Nanoconfinement of Mg6Pd particles in porous carbon: size effects on structural and hydrogenation properties

Abstract

Mg₆Pd nanoparticles as small as 4 nm have been synthesized inside the pores of porous carbon. They are formed by infiltration of Mg on previously formed Pd nanoparticles dispersed into carbon. Their crystalline structure, as evaluated by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS), differs from bulk Mg₆Pd since their particle size is close to the large crystal cell (∼2 nm) of this intermetallic compound. Indeed, as compared to bulk Mg₆Pd, the nanoparticles exhibit a simpler crystallographic arrangement and a higher atomic disorder. Both thermodynamic and kinetic H-sorption properties of Mg₆Pd nanoparticles differ from those of bulk Mg₆Pd. The H-kinetics of the Mg₆Pd nanoparticles are significantly faster than bulk and are stable for at least 10 sorption cycles. Thermodynamic destabilization of the hydrided state is also observed for Mg₆Pd nanoparticles. Changes in the hydrogenation properties are attributed to nanosizing as well as to the modified structure of the nanoparticles as compared to bulk Mg₆Pd.