Enhancing Molecular Electrocatalysis of CO2 Reduction with Pressure-Tunable CO2 -Expanded Electrolytes

Abstract

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.

Keywords: CO2 expanded liquids; catalysis; electrochemistry; redox chemistry; renewable energy.