Thermodynamic properties of hydrogen-water adsorption at terraces and steps of Pt(111) vicinal surface electrodes

- Hydrogen and water adsorptions on Pt(111) vicinal surfaces have been studied.
- Thermodynamic properties at Pt stepped surfaces/water interface were calculated.
- Adsorption at steps does not depend on the step density.
- Adsorption at terraces depends on the step density.

In this work, the effect of temperature on the adsorption states of Pt(111) vicinal surface electrodes in perchloric acid is studied through a thermodynamic analysis. The method allows calculating thermodynamic properties of the interface. In this framework, the concept of the generalized isotherm and the statistical thermodynamics description are applied to calculate formal entropies, enthalpies and Gibbs energies, ΔG¯i0, of the adsorption processes at two-dimensional terraces and one-dimensional steps. These values are compared with data from literature. Additionally, the effect of the step density on ΔG¯i0 and on the lateral interactions between adsorbed species, ωij, at terraces and steps is also determined. Calculated ΔG¯i0, entropies and enthalpies are almost temperature-independent, especially at steps, but they depend on the step orientation. In contrast, ΔG¯i0 and ωij at terraces depend on the step density, following a linear tendency for terrace lengths larger than 5 atoms. However, while ΔG¯i0 increases with the step density, ωij decreases. Results were explained by considering the modification in the energetic surface balance by hydrogen, Hads, and water, H2Oads, co-adsorption on the electrode, which in turn determines the whole adsorption processes on terraces and steps.

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