Assessing the activity and stability of Cu2O/SnO2-based gas diffusion electrodes for the CO2 conversion in different electrolytes: Bicarbonate vs. Ionic Liquid/Acetonitrile

Gas diffusion electrodes (GDEs) are key components for enabling the deployment of electrochemical CO2 conversion on a large scale. Most studies focused on optimising the GDEs’ performance in aqueous electrolytes, while their use with non-conventional electrolytes integrating CO2 capture and co-catalytic conversion abilities is missing in the literature. Herein, the performance of a newly designed Cu2O/SnO2-based GDE was investigated for the first time in a continuous-feed flow cell at a 10.2 cm2 scale, both in an aqueous KHCO3 medium and in a binary ionic liquid-organic solvent solution. Outstanding catalyst stability and selectivity, i.e. Faradaic efficiency to CO (FECO) from 84 to 90 % in the aqueous electrolyte, was demonstrated at current densities between −20 and −100 mA cm−2, establishing a benchmark for the CO2 reduction to CO on a Cu-based GDE. In comparison, a FECO of 35 % (CO/H2 ratio > 3) was reached at –20 mA cm−2 with 1-Butyl-3-methylimidazolium triflate ([BMIM][TfO]) in acetonitrile (ACN). Still, stability issues and a performance drop were faced during operation in this aprotic media. Molecular dynamics simulations and ex-situ physical–chemical characterisation assessed that the changes in the catalyst/GDE structure and electrolyte properties started with the displacement of Cu surface atoms from their equilibrium position by ACN molecules, which promotes the subsequent dissolution of Cu in the presence of [BMIM][TfO] molecules. Our findings highlight the significant influence of electrolyte composition on catalyst surface transformation and performance during the reaction. This work unveils critical issues for the practical application of IL-based electrolytes as co-catalysts and CO2 capture media for CO2 electrochemical conversion systems and proposes some mitigation strategies.