Temperature-dependent research on Pt(111) and Pt(100) electrodes in aqueous H2SO4

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Abstract The temperature dependence of the under-potential deposition of hydrogen, upd H, and anion adsorption on Pt(111) and Pt(100) in aqueous H2SO4 solutions was studied by application of cyclic-voltammetry, CV. An analysis of the CV scans for Pt(111) and Pt(100) in 0.5 M aqueous H2SO4 shows that upon T increase the upd H and anion adsorption CV features shift towards less positive potentials (expressed on the SHE scale). In the case of the Pt(111) ∣ 0.05 M aqueous H2SO4 interphase, the potential regions corresponding to the upd H and the anion adsorption are separated. This constitutes the basis for determination of thermodynamic state functions of the process, namely ΔGads(Hupd), ΔSads(Hupd), and ΔHads(Hupd), as well as for elucidation of the Pt(111)–Hupd surface bond energy, EPt(111)–Hupd. The data show that for 0≤θHupd≤2/3 ΔGads(Hupd) varies from −26 to −8 kJ mol−1, ΔSads(Hupd) from −79 to −63 J mol−1 K−1, ΔHads(Hupd) from −44 to −30 kJ mol−1, and EPt(111)–Hupd from 262 to 250 kJ mol−1. An analysis of the ΔGads(Hupd) versus θHupd plots for 273≤T≤328 K reveals that the upd H follows the Frumkin isotherm and that the energy of lateral repulsion, ω, equals 27.3 kJ mol−1; it corresponds to the dimensionless parameter g equal to 11. The value of EPt(111)–Hupd falls close to that for the surface bond energy between the chemisorbed H, Hchem, and Pt(111), EPt(111)–Hchem, which is 255 kJ mol−1.