Electrochemical CO2 Reduction on Au Cluster-based Electrodes: Investigating the Role of Nafion Ionomer

Abstract

The performance of electrocatalytic CO2 reduction (CO2RR) depends not only on the catalytic material but also on the neighbouring chemical environment around the active sites. The surrounding local environment can perturb the electronic properties of active sites and alter the adsorption/desorption behaviour of reactant/intermediate/product, thus changing CO2RR characteristics. Herein, we studied electrochemical reduction of CO2 onto supported atomically precise [Au9(PPh3)8](NO3)3 clusters and observed an unusual increase in catalytic activity over time. Additionally, electrochemical activation of the electrodes by applying a more negative potential was found to improve activity of the electrode. Investigations using UV–vis and X-ray absorption spectroscopy revealed that these observations may be attributed to the interaction of the Nafion ionomer with the catalytic Au9 clusters. These interactions may cause partial blocking of the Au9 active sites, and the prolonged application of negative potentials leads to favourable interface reconstructions. In addition, a method was developed to minimise the interaction between the Au9 clusters and Nafion ionomer by first depositing a layer of carbon black followed by dropcasting the active catalyst. Our study highlights that polymeric binders modulate the electronic properties of the electrocatalysts, which can change the product distribution during CO2 electrolysis.