Abstract
Entrapping hydrogen molecules within the nanopores of solid adsorbents serves a unique alternative for on-board storing of hydrogen for transportation purposes. The key advantage of utilizing the physisorption process for hydrogen storage is the higher density values achieved with the adsorbed gas, compared to that of the compressed phase, translating into higher storage capacities at lower pressures. The necessary condition for superior adsorption is the presence of nanopores (< 7 Ȧ) which serves the most suitable environment of hydrogen adsorption. Despite numerous theoretical calculations or indirect experimental findings, there was no direct experimental result that measured the density of adsorbed hydrogen or compared the same with varying pore sizes. In the present study, we employed in-situ small angle neutron scattering (SANS) on adsorbed hydrogen over polyfurfuryl alcohol-derived activated carbon (PFAC), at room temperature and pressures up to ~200 bar, with an aim to provide for the first time direct experimental measurements of the effect of pore size and pressure on the density of the adsorbed hydrogen. SANS studies were carried out at the General-Purpose Small-Angle Neutron Scattering spectrometer, at the High Flux Isotope Reactor, at Oak Ridge National Laboratory. The measurements covered the Q-range from 0.01 to 0.8 Å-1, covering to pores in the range of 9 to 34 Å of the PFAC material. Initial studies suggested that the density of adsorbed hydrogen is higher than the bulk phase and increases with decrease in pore size. The calculated densification is higher at the lower pressure level.
