Nature of hydrogen atom trapped inside palladium lattice

Abstract

Colloid of palladium nanoparticles has been prepared by the Solvated Metal Atom Dispersion (SMAD) method. Reaction of Pd(0) nanopowder obtained upon precipitation from the colloid, with ammonia–borane (H₃N·BH₃, AB) in aqueous solutions at room temperature results in the generation of active hydrogen atoms. The active hydrogen atoms either combine with one another resulting in H₂ evolution or diffuse into the Pd lattice to afford PdH_x. Diffusion of hydrogen atoms leads to an expansion of the Pd lattice. The diffused hydrogen atoms are distributed uniformly over the entire particle. These features were established using powder XRD and electron microscopy studies. The ₁H NMR spectral studies of PdH before and after desorption of H₂ revealed that the hydrogen atoms trapped inside Pd lattice are hydridic in nature. Desorption of hydrogen from PdH_x did not result in complete reversibility suggesting that some hydrogen atoms are strongly trapped inside the Pd lattice.