Electrolytic loading of hydrogen in Zr65(Pd80Rh20)35 and Zr65Pd35 alloys prepared by mechanical grinding and in their oxidised derivatives

Zr65(Pd80Rh20)35 and Zr65Pd35 alloys were prepared by mechanical grinding of stoichiometric amounts of either ZrH2 and Pd80Rh20 or ZrH2 and Pd. Following a suggestion in the literature, these alloys were converted by thermal oxidation in air into the corresponding ZrO2(Pd80Rh20) and ZrO2Pd compounds, which are probably composed of Pd80Rh20 and Pd nanostructures embedded in ZrO2. The aim of our work thereafter was to investigate hydrogen storage in these nanostructures. Both the alloys and their oxidation derivatives were thus loaded with hydrogen by cathodic reduction at 25°C in 6 M KOH, and loaded hydrogen was then determined by anodic extraction. On comparing the hydriding extent of the alloys with that of the corresponding oxidation derivatives, the metal clusters which formed after thermal oxidation are probably much larger in PdRh than in Pd. The former exhibits the high decomposition pressure typical of massive Pd80Rh20 hydride, and the maximum [H]/[Pd0.8Rh0.2] atom ratio is » 0.82. Conversely, the amount of hydrogen extracted from reduced ZrO2Pd samples prepared in optimal conditions fits [H]/[Pd] atom ratios between 1 and 2. The shape of the electrochemical hydrogen desorption isotherms indicates that the hydrogen in excess of the b–Pd hydride phase is probably stored in a new, very stable form.