1H NMR study of hydrogen in palladium nanocrystals

We investigate the H-1 nuclear magnetic resonance (NMR) of hydrogen absorbed in a nanometer-sized (similar to 3 nm and similar to 8 nm) palladium crystalline powder. At room temperature and hydrogen pressures above 30 Torr, the NMB. spectra show double peaks. These manifest the existence of subsurface absorption sites and confirm that the susceptibility of palladium decreases abruptly in the grain-boundary region. We also measure the spin-lattice relaxation time T-1 and calculate the activation energies for hydrogen motions at the subsurface and the bulk sites. The activation energies are lower for smaller size particles. This is related to a nonlocal structural change in the nanometer-sized palladium crystals.