Papers by Author: Lj.M. Vračar

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Authors: M.D. Obradović, B.N. Grgur, Lj.M. Vračar
Abstract: Underpotential deposition of nickel and hydrogen on polycrystalline platinum in weak acid and neutral solutions (3.5 ≤ pH ≤ 7.0), with and without Ni2+-ions, has been examined using cyclic voltammetric technique in the range of temperature from 274 to 313 K. The nickel and hydrogen ad-atom surface coverages were calculated from the voltammetric adsorption and desorption charges. The Temkin isotherm was fitted for both underpotential depositions, and thermodynamic adsorption parameters were calculated for both atoms. The value of the bonding energy between hydrogen and surface in the presence of underpotentially deposited nickel was calculated and found to amount to 287 kJ mol-1, which is 40 kJ mol-1 stronger bond than the same of pure platinum. The presence of nickel on the surface facilitates interfacial transfer of hydrogen into the metal bulk and consequent hydride formation significant in design of hydrogen based fuel cells.
Authors: Lj.M. Vračar, N. Krstajić, N. Elezović
Abstract: The underpotential deposition of hydrogen was studied in 0.5 mol dm-3 HClO4 solution on an electrode based on Ebonex-supported platinum electrocatalyst spread on rotation Au disk electrode (Ebonex/Pt). Pt catalyst was prepared by the impregnation method from 2-propanol solution of Pt(NH3)2(NO2)2 and Ebonex powder. Ebonex support (nonstoichiometric mixture of titanium oxides) was characterized by: X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and BET techniques. The synthesized catalyst was analyzed by TEM technique. Voltammetric profiles at the Ebonex/Pt catalyst surface in 0.5 mol dm-3 HClO4 aqueous solution obtained at different temperatures with the evaluation of the temperature effect on the reversible adsorption of the Hupd state are presented and the thermodynamic state functions for H adatom adsorption process are calculated. The chemisorptive energy strength of the Ebonex/Pt-H state is estimated in order to establish the relationship between the surface structure and the electrocatalytic activity of Ebonex/Pt electrode and compare it to the one for smooth polycrystalline Pt.
Authors: Lj.M. Gajić-Krstajić, T.Lj. Trišović, B. Babić, Lj.M. Vračar
Abstract: The kinetics of oxygen reduction (ORR) on carbon cryogel supported Pt nanoparticles (Pt / C) in acid solution was studied using the rotating disk electrode technique. This electrocatalyst was prepared by a modified polyol synthesis method and characterized by transmission electron microscopies. The kinetics of ORR shows a significant enhancement at Pt nanoparticle surfaces as compared with the same reaction on polycrystalline Pt surface. The four-electron reduction, with a first-charge transfer-rate determining step, has been found to be operative. However, the specific activity of the Pt / C is similar to that of the polycrystalline Pt electrocatalyst.
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