Examining the Oxygen Tolerance of Mn(bpy)(CO)3Br in Electrochemical CO2 Conversion to CO and Formic Acid

CO2 capture and utilization requires the development of highly selective catalysts that convert low concentration CO2 into valuable chemicals. Direct air capture (DAC) CO2 contains up to 10% of oxygen as an impurity, which is a sincere competitor to electrochemical CO2 reduction reaction (CO2RR) due to its favourable thermodynamics. In the best case, the competing O2 reduction reaction (ORR) leads to lower Faradaic efficiencies of CO2RR; and in the worst case, reactive oxygen species (ROS) are generated that lead to catalyst degradation. To circumvent this competing reaction, a catalyst featuring a kinetic advantage for CO2RR is required. However, state-of-the-art CO2 reduction catalysts are rarely explored under dilute or impure conditions. Herein, we investigate the intrinsic reactivity of a molecular manganese-based CO2RR catalyst in DAC-mimicking conditions. Depending on reaction conditions, the catalyst can follow two different mechanisms, which selectively form either CO or formic acid (FA). The oxygen tolerance of the catalyst was found to be dependent on the reaction mechanism: the first step of the CO selective mechanism is CO2 binding, which is faster than O2 binding, leading to an intrinsically oxygen tolerant mechanism; however, the FA selective mechanism goes via a manganese-hydride intermediate which facilitates ORR at the metal-centre.