Hydrogen electrosorption in Pd–Pt–Rh alloys

The process of hydrogen electrosorption in thin Pd–Pt–Rh alloys has been investigated mainly in acidic solution using cyclic voltammetry and chronoamperometry. The influence of electrode potential on the amount of electrosorbed hydrogen is presented. On the plot of H/M (hydrogen atoms/metal atoms) vs. potential the regions of pure α- and β-phase existence as well as the region of α–β phase transition can be distinguished. The maximum amount of absorbed hydrogen depends on the bulk composition being relatively high for Pd-rich alloys, although smaller than for pure Pd. The α–β transition is shifted to lower potentials in comparison with pure Pd. The process of phase transition seems to control the rate of hydrogen absorption and desorption into/from thin Pd-based electrodes. The hysteresis effect is observed in chronoamperometric absorption and desorption experiments. Potential cycling of Pd–Pt–Rh alloys through the oxygen region leads to significant changes in hydrogen absorption properties with the appearance of an additional bulk phase.