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

Abstract

Abstract:In this work, the effect of the 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, ∆ 0 , 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∆ 0 and on the lateral interactions between adsorbed species, ωij, at terraces and steps is also determined. Calculated ∆ 0 , entropies and enthalpies are almost temperature-independent, especially at steps, but they depend on the step orientation. In contrast, ∆ 0 and ωij at terraces depend on the step density, following a linear tendency for terrace lengths larger than 5 atoms. However, while ∆ 0 increases with the step density, ωij decreases. Results were explaining 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.

The voltammetry of surfaces vicinal to Pt{110}: Structural complexity simplified by CO cooling

“…This happens with Pt(111) and Pt(100) in alkaline media [34]. Also, it should be noted that water interactions change with potential [35,36].…”

Effect of pH and Water Structure on the Oxygen Reduction Reaction on platinum electrodes

“…Some hypotheses have been proposed to explain this phenomenon, e.g. a mixed contribution of OH and O in this adsorption process [57], changes in the lateral interaction with pH [58] or the oxidative adsorption of water on the step edges [59]. To sum up, the electrochemical interface changes as the pH value is modified for all the studied orientations, and this can have consequences for the ORR activity.…”

First Principles Simulations of Cyclic Voltammograms on Stepped Pt(553) and Pt(533) Electrode Surfaces

“…[5] Recent work from Gómez-Marín et al suggested that near surface water may have a significant effect on the adsorption of hydrogen at platinum steps and that the changing electric field near the surface with pH may alter the structure and interaction of near surface water with adsorbed hydrogen. [19] Schwarz et al used DFT to suggest that water binds very strongly to platinum step sites, such that competitive adsorption of hydrogen and water occurs at low potentials. [20] They further show that a significant amount of charge can transfer to water adsorbed at step sites, which would give a nonunity electrosorption valency and explain a non-Nernstian shift with pH.…”