Assessing contaminants from ion-exchange membranes in the evaluation of aqueous electrochemical carbon dioxide reduction

In the search for new value-added products from CO2 electroreduction, it is critical that the detected species is derived from conversion of the reactants. Here we characterize contaminants from common ionomer anion- and cation-exchange membranes and demonstrate for one case how this can lead to misinterpretation of the product species by NMR spectroscopy. In particular, the membrane casting solvent N-methyl-2-pyrrolidinone (NMP) is demonstrated to be interpretable by NMR as other possible four-carbon products of the CO2 electroreduction. While the recommended commercial membrane pretreatment procedures greatly reduced the contaminant concentrations, this was not sufficient for all membrane types.