Multimolar CO2 concentrations are achieved in acetonitrile solutions containing supporting electrolyte at relatively mild CO2 pressures (<5 MPa) and ambient temperature. Such CO2‐rich, electrolyte‐containing solutions are termed as CO2‐eXpanded Electrolytes (CXEs) because significant volumetric expansion of the liquid phase accompanies CO2 dissolution. Cathodic polarization of a model polycrystalline gold electrode‐catalyst in CXE media enhances CO2 to CO conversion rates by up to an order of magnitude compared with those attainable at near‐ambient pressures, without loss of selectivity. The observed catalytic process intensification stems primarily from markedly increased CO2 availability. However, a non‐monotonic correlation between the dissolved CO2 concentration and catalytic activity is observed, with an optimum occurring at approximately 5 m CO2 concentration. At the highest applied CO2 pressures, catalysis is significantly attenuated despite higher CO2 concentrations and improved mass‐transport characteristics, attributed in part to increased solution resistance. These results reveal that pressure‐tunable CXE media can significantly intensify CO2 reduction rates over known electrocatalysts by alleviating substrate starvation, with CO2 pressure as a crucial variable for optimizing the efficiency of electrocatalytic CO2 conversion.

Modeling and simulation reveal the mechanistic basis for the pressure-tunable rates of CO2 reduction at elevated pressures of CO2.

The electrochemically-formed In0–In2O3 composite changes the selectivity of CO2 reduction on In from formate to CO at relatively low overpotentials.

Electrochemical studies of CO2 conversion by molecular catalysts are typically carried out in a narrow range of near‐ambient CO2 pressures wherein low CO2 solubilities in the liquid phase can limit the rate of CO2 reduction. In this study, five‐fold rate enhancements are enabled by pairing CO2‐expanded electrolytes (CXEs), a class of media that accommodate multimolar concentrations of CO2 in organic solvents at modest pressures, with a homogeneous molecular electrocatalyst, [Re(CO)3(bpy)Cl] (1, bpy=2,2′‐bipyridyl). Analysis of cyclic voltammetry data reveals pressure‐tunable rate behavior, with first‐order kinetics at moderate CO2 pressures giving way to zero‐order kinetics at higher pressures. The significant enhancement in the space‐time yield of CO demonstrates that CXEs offer a simple yet powerful strategy for unlocking the intrinsic potential of molecular catalysts by mitigating CO2 solubility limitations commonly encountered in conventional liquid electrolytes. Moreover, our findings reveal that 1, a workhorse molecular catalyst, performs with intrinsic kinetic behavior, which is competitive with fast enzymes under optimal conditions in CXEs.