mA mg –1 , approximately twice that of commercial Au/C, demonstrating greatly improved precious-metal utilization. In situ Fourier transform infrared spectroscopy and density functional theory calculations reveal that the confined low-coordinated Au sites possess an optimized electronic structure that facilitates *COOH formation, thereby accelerating the CO 2 to CO pathway. This work highlights confinement engineering of ultrasmall noble-metal nanoparticles as an effective route to improve catalytic selectivity, durability, and mass-normalized activity for CO 2 RR.