The direct interconversion of chemical and electrical energy is essential for the storage of electricity from renewables, a key component of a sustainable energy economy. The electrochemical CO₂ reduction reaction (CO₂RR) to value-added carbonaceous products presents an attractive route to sustainable chemical fuel production using renewable electricity as the energy input. Although the rates and selectivity of the CO₂RR are known to be strongly influenced by the identify of alkali cations in the medium, 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. To decouple these two possible origins for cation effects on the CO₂RR, we designed a system to investigate catalysis solely in the presence of an electrostatic promotion mode. Herein, we show that CO₂ reduction can occur in the presence of weakly coordinating tetraalkylammonium cations and that the addition of low millimolar concentrations of alkali ions leads to no enhancement in CO₂RR rates, indicating that weakly coordinating organic cations can facilitate CO₂ reduction to CO in the absence of alkali metal cations. These findings suggest that coordinative interactions between the electrolyte cation and surface-bound intermediates are not required for CO₂ activation and supports a paradigmatic shift in electrolyte design rules to include water-soluble organic cation salts as potential supporting electrolytes for CO₂ electrolysis.

<b>Left:</b> Depiction of electrostatic versus coordinative interactions proposed to explain the origin of cation effects on CO<sub>2</sub> reduction. Metal cations are capable of facilitating CO<sub>2</sub> activation via both types of interaction, even in the presence of organic surfactant or ionomer additives. <b>Right:</b> In this work, organic cations are used to study CO<sub>2</sub> reduction in the absence of coordinating ions.

Left: Depiction of electrostatic versus coordinative interactions proposed to explain the origin of cation effects on CO₂ reduction. Metal cations are capable of facilitating CO₂ activation via both types of interaction, even in the presence of organic surfactant or ionomer additives. Right: In this work, organic cations are used to study CO₂ reduction in the absence of coordinating ions.

Sophia Weng

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