Specificity of the UPD of H to the structure of highly dispersed Pt on carbon support

Home-made carbon cryogel synthesized by sol–gel polycondensation and freeze-drying is used as support for preparation of highly dispersed Pt catalyst that is made by a modified polyol synthesis method in an ethylene glycol (EG) solution. Specific surface area of carbon support and Pt/C catalyst is determined from nitrogen adsorption isotherm. The adsorption isotherm demonstrates a significant mesoporosity of carbon support. Specific surface area of the carbon support, calculated by the BET equation, is found to be 573 m 2 g - 1 . diffraction (XRD) results demonstrate a successful reduction of the Pt precursor to its metallic form, and transmission electron microscopy (TEM) images show very uniform Pt particle size distribution with mean particle size of about 2.7 ± 0.7 nm of the catalyst. iodynamic studies of the underpotential deposition of hydrogen ( H upd ) on Pt/C electrode in 0.5 mol dm - 3 HClO 4 aqueous solution in the temperature range from 274 to 318 K are made, and thermodynamic state functions for the hydrogen adsorption are determined. perimental results are analyzed assuming linear variation of the Gibbs energy of adsorption versus θ H upd on the basis of the surface heterogeneity. The increase of Δ G H upd θ with the surface coverage indicates the repulsive interactions between H upd adatoms. From the temperature dependence of the Gibbs energy of adsorption, the enthalpy and the entropy of adsorption are calculated. The values of these functions are determined to be Δ H H upd θ = 0 = - 5.6 kJ mol - 1 and Δ S H upd θ = 0 = 69.1 J mol - 1 K - 1 . The value of Δ H H upd θ allows determinations of the bond energy between electrode surface and H upd that is found to be E Pt – H = 223 kJ mol - 1 for θ = 0 .