The HER performance of colloidal Pt nanoparticles incorporated in polyaniline

Dc polarization curves and admittance spectra of PANI electrodes having incorporated Pt nanoparticles are recorded at H-2 evolution reaction (HER) potentials, and analyzed in order to determine the kinetic parameters of the process. The physical and equivalent circuit models for the H-2 evolution process in aqueous solutions of hydrochloric acid are found similar for PANI with Pt nanoparticles and bulk Pt electrodes. The coverage of the electrode by H atoms, and the rate constants for the two kinetic steps involved in the process of H-2 evolution at Pt nanoparticles incorporated with a thin polyaniline film have been determined. The rate constants for the forward Volmer and Heyrovsky reactions are 2 x 10(-11) and 3 x 10(-11) mol s(-1) cm(-2), respectively. The coverage of the electrode by adsorbed hydrogen atoms in the Tafel region is ca. 0.5 and the double layer capacitance decreases with overpotential from 18 to 11 mu F cm(-2) (over the range of -0.2 to -0.6 V vs. SCE). Thus, the electrochemically available area of the catalytically active surface of the Pt-polyaniline composite electrode is only slightly smaller than the geometrical ai ea of the corresponding bulk Pt electrode. Furthermore, Some effects due to the electropolymerization and metal electrodeposition procedures on the electrode properties of the Pt-particles incorporated with thin films of polyaniline are presented. The low overpotential admittance data show deviations from predictions of the classical kinetic model of HER. Together with the Tafel region results, this may indicate specific transport properties and/or nonequivalent adsorption sites for adsorbed H. (C) 2000 Elsevier Science Ltd. All rights reserved.