Hydrogen Adsorption on Ordered Mesoporous Carbons Doped with Pd, Pt, Ni, and Ru

Abstract

A soft-template synthesis and in situ doping were applied for dispersing transition metals palladium, platinum, nickel, and ruthenium on ordered mesoporous carbons as potential adsorbents for hydrogen storage. Three metal loadings (1, 5, and 10 wt %) on the carbons were obtained to study the effects of metal concentration on physical and chemical properties of the carbon adsorbents. The carbon adsorbents were characterized with TEM, XRD, Raman spectroscopy, and nitrogen adsorption apparatus for their physical and chemical properties, and evaluated for their hydrogen adsorption equilibria and kinetics at 298 K and hydrogen pressures up to 300 bar. The metal-doped carbons maintained the morphology of the pure ordered mesoporous carbon, although their specific surface area was significantly reduced. Hydrogen adsorption on the metal-doped carbons was enhanced by a factor 2.7−5.4 times over the pure carbon at hydrogen pressure of 800 Torr, and a factor of 1.38−3.69 at hydrogen pressure of 300 bar due to the spillover effect. Hydrogen adsorption on metal-doped carbons increases with metal loading for all metals except the Ni-doped carbons that showed a reverse trend. The 1 wt % Ni-doped carbon sample seems to be the best adsorbent for hydrogen adsorption; it adsorbs 0.13 wt % of hydrogen at 298 K and 800 Torr and 2.14 wt % of hydrogen at 298 K and 300 bar. Hydrogen adsorption/desorption hysteresis was observed in all metal-doped carbons, suggesting that part of the adsorbed hydrogen molecules/atoms did not spill over to the carbon surface and remained on the metal surface. All metal-doped carbons had equally faster adsorption kinetics at 298 K, and the metal loadings did not affect the hydrogen adsorption kinetics.