Insights into the Low Overpotential Electroreduction of CO₂ to CO on a Supported Gold Catalyst in an Alkaline Flow Electrolyzer

Cost competitive electroreduction of CO₂ to CO requires electrochemical systems that exhibit partial current density (j_CO) exceeding 150 mA cm^-2 at cell overpotentials (|η_cell|) less than 1 V. However, achieving such benchmarks remains difficult. Here, we report the electroreduction of CO₂ on a supported gold catalyst in an alkaline flow electrolyzer with performance levels close to the economic viability criteria. Onset of CO production occurred at cell and cathode overpotentials of just -0.25 and -0.02 V, respectively. High j_CO (∼99, 158 mA cm^-2) was obtained at low |η_cell| (∼0.70, 0.94 V) and high CO energetic efficiency (∼63.8, 49.4%). The performance was stable for at least 8 h. Additionally, the onset cathode potentials, kinetic isotope effect, and Tafel slopes indicate the low overpotential production of CO in alkaline media to be the result of a pH-independent rate-determining step (i.e., electron transfer) in contrast to a pH-dependent overall process.