Abstract
This paper reports on differences in stability of Pd hydride phases in palladium particles with various degrees of contact with microporous carbon supports. A sample containing Pd embedded in activated carbon fiber (Pd-ACF; 2 wt% Pd) was compared with commercial Pd nanoparticles deposited on microporous activated carbon (Pd-catalyst, 3 wt% Pd) and with support-free nanocrystalline palladium (Pd-black). The morphology of materials was characterized by electron microscopy, and the phase transformations were analyzed over a large range of hydrogen partial pressures (0.003 - 10 bar) and at several temperatures using in-situ X-ray diffraction. The results were verified with volumetric hydrogen uptake measurements. Results indicate that higher degree of Pd-carbon contacts for Pd particles embedded in a microporous carbon matrix induce efficient �pumping� of hydrogen out of �-PdHx. It was also found that thermal cleaning of carbon surface groups prior to exposure to hydrogen further enhances the hydrogen pumping power of the microporous carbon support. In brief, this study highlights that the stability of �-PdHx phase supported on carbon depends on the degree of contact between Pd-carbon and the nature of the carbon surface.
