Weakly Coordinating Organic Cations are Intrinsically Capable of Supporting CO2 Reduction Catalysis

The rates and selectivity of electrochemical CO2 reduction are known to be strongly influenced by the identity of alkali cations in the medium. However, experimentally, it remains unclear whether cation effects arise predominantly from coordinative stabilization of surface intermediates or from changes in the mean-field electrostatic environment at the interface. Herein, we show that Au- and Ag-catalyzed CO2 reduction can occur in the presence of weakly coordinating (poly)tetraalkylammonium cations. Through competition experiments in which the catalytic activity of Au was monitored as a function of the ratio of the organic to metal cation, we identify regimes in which the organic cation exclusively controls CO2 reduction selectivity and activity. We observe substantial CO production in this regime, suggesting that CO2 reduction catalysis can occur in the absence of Lewis acidic cations and thus, coordinative interactions between the electrolyte cations and surface-bound intermediates are not required for CO2 activation. For both Au and Ag, we find that tetraalkylammonium cations support catalytic activity for CO2 reduction on par with alkali metal cations, but with distinct cation activity trends between Au and Ag. These findings support a revision in electrolyte design rules to include water-soluble organic cation salts as potential supporting electrolytes for CO2 electrolysis.