Pd-Cu-M (M = Y, Ti, Zr, V, Nb, and Ni) Alloys for the Hydrogen Separation Membrane.

Self-supported fcc Pd-Cu-M (M = Y, Ti, Zr, V, Nb, and Ni) alloys were studied as potential hydrogen purification membranes. The effects of small additions (1-2.6 at. %) of these elements on the structure, hydrogen solubility, diffusivity, and permeability were examined. Structural analyses by X-ray diffraction (XRD) showed the fcc phase for all alloys with induced textures from cold rolling. Heat treatment at 650 °C for 96 h led to the reorientation in all alloys except the Pd-Cu-Zr alloy, exhibiting the possibility to enhance the structural stability by Zr addition. Hydrogen solubility was almost doubled in the ternary alloys containing Y and Zr compared to Pd65.1Cu34.9 alloy at 300 °C. It was noted that hydrogen diffusivity is decreased upon additions of these elements compared to the Pd65.1Cu34.9 alloy, with the Pd-Cu-Zr alloy showing the lowest hydrogen diffusivity. However, the comparable hydrogen permeability of the Pd-Cu-Zr alloy with the corresponding binary alloy, as well as its highest hydrogen permeability among the studied ternary alloys at temperatures higher than 300 °C, suggested that hydrogen permeation of these alloys within the fcc phase is mainly dominated by hydrogen solubility. Hydrogen flux variations of all ternary alloys were studied and compared with the Pd65.1Cu34.9 alloy under 1000 ppm of H2S + H2 feed gas. Pd-Cu-Zr alloy showed superior resistance to the sulfur poisoning probably due to the less favorable H2S-surface interaction and more importantly slower rate of bulk sulfidation as a result of improved structural stability upon Zr addition. Therefore, Pd-Cu-Zr alloys may offer new potential hydrogen purification membranes with improved chemical stability and hydrogen permeation compared to the binary fcc Pd-Cu alloys.

Destabilisation of the Li-N-H hydrogen storage system with elemental Si.

A significant improvement in the dehydrogenation kinetics of the (LiNH(2) + LiH) system was obtained upon doping with elemental Si. Whilst, complete dehydrogenation of the (LiNH(2) + LiH) system requires more than 2 h, the time required for full dehydrogenation was reduced to less than 30 min by doping with elemental Si. It is observed that Si thermodynamically destabilises the system through the formation of novel intermediate phases resulting from the reaction of Si with both LiNH(2) and LiH. Such intermediate phases are also believed to enhance reaction kinetics by providing a path for accelerated dehydrogenation and the rapid release of hydrogen at the early stages of the reaction. It is believed that the dehydrogenation kinetics of the (LiNH(2) + LiH) system, which is controlled by the diffusion of H(-) from LiH and H(+) from LiNH(2), becomes independent of diffusion upon Si addition due to an enhanced concentration gradient in reactive ionic species.