Exceptional Size-Dependent Activity Enhancement in the Electroreduction of CO₂ over Au Nanoparticles

Abstract

The electrocatalytic reduction of CO2 to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but it is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. We report here the size-dependent catalytic activity of micelle-synthesized Au nanoparticles (NPs) in the size range of ∼1-8 nm for the electroreduction of CO2 to CO in 0.1 M KHCO3. A drastic increase in current density was observed with decreasing NP size, along with a decrease in Faradaic selectivity toward CO. Density functional theory calculations showed that these trends are related to the increase in the number of low-coordinated sites on small NPs, which favor the evolution of H2 over CO2 reduction to CO. We show here that the H2/CO product ratio can be specifically tailored for different industrial processes by tuning the size of the catalyst particles.

CO2 Reduction: From the Electrochemical to Photochemical Approach

“…DFT calculations disclosed that edge sites on the Au NP surface facilitated CO formation by stabilizing key intermediates such as COOH while the corner sites were active for HER owing to their increased affinity toward H. The highest selectivity observed with 8 nm Au NPs was attributed to their optimal ratio of edge sites over corner sites. Similar size dependence was also reported by Cuenya and co‐workers for Au NPs of 1–8 nm 64. As the NP size decreased, the authors observed a dramatic increase in current density and a significant decline in CO selectivity.…”

Recent Advances in Transition-Metal-Mediated Electrocatalytic CO2 Reduction: From Homogeneous to Heterogeneous Systems

“…The edge sites of the NPs are considered to accelerate CO formation, and the 8 nm Au NPs with an optimal ratio of edge sites thus offered the maximum FE up to 90% at −0.67 V vs. reversible hydrogen electrode (RHE) (Figure 1a-e). Meanwhile, similar work was also reported by Strasser's group with the sizes of Au NPs ranging from 1 nm to 8 nm [31]. As mentioned, the FE of CO declined with decreasing NP size.…”

Face the Edges: Catalytic Active Sites of Nanomaterials

“…The 8 nm Au particles with 4 nm crystallite diameter appeared to meet the demand for optimizing the edge fraction. While Cuenya group found that Au particles below 5 nm all showed significantly better performance than bulk Au, and particles larger than 5 nm were similar with bulk gold (Figure 4c,d) 74. The disparate activities in these two results may stem from different methods for measurement of size, Sun used transmission electron microscopy (TEM) while Cuenya used atomic force microscope (AFM).…”

“…Data in (c) were acquired at E = −1.2 V vs RHE. Reproduced with permission 4, 74. Copyright 2013, American Chemical Society.…”