Investigation of CO2 Electrolysis on Tin Foil by Electrochemical Impedance Spectroscopy

Abstract

The conversion of CO2 on tin catalysts via electrolysis leads to valuable chemicals like CO and formate and can help to close the carbon cycle. In the current literature, catalysts for the electrochemical CO2 reduction reaction (CO2RR) are amongst other methods characterized via electrochemical impedance spectroscopy (EIS) in terms of charge transfer resistances while neglecting the parallelly occurring hydrogen evolution reaction (HER). This may lead to an inapt assignment of the catalyst properties to the CO2RR, whereas the impedance spectrum displays features of the parasitic HER or mixed information of both the reactions. This circumstance is tackled systematically in this work by analyzing linear sweep voltammograms and impedance spectra under various experimental conditions to get more insights into the processes displayed in the respective impedance spectra. The main finding is that the observed high-frequency process displays a charge transfer reaction, which contains contributions of the HER and CO2RR and is not appropriate for evaluating catalysts for the CO2RR. This ambiguity was observed for experimental conditions where the HER or CO2RR prevailed. Additionally, equivalent circuit model (EQCM) simulations confirmed the occurrence of just one arc in the EIS spectrum for the parallelly occurring charge transfer reactions on the same electrode.