Tetraethylammonium Cation Activates Fe for Selective Electroreduction of CO2 to Oxalate

Abstract

The strong binding energy of CO on iron surfaces has rendered Fe electrodes as poor electrochemical CO₂ reduction (eCO2R) catalysts, predominantly producing hydrogen. Recent studies on tuning the microenvironment near the catalyst surfaces by tuning the local electric field in nonaqueous environments have been shown to promote eCO2R by facilitating the CO₂ activation step. Herein, the use of tetraethylammonium (TEA) cation to tune the electric field on Fe surfaces, such that it leads to the formation of industrially relevant oxalates (C₂ products), is reported. At optimal cation concentrations, the developed eCO2R system achieves 25 mA cm⁻² of current density and Faradaic Efficiencies up to 75% toward oxalate. Furthermore, in situ attenuated total reflectance Fourier transform infrared spectroscopy indicates the presence of surface-adsorbed TEA cations and other species on the Fe surfaces, leading to the well-known outer-sphere mechanism of electron transfer during eCO2R. The employment of Fe, along with microenvironment tuning, not only demonstrates high catalytic performance but also provides a safer and more sustainable alternative to toxic catalysts such as Pb that dominate the nonaqueous eCO₂R literature. These findings pave the way for further optimization and scale-up of the process, offering a viable route for sustainable chemical production and CO₂ mitigation.