Hydrogen induced structural modifications in size selected Pd-Carbon core-shell NPs: Effect of carbon shell thickness, size and pressure

Abstract

In the present work, the effect of size, pressure and carbon shell thickness on the hydrogen induced structural modifications in Pd–C core-shell nanoparticles (NPs) have been investigated by in-situ X-ray diffraction (XRD) technique. XRD study shows contraction in the lattice with decrease in size of the NPs. Hydrogen pressure dependent α-to β-phase transition is observed on increasing hydrogen pressure ( 1 × 10 − 4 to 100 mbar). Compared to pure Pd NPs, occurrence of α ↔ β phase transition at lower H pressure in Pd–C NPs indicates that Pd–H interaction is enhanced by the carbon shell. Further, increasing hydrogen partial pressure is accompanied by an increase in the lattice parameter along with the formation of β-phase. Change in lattice constant (Δa) at different rates indicates the relative dominance between adsorption and desorption at different pressures. The merits of Pd–C core shell NPs over bulk analogues make it a promising material for repeated hydrogen cycling applications. • Pd–H interaction in Pd–C core shell NPs critically depends upon NPs size, H pressure and C shell thickness. • Lattice contracts with the decrease in the size of NP. • α-to β-phase transition in Pd–C core-shell NPs depends upon pressure of hydrogen gas. • Pd–H interaction is enhanced due to the presence of carbon shell. • Lattice parameter increases with increase in hydrogen partial pressure.