H₂ Solubility in Pd/Cr₂O₃ Composites Prepared by Internal Oxidation of Pd−Cr Alloys: Equilibrium Pressure-Composition-Temperature Data

The solution of hydrogen and hydride formation in Pd/Cr 2 O 3 composites has been investigated. Internal oxidation of Pd−Cr alloys is employed to prepare the composites consisting of nanosized Cr 2 O 3 precipitates within Pd matrices. The dissolved H segregates to the internal Pd/Cr 2 O 3 interfaces. Plots of p H 2 1/2 versus H content for internally oxidized Pd−Cr alloys exhibit small positive intercepts along the H/Pd axis which can be attributed to trapping of H by Pd/Cr 2 O 3 internal interfaces. The amount of trapping is found to be directly proportional to the atom fraction Cr in the alloys after internal oxidation at the same temperature. In addition to the enhanced solubility noted from these intercepts, H 2 solubilities in the dilute phase of these internally oxidized alloys are larger than in pure Pd or in other internally oxidized Pd-rich alloys and these solubilities also increase with atom fraction Cr, X Cr . In contrast with internally oxidized Pd−Al alloys studied earlier, internally oxidized Pd−Cr alloys with X Cr ≥ 0.02 have an initial plateau p H 2 lower than those of Pd−H. The H 2 isotherms for internally oxidized alloys with X Cr ≥ 0.05 exhibit gradual phase transitions to the two phase coexistence region rather than an abrupt one as for annealed Pd.