Disentangling the self-diffusional dynamics of H2 adsorbed in micro- and mesoporous carbide-derived carbon by wide temporal range quasi-elastic neutron scattering

Understanding the processes guiding the confinement of adsorbed H-2 in different porous structures is vital for the development of adsorbents for effective cryo-adsorptive H-2 storage systems. Quasi-elastic neutron scattering (QENS) is applied over a wide range of timescales (0.2 ps - 150 ps) to determine different self-diffusion mechanisms of H-2 adsorbed in a carbide (synthesized from TiC via the sol-gel method) derived carbon (sol-gel TiC-CDC) adsorbent with hierarchical porous structure. The bulk and porous structure is characterized by gas adsorption, Raman spectroscopy, and wide-angle X-ray scattering methods. Sol-gel TiC-CDC belongs to a series of CDCs that have been previously characterized and where the self-diffusion of adsorbed H-2 has been investigated with QENS. Sol-gel TiC-CDC is very mesoporous, has relatively high stacking (2.76 graphenic layers per stack), and small interlayer spacing of graphenic sheets (3.43 angstrom) in comparison to other CDCs in the series, thus, being a well-ordered highly porous CDC. Restricted rotational self-diffusion of adsorbed H-2 is determined in ultramicropores (pore width, w, < 7 angstrom) and translationally self-diffusing H-2 adsorbed in multilayers across multiple timescales are determined in micro- and mesopores (7 angstrom< w < 500 angstrom). The microporous and graphenic structure of the CDC does not remarkably affect the self-diffusion of H-2 at high surface coverages. The simultaneous determination of adsorbed H-2 motions across different timescales allows to analyze the influence of micro- and mesopores under H-2 loading conditions, which are close to the ones used in technical applications and are vital for adsorbent optimization.