Mechanism and Micro Kinetic Model for Electroreduction of CO2 on Pd/C: The Role of Different Palladium Hydride Phases

We measured the reaction kinetics of the electrochemical reduction of CO2to formate on Pd/C and evaluated several proposed mechanisms, by comparing model-described and observed rates of formation of HCOO-and H2as a function of several parameters (pH2,pCO2, and potential). An α-/β-hydride mechanism, based on an α-hydride phase active for CO2reduction and a β-hydride Pd-phase active for hydrogen evolution, described the experimental data of our and other laboratories reported in the literature satisfactorily. After parametrization, using a data set including only H2, this mechanism also predicted the outcome of D2isotope labeling experiments correctly. Analyses of the results indicate that the α-/β-hydride ratio and hydride formation rate are key factors affecting the formate production rate and the selectivity, thereby identifying areas for further (spectroscopic) studies and mechanism validation.