Monodisperse Au Nanoparticles for Selective Electrocatalytic Reduction of CO₂ to CO

TLDR

Density functional theory calculations suggest that Au nanoparticle surfaces with more edge sites than corner sites stabilize COOH* intermediates, favoring CO evolution over H₂ production. The study reports the selective electrocatalytic reduction of CO₂ to CO on gold nanoparticles dispersed in 0.5 M KHCO₃ at 25 °C. The authors employed monodisperse Au nanoparticles and further stabilized COOH* intermediates by embedding the particles in a butyl‑3‑methylimidazolium hexafluorophosphate matrix to enhance activity and selectivity. The 8‑nm Au nanoparticles achieved a maximum Faradaic efficiency of 90 % at –0.67 V vs RHE, and when embedded in the ionic liquid matrix the activity reached 3 A g⁻¹ with 97 % FE at –0.52 V, underscoring the promise of monodisperse Au NPs for selective CO₂ reduction to CO.

Abstract

We report selective electrocatalytic reduction of carbon dioxide to carbon monoxide on gold nanoparticles (NPs) in 0.5 M KHCO3 at 25 °C. Among monodisperse 4, 6, 8, and 10 nm NPs tested, the 8 nm Au NPs show the maximum Faradaic efficiency (FE) (up to 90% at -0.67 V vs reversible hydrogen electrode, RHE). Density functional theory calculations suggest that more edge sites (active for CO evolution) than corner sites (active for the competitive H2 evolution reaction) on the Au NP surface facilitates the stabilization of the reduction intermediates, such as COOH*, and the formation of CO. This mechanism is further supported by the fact that Au NPs embedded in a matrix of butyl-3-methylimidazolium hexafluorophosphate for more efficient COOH* stabilization exhibit even higher reaction activity (3 A/g mass activity) and selectivity (97% FE) at -0.52 V (vs RHE). The work demonstrates the great potentials of using monodisperse Au NPs to optimize the available reaction intermediate binding sites for efficient and selective electrocatalytic reduction of CO2 to CO.