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We measured the reaction kinetics of the electrochemical reduction of CO2 to formate on Pd/C and evaluated several proposed mechanisms, by comparing model-described and observed rates of formation of HCOO– and H2 as a function of several parameters (p H2 , p CO2 , and potential). An α-/β-hydride mechanism, based on an α-hydride phase active for CO2 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 H2, this mechanism also predicted the outcome of D2 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.

Control over selectivity towards HCOO⁻ rather than H₂ is acquired by using elevated pressure of hydrogen during CO₂ electrolysis.

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