Exceptional gravimetric and volumetric hydrogen storage for densified zeolite templated carbons with high mechanical stability

Significance Statement

As part of the drive towards the anticipated Hydrogen Economy, there are on-going intensive research efforts aimed at finding materials suitable for on-board hydrogen storage. Potentially useful storage materials are evaluated against gravimetric and volumetric uptake targets set at levels that would allow commercial and practical viability. However, the volumetric hydrogen uptake of porous materials is related to packing density, yet high surface area materials that are likely to have large gravimetric hydrogen uptake tend to have low density and therefore low volumetric uptake. To address this conundrum, researchers at the University of Nottingham lead by Professor Mokaya have successfully prepared high surface area zeolite templated carbons (ZTCs) that have excellent mechanical stability and which, when compacted undergo densification to a packing density of ca. 0.72 g cm−3 but crucially with hardly any loss in porosity; the surface area and pore volume are maintained at ca. 3000 m2 g−1 and 1.4 cm3 g−1). The retention of high porosity means that the densified ZTCs have impressive gravimetric hydrogen uptake, which remains high at 7.0 wt% at 20 bar and −196 °C. The densified ZTCs possess a combination of packing density, textural properties and hydrogen uptake hitherto not achieved in any porous material, and achieve exceptional and unprecedented volumetric hydrogen uptake of 50 g l−1 at 20 bar, and with higher values possible at pressures above 20 bar. A volumetric hydrogen storage capacity of 50 g l−1 at 20 bar is to date the highest value measured for any porous material.

Journal Reference: 

Eric Masika, Robert Mokaya.. Energy Environ. Sci., 2014,7, 427-434.

University of Nottingham, University Park, Nottingham NG7 2RD, UK.

Abstract

Zeolite templating successfully generates carbons with high surface area and pore volume ofca. 3300 m2 g−1 and 1.6 cm3 g−1, respectively. The templated carbons have an exceptional gravimetric hydrogen uptake of 7.3 wt% at 20 bar and −196 °C, and a projected maximum of ca.9.2 wt%. These hydrogen uptake values are the highest ever recorded for carbon materials. The zeolite templated carbons have excellent mechanical stability and when compacted at a load of 10 tons (740 MPa) undergo densification to a packing density of ca. 0.72 g cm−3 but with hardly any loss in porosity (surface area and pore volume are little changed at ca. 3000 m2 g−1 and 1.4 cm3 g−1) or gravimetric hydrogen uptake capacity, which remains high at 7.0 wt% at 20 bar and a projected maximum of ca. 8.8 wt%. The effects of densification (i.e., increased packing density) coupled with hardly any loss in porosity or hydrogen uptake means that the densified zeolite templated carbons achieve an exceptional and unprecedented volumetric hydrogen uptake of 50 g l−1 at −196 °C and 20 bar, and an estimated maximum of up to 63 g l−1 at higher pressure.

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