Temperature effects on platinum single-crystal electrodes

Abstract

This work reviews three different approaches for the study of temperature effects on the platinum single crystal | solution interphase. First, the method of analysis of temperature dependent voltammetric data with the help of a generalized isotherm is described and illustrated for the case of adsorbed hydrogen and OH species on Pt(111) in 0.1 M HClO 4 . This method of analysis allows a detailed evaluation of the thermo dynamic data of charge transfer adsorbed species, namely, the standard molar Gibbs energy, enthalpy and entropy of adsorption and the magnitude of the lateral interaction between adsorbed species. However, a number of assumptions are involved in the application of a generalized isotherm, namely, the assumption of a Langmuirian configurational term and an arbitrary separation of capacitive and faradaic processes. The sec ond approach described here overcomes these assumptions, since it employs Gibbs thermodynamic equa tions for interphaces to describe temperature effects on electrosorption processes including those in which charge transfer is allowed. This approach allows evaluation of the entropy of formation of the interphase, being defined as the difference in entropy of the components of the interphase when they are forming it and when they are in the bulk phases. This method of analysis is illustrated through the evaluation of the entropy of formation of the interphase for Pt(111) in 0.1 M HClO 4 . Finally, it is shown that temperature effects on interfacial processes can also be studied by means of the application of a fast temperature perturbation. This approach opens the possibility to separate the effect of temperature on the different components of the inter phase. The fast temperature perturbation is usually achieved with short laser pulses, and hence the method is called the laser induced temperature jump method. This approach is illustrated here for the case of Pt(111) in 1 mM HClO 4 + 0.1 M KClO 4 , and it is shown that the corresponding laser induced transients provide direct evidence on the reorientation of the interfacial water network.

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

“…Later, works employing more precise methods to characterize the interface, like the analysis based on the electrocapillary equation [20,21,24], reported a good agreement with results from the generalized isotherm strategy [15,17].…”

“…Commonly, they have been attributed to Hads on step sites [11,12,14], because peak potentials are constant and charge densities linearly increase with step density, in good agreement with a process where one electron is exchanged per step atom [11][12][13][14]. However, because of their unusual pHdependent shift of 50 mV NHE/pH unit [22,33], and their sharp shape, which can be only modeled by assuming net attractive interactions between adsorbed species [30] in contrast to repulsive Hads lateral interactions on {111} terraces [15,17,20,24], it has been recently also suggested that these peaks at 0.13V and 0.28 V could be caused by competitive co-adsorption of OHads, or even adsorbed oxygen, Oads, from water dissociation at steps, through a more complex reaction scheme [33]:…”

“…Two different step sites can be distinguished: those with {100} geometry and those with {110} geometry. Therefore, the study of the influence of steps, with different orientation, upon the electrochemical reactivity has become a relevant area [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25].However, the understanding at microscopic scale of phenomena underneath voltammetric profiles, the distinction among different processes that could contribute to the voltammetric features and their dependence on various experimental parameters, is still far from being complete, and more work is still necessary to fully understand these simple signatures. In this sense, temperature dependence analysis of voltammetric profiles provides unique information about the electrochemical interface.…”

On the activation energy of the formic acid oxidation reaction on platinum electrodes

“…For the different experiments, the reference electrode was kept at room temperature (298 K). To transform the direct potential reading to the RHE scale at 298 K values, the direct potential reading should be corrected for the thermodiffusion potential using the procedure explained in reference [21]. Solutions were prepared from sulfuric acid, perchloric acid, sodium perchlorate, formic acid (Merck suprapur in all cases) and ultrapure water from Elga.…”

“…Larger differences are observed on the Pt(111) electrode, for which, a diminution of the activation energy is observed around 0.6 V in sulfuric acid solutions. The diminution should be then related to the changes in the sulfate coverage, since, in this region the sulfate layer rearranges to reach the maximum coverage [21].…”