Extracting kinetic information on the hydrogen evolution on Pt by combining time-resolved microcalorimetry and finite-element modelling

For fast and reversible electrocatalytic reactions, like the hydrogen evolution on Pt in acidic media and in the presence of molecular H$_2$, it is very challenging to obtain reliable kinetic information from the charge-potential relationship alone. To overcome this issue, we measure the time-resolved heat flux during hydrogen evolution on polycrystalline Pt as complementary information to chronopotentiometric measurements. The interpretation of the data is based on a comparison with a finite element simulation comprising a microkinetic model coupled to mass transport. Using this approach, we estimate the exchange current density to be around 10 – 15 mA cm$^{−2}$, for both, the Tafel or the Heyrovský reaction being the rate limiting step. We also find that the coverage of the active hydrogen intermediate is low around the equilibrium potential, even in hydrogen saturated solution.