Pd-Catalyzed Electrohydrogenation of Carbon Dioxide to Formate: High Mass Activity at Low Overpotential and Identification of the Deactivation Pathway

Electrochemical reduction of CO2 to formate (HCO2–) powered by renewable electricity is a possible carbon-negative alternative to synthesizing formate from fossil fuels. This process is energetically inefficient because >1 V of overpotential is required for CO2 reduction to HCO2– on the metals currently used as cathodic catalysts. Pd reduces CO2 to HCO2– with no overpotential, but this activity has previously been limited to low synthesis rates and plagued by an unidentified deactivation pathway. Here we show that Pd nanoparticles dispersed on a carbon support reach high mass activities (50–80 mA HCO2– synthesis per mg Pd) when driven by less than 200 mV of overpotential in aqueous bicarbonate solutions. Electrokinetic measurements are consistent with a mechanism in which the rate-determining step is the addition of electrochemically generated surface adsorbed hydrogen to CO2 (i.e., electrohydrogenation). The electrodes deactivate over the course of several hours because of a minor pathway that forms CO. Activity is recovered, however, by removing CO with brief air exposure.