Strategies toward Enhanced Low-Pressure Volumetric Hydrogen Storage in Nanoporous Cryoadsorbents Afsana Ahmed, †,‡ Aaron W. Thornton,* ,‡ Kristina Konstas, ‡ Sridhar Kumar Kannam, † Ravichandar Babarao, ‡ B. D. Todd, † Anita J. Hill, § and Matthew R. Hill ‡ † Mathematics Discipline, Faculty of Engineering and Industrial Science and Centre for Molecular Simulation, Swinburne University of Technology, Melbourne, Victoria 3122, Australia ‡ Materials Science and Engineering and § Process Science and Engineering, CSIRO, Private Bag 33, Clayton South MDC, Victoria 3169, Australia * S Supporting Information ABSTRACT: The volumetric hydrogen capacity remains one of the most challenging criteria for on-board hydrogen storage system requirements. Here a new concept for hydrogen storage of porous aromatic frameworks (PAFs) impregnated with lithium-decorated fullerenes (Li 6 C 60 ) is described. The loading of Li 6 C 60 and the effect on the adsorption of hydrogen (H 2 ) has been investigated by molecular simulation. It is shown that the incorporation of Li 6 C 60 can enhance the volumetric capacity of H 2 from 12 to 44 g L -1 , a 260% increase at 10 bar and 77 K. The impregnation of Li 6 C 60 increases the heat of adsorption and surface area at the cost of the available pore volume. However, the increase in adsorbed hydrogen outweighs any pore volume loss under optimized Li 6 C 60 loading and operating conditions. In addition, the H 2 volumetric uptake is shown to correlate with the volumetric surface area at all pressures whereas the H 2 gravimetric uptake correlates with the heat of adsorption at low pressures, surface area at moderate pressures, and pore volume at high pressures. I. INTRODUCTION During the past decade, a significant amount of research has been performed on nanoporous materials, which not only possess high surface areas but also reversibly adsorb or desorb hydrogen under pressure-swing and temperature-swing con- ditions. 1-9 They possess intrinsically high surface areas and internal volumes, and these factors are known to enhance gas storage at cryogenic temperatures. 10 A recent report from the U.S. Department of Energy (DoE) suggests that cryosorbents 11 are promising on-board hydrogen storage systems, although the capacity targets are yet to be met. 11 Even though cryoconditions are not within the DoE requirements, there is considerable research in cryocompressed systems to meet the DoE capacity targets. 12-16 Hydrogen has always been considered to be a medium for clean energy because of its universal abundance and lack of carbon emissions during use. The production of hydrogen remains a challenge, although technologies such as the steam reformation of coal/oil/gas, 17 fermentation of organic waste, 18 photodecomposition of water or organic compounds using bacteria, 19 and photocatalytic water splitting 20 are viable options. To make the hydrogen- driven fuel cell vehicle viable, efficient, safe, and economically sound hydrogen storage systems are needed. 21 A few years ago, the U.S. DoE set a number of targets for hydrogen storage systems including capacity requirements: 4.5 wt % or 28 g L -1 by the year 2010 and 5.5 wt % or 40 g L -1 by the year 2017. 11 Physical adsorbents have achieved high hydrogen capacities but usually at cryogenic temperatures. Fortunately, engineering work has pushed the viability of cryocompressed hydrogen into the realm of industrial feasibility. 11-16 Designing adsorbent materials by tailoring the heat of adsorption, surface area, and pore volume is an effective strategy for enhancing the hydrogen capacity. Some of the leading candidates include metal -organic frameworks (MOFs) 22 -27 and covalent organic frameworks (3D COFs) 28-32 with surface areas of up to 7000 m 2 g -1 (Farha et al. 33 ) and 5172 m 2 g -1 (Babarao et al. 34 ), respectively. The most important drawback of most of the MOFs and COFs is their low chemical stability. The development of porous aromatic framework (PAF) materials provides a combination of ultrahigh surface area and high physicochemical stability. PAFs were recently reported as a new family of ultraporous materials with BET surface areas above 5000 m 2 g -1 . 35,36 Consisting of fused diamandoid tetrahedra with pore size distributions centered around 12 Å, these carbonaceous materials have been shown to deliver hydrogen storage capacities of 7 wt % at 48 bar and 77 K. These values, although when compared to most materials are exceptional, are Received: October 7, 2013 Revised: November 26, 2013 Published: November 27, 2013 Article pubs.acs.org/Langmuir © 2013 American Chemical Society 15689 dx.doi.org/10.1021/la403864u | Langmuir 2013, 29, 15689-15697