Probing Electrocatalytic CO₂ Reduction at Individual Cu Nanostructures via Optically Targeted Electrochemical Cell Microscopy

Optically targeted electrochemical cell microscopy (OTECCM) was applied to measure electrocatalytic rates at individual Cu nanoparticles (NPs) under electrolyte conditions relevant to CO₂ reduction. The electrocatalytic responses from individual NPs were found to exhibit a wide variation in behavior, with significant NP-to-NP variations in the magnitude of electrocatalytic currents and necessary overpotentials being observed. Correlations of these quantities with metrics of NP size suggest no significant variations in the inherent electrocatalytic activity of the NPs with size. Finite element simulations of diffusion in this system demonstrate the observed diffusion-limited currents are significantly smaller than expected, attributable to the presence of a significant amount of residual ligand on the surface of the Cu NPs, which were prepared via an organic phase synthesis. The results presented here further demonstrate the promise of techniques which employ correlated optical and electrochemical measurements, such as OTECCM, for studying electrocatalysis at individual NPs.