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

Abstract Zr 65 (Pd 80 Rh 20 ) 35 and Zr 65 Pd 35 alloys were prepared by mechanical grinding of stoichiometric amounts of either ZrH 2 and Pd 80 Rh 20 or ZrH 2 and Pd. Following a suggestion in the literature, these alloys were converted by thermal oxidation in air into the corresponding ZrO 2 (Pd 80 Rh 20 ) and ZrO 2 Pd compounds, which are probably composed of Pd 80 Rh 20 and Pd nanostructures embedded in ZrO 2 . 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 Pd 80 Rh 20 hydride, and the maximum [H]/[Pd 0.8 Rh 0.2 ] atom ratio is ≈0.82. Conversely, the amount of hydrogen extracted from reduced ZrO 2 Pd 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 β-Pd hydride phase is probably stored in a new, very stable form.