Comparative study on the influence of temperature, electrode potential and alloy bulk composition on hydrogen electrosorption into Pd-Pt and Pd-Au alloys

Hydrogen electrosorption into Pd-rich (>70% at. Pd in the bulk) Pd-Pt and Pd-Au alloys has been studied in acidic solutions (0.5 M H2SO4) using cyclic voltammetry and chronoamperometry. The influence of temperature (in the range between 283 and 328 K), electrode potential and alloy bulk composition on hydrogen electrosorption properties is presented. It has been found that with increasing temperature the maximum amount of absorbed hydrogen decreases and the potential of absorbed hydrogen oxidation peak and the potential of the alpha-beta phase transition are shifted negatively. Pd alloying with Pt or Au results in lower potential of absorbed hydrogen oxidation peak and lower maximum amount of absorbed hydrogen. The region of the alpha-beta phase transition for Pd-Pt alloys is placed at lower potentials as compared to pure Pd indicating lower thermodynamic stability of the beta-phase. In the case of Pd-Au alloys the phase transition region is placed at higher potentials indicating higher thermodynamic stability of the beta-phase. The values of time needed for electrode saturation with hydrogen and its removal decrease with increasing temperature and increasing bulk content of the alloying metals. The results have confirmed earlier suggestions that in the presence of both alpha- and beta-phases of absorbed hydrogen the slow process of the phase transition controls the rate of the overall electrosorption process in thin Pd-based electrodes. The amounts of electrosorbed hydrogen for alpha- and beta-phase boundaries, i.e. alpha(max) and beta(min), have been determined from the integration of the initial parts of current-time responses in hydrogen absorption and desorption processes. (C) 2010 Elsevier B.V. All rights reserved.