Mechanism and Micro Kinetic Model for Electroreduction of CO<sub>2</sub> on Pd/C: The Role of Different Palladium Hydride Phases
Martijn J.W. Blom, Wim P. M. van Swaaij, Guido Mul, Sascha R.A. Kersten
Abstract
We measured the reaction kinetics of the electrochemical reduction of CO<sub>2</sub>to formate on Pd/C and evaluated several proposed mechanisms, by comparing model-described and observed rates of formation of HCOO<sup>-</sup>and H<sub>2</sub>as a function of several parameters (p<sub>H<sub>2</sub></sub>,p<sub>CO<sub>2</sub></sub>, and potential). An α-/β-hydride mechanism, based on an α-hydride phase active for CO<sub>2</sub>reduction 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 H<sub>2</sub>, this mechanism also predicted the outcome of D<sub>2</sub>isotope 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.