Hydrogen storage using physisorption – materials demands

Abstract

Abstract.A survey is presented of the storage capacities of a large number of different adsorbents for hydrogen at 77 K and 1 bar. Results are evaluated to examine the feasibility and perspectives of transportable and reversible storage systems based on physisorption of hydrogen on adsorbents. It is concluded that microporous adsorbents, e.g. zeolites and activated carbons, display appreciable sorption capacities. Based on their micropore volume (∼ 1 ml/g) carbonbased sorbents display the largest adsorption, viz. 238 ml (STP)/g, at the prevailing conditions. Optimization of sorbent and adsorption conditions is expected to lead to adsorption of ∼ 560 ml (STP)/g, close to targets set for mobile applications. In the last two decades there has been an increasing interest in the development of (transportable) reversible systems for hydrogen storage with a high capacity, which is critical to the large-scale application of hydrogen fuel cells, in particular for mobile applications [1]. Up to now focus has mostly been on liquid-hydrogen and metal-hydride systems, which both have low energy efficiencies [2]. A higher energy efficiency is attainable with systems in which hydrogen is concentrated by physical adsorption above 70 K using a suitable adsorbent [3][4][5]. Such an absorbent should be safe, light and cheap and of course have a high adsorption capacity. In order to obtain a suitable driving range for automotive applications the United States Department of Energy (DOE) target has been set to 6.5 wt %, which equals 720 ml (STP)/g adsorbent . Schwarz and co-workers [6-8] studied the applicability of molecularly engineered activated carbons and came up with promising results. Much excitement has arisen on recent reports on the use of carbon nanofibers [9] and carbon nanotubes [10,11] In this paper we present a survey of the storage capacity for hydrogen at 77 K and 1 bar of a large number of different types of adsorbents -silicas, aluminas, zeolites, graphite, activated carbons and carbon nanofibers -in a wide range of specific surface areas and of different textures, in order to give further direction to our research on the development of a suitable storage system. PACS

Carbide-Derived Carbons: Effect of Pore Size on Hydrogen Uptake and Heat of Adsorption

“…Carbon-based materials have received considerable attention in the context of physisorption. [1] Sorption processes require porous materials with a large number of sorption sites per unit mass or volume of an adsorbent, in other words materials with high specific surface area (SSA) (either gravimetric or volumetric) accessible to the sorbate. Many carbon structures with high SSA are known: activated carbon, exfoliated graphite, fullerenes, carbon nanotubes (CNT), nanofibers, etc.…”

“…[2] Intuitively, hydrogen adsorption on carbons comprised of graphene sheets should depend linearly on SSA, and the concept has been generalized to CNT and to carbons lacking graphitic short-range order . [1,3,4] The amount of reversibly adsorbed hydrogen on nanostructured graphitic carbon at -196 o C correlates with SSA for a large number of materials ranging from nanotubes to activated carbon (Fig. 1).…”

Characterization of dusts and impurities from the interaction between the first wall materials and energetic laser beams

“…The micropore portion was reported to be responsible for hydrogen adsorption, not mesopores or macro pores. 4 The alumina sample has majority of mesopores with an average pore diameter of about 100 Å. It lacks the micropores to capture hydrogen molecules.…”

“…Recently natural mordenite was reported to have higher H 2 and D 2 uptakes than 5A zeolite at liquid nitrogen temperature. 3 The H 2 uptake correlates with micropore surface area but not meso pores in various materials, 4 in which an activated carbon sample with over 2,000 m 2 /g surface area adsorbed three times as much H 2 as the best Zeolite. Langmuir (mono layer adsorption) constants were found well correlated with molecular weight of H and D hydrogen isotopes over various zeolites and activated carbons.…”

Molecular-dynamics analysis of the diffusion of molecular hydrogen in all-silica sodalite

“…[1][2][3] Porous solids for which the largest pore window openings have aperture dimensions similar to the kinetic diameter of hydrogen are especially interesting for hydrogen storage by means of encapsulation, i.e., trapping small gas molecules inside zeolitic cavities by changing the effective pore window opening to these cavities. This controlled encapsulation principle has previously been demonstrated in zeolites with respect to varying temperature, 4 and by application of an external force 5 to the material.…”