Electrochemical CO2 Reduction on Silver – a Perspective through Electrochemical Impedance Spectroscopy

Anthropogenic carbon rise in the earth's atmosphere is the leading cause towards global warming. Electrochemical CO 2 reduction (eCO2RR) is one of the most promising sustainable pathways for the utilization and recycling of anthropogenic carbon. The current challenge in eCO2RR is to make the process more energy efficient and to drive the selectivity toward the desired products. eCO2RR normally takes place in parallel with hydrogen evolution reaction (HER). Additionally, dependent on catalyst material and potential different C-products can be obtained. The mechanistic understanding of the interplay between different reactions is still limited, since the involved reactions are characterized by faster kinetics and/or different adsorbed species as well as mass transfer dependences than the other ones. Moreover, we have recently shown that under dynamic conditions eCO2RR product selectivity towards CO can be tuned 1 . In that study, we developed a simple model and identified key kinetic parameters which govern product selectivity under dynamic conditions. The model included only the electrochemical kinetics of two parallel reactions without consideration of adsorbed species or mass transport limitations. Therefore, some of the experimental observations could not be completely explained. In such complicated cases involving different physicochemical phenomena acting in parallel at different time scales, the use of electrochemical impedance spectroscopy (EIS) to analyse the system could shed light on the understanding of the process. In this contribution, we have developed a mathematical model which couples micro-kinetics with continuum transport. At first, the model was validated under steady-state conditions. The experiments have been performed under different conditions (mass transport and buffer concentrations) on silver rotating disk electrodes and the product distribution (H 2 and CO) has been determined with the help of online gas chromatography. This model was then used to calculate EIS. Based on this approach, we present here a detailed interpretation of the EIS spectrum during eCO2RR and the features obtained at different applied electric potentials. Key insights are drawn about the role of charge and mass transport as well as adsorbed intermediates on the observed features. References 1.Miličić, T.; Sivasankaran, M.; Blumner, C.; Sorrentino, A.; Vidakovic-Koch, T., Pulsed electrolysis: explained. Faraday Discussions 2023.