Tailoring the Interfacial Water Structure by Electrolyte Engineering for Selective Electrocatalytic Reduction of Carbon Dioxide

Engineering aqueous electrolytes with low amounts ofadditivesto achieve a tunable CO2 reduction product is an underexploredterritory in electrocatalysis. Here, we show the enhancement of theFaradaic efficiency (FE) of CO2 reduction to CO on unmodifiedpolycrystalline gold from similar to 67 to similar to 94% by the additionof up to 15 mol % of N,N-dimethylformamide(DMF) to an aqueous electrolyte. The role of electrolyte structuremodification near the electrode-electrolyte interface was studiedusing in situ surface-enhanced infrared absorptionspectroscopy in attenuated total reflection mode (ATR-SEIRAS). Inaddition to the expected detection of the adsorbed CO (COad) intermediate present on the Au surface, in both the linearly bondedand bridge-bonded forms, we observed changes in the structure of interfacialwater induced by the addition of DMF. The changes in the water stretchingband and the DMF carbonyl band indicate an increase in the stronglyhydrogen-bonded DMF-water pairs with increasingly negativepotential near the interface in the presence of DMF. We hold thisinterfacial water structure modification by DMF responsible for increasingthe CO2RR FE and decreasing the competing hydrogen evolution reaction(HER). Furthermore, the suppression of the HER is observed in otherelectrolytes and also when platinum was used as an electrode and hencecan be a potential method for increasing the product selectivity ofcomplex electrocatalytic reactions.