In the search for new value-added products from CO 2 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 …