Tuesday, 3 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
This study investigates the hydrogen adsorption properties of activated carbon (AC) doped with nickel nanoparticles, and the effects of surface oxygen functional groups in AC on hydrogen uptake at room temperature. The oxidized AC (AC_OX) sample was prepared by mixing AC in a mixture of H2SO4, deionized water and HNO3 solution. By using an electroless plating process, nickel was deposited into oxidized AC (AC_OX) and denoted as Ni/ AC_OX. The oxidized activated carbon was characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectra to obtain the functional groups and structural information, respectively. After acid oxidation treatment, the integrated intensity ID/IG for the AC_OX sample is higher than that for the AC sample, indicating that the presence of defects on the former is more obvious than that on the latter. The defects facilitate the adsorption of gases and serve as reactive sites for chemical reactions, and thus surface defects are a key to the nucleation, growth, and stability of metal clusters on the support. The particle size distribution and morphology of nickel were also characterized by SEM and TEM. The SEM image of Ni/AC_OX is apparent that the deposited Ni catalyst has a narrow distribution of particle sizes between 10-20 nm in diameter, nickel content of approximately 8~10 wt. %. The specific surface area (SSA) of samples was determined at 77 K with an analyzer Quantachrome Autosorb-1 using N2 as the adsorbent. The BET surface areas of the AC, AC_OX and Ni/AC_OX samples were determined to be 1100, 870 and 340 m2/g, respectively. In addition, the total pore volumes for samples AC, AC_OX and Ni/AC_OX were 0.7, 0.55 and 0.22cc/g. The acidic oxidation treatment has very little impact on the texture of pristine AC. The decrease in SSA and pore volume in the Ni/AC_OX sample was attributed to the filling and blockage of pores of Ni by an electroless plating process. The pore size distribution patterns of AC, AC_OX and Ni/AC_OX are concentrated below 2 nm, with clear peaks at 0.7 and 1.4 nm. Hydrogen uptake measurements of AC, AC_OX and Ni/ AC_OX were performed using a commercial Sievert’s apparatus. The Raman and FTIR spectra demonstrated that the oxidized AC exhibited a slightly defective surface and oxygen functional groups. The hydrogen uptake of AC, AC_OX and Ni/AC_OX is 0.35, 0.21 and 0.58 wt.%, respectively. The RT hydrogen uptake of catalyst-free AC supports is proportional to the specific surface area and micro-pore volume The acidic oxidation treatment of AC sometimes causes a reduced pore volume and specific surface area, resulting in decreased hydrogen adsorption. It has been reported that oxygen functional groups on carbon can help hydrogen adsorption through the increased hydrogen binding energies. We thus speculated that Ni catalysts supported on oxidized AC could compensate for the low specific surface area, and thus achieve a hydrogen uptake comparable with that of pristine AC. Compared to the RT hydrogen uptake for the pristine AC sample of 0.35 wt%, the amount of hydrogen uptake for Ni/AC_OX is enhanced via spillover by a factor of 1.66. The findings further suggest that surface functionalization is essential for effective doping of Ni catalysts onto AC supports for the spillover process.