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

The temperature dependence of the under-potential deposition of hydrogen, u pd H, and anion adsorption on Pt(111) and Pt(100) in aqueous H2SO4 solution s 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 i ncrease the upd H and anion adsorption CV features shift towards less posit ive 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 fo r determination of thermodynamic state functions of the process, namely Del ta G(ads)(H-upd), Delta S-ads(H-upd), and Delta H-ads(H-upd), as well as fo r elucidation of the Pt(111)-H-upd surface bond energy, EPt(111)-Hupd. The data show that for 0 less than or equal to theta(Hupd) less than or equal t o 2/3 Delta G(ads)(H-upd) varies from -26 to -8 kJ mol(-1), Delta S-ads(H-u pd) from -79 to -63 J mol(-1) K-1, Delta H-ads(H-upd) from -44 to -30 kJ mo l(-1), and EPt(111)-Hupd from 262 to 250 kJ mol(-1). An analysis of the Del ta G(ads)(H-upd) versus theta(Hupd) plots for 273 less than or equal to T l ess than or equal to 328 K reveals that the upd H follows the Frumkin isoth erm and that the energy of lateral repulsion, omega, 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, H-chem, and Pt(111), EPt(111)-Hchem, which is 255 kJ mol(-1) . (C) 1999 Elsevier Science S.A. All rights reserved.