Integration of aprotic CO2 reduction to oxalate at a Pb catalyst into a GDE flow cell configuration

Abstract

Electrochemical CO₂ reduction to oxalic acid in aprotic solvents could be a potential pathway to produce carbon-neutral oxalic acid. One of the challenges in aprotic CO₂ reduction are the limited achievable current densities under standard conditions, despite the increased CO₂ solubility compared to aqueous applications. The application of aprotic solvents can reduce CO₂ rather selectively to oxalate, and faradaic efficiencies (FEs) of up to 80% were achieved in this study with a Pb catalyst in acetonitrile, the FE being mainly dictated by the local CO₂ concentration at the electrode. This process was integrated into a flow cell employing a two-layered carbon-free lead (Pb) gas diffusion electrode (GDE) and a sacrificial zinc (Zn) anode. With the application of this GDE the applicable current densities could be improved up to a current density of j = 80 mA cm⁻² at a FE(oxalate) = 53%, which is within the range of the highest j reported in the literature. In addition, we provide an explanation for the deactivation mechanism of metal catalysts observed in the aprotic CO₂ reduction literature. The deactivation is not related to a mass transport limitation but to cathodic corrosion observed at highly negative potential when employing quaternary ammonium supporting electrolyte cations, promoting catalyst leaching.