Novel Organometallic Fullerene Complexes for Vehicular Hydrogen Storage
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1041-R02-06
Novel Organometallic Fullerene Complexes for Vehicular Hydrogen Storage Erin Whitney, Anne C. Dillon, Calvin Curtis, Chaiwat Engtrakul, Kevin O'Neill, Mark Davis, Lin Simpson, Kim Jones, Yufeng Zhao, Yong-Hyun Kim, Shengbai Zhang, and Philip Parilla National Renewable Energy Laboratory, Golden, CO, 80401 ABSTRACT Experimental wet chemical approaches have been demonstrated in the synthesis of a new chainlike (C60-Fe-C60-Fe)n complex. This structure has been proposed based on 13C solid-state nuclear magnetic resonance, electron paramagnetic resonance, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. Furthermore, this structure has been shown to have unique binding sites for dihydrogen molecules with the technique of temperature-programmed desorption. The new adsorption sites have binding energies that are stronger than that observed for hydrogen physisorbed on planar graphite, but significantly weaker than a chemical C-H bond. Volumetric measurements at 77 K and 2 bar show a hydrogen adsorption capacity of 0.5 wt%. Interestingly, the BET surface area is ~31 m2/g after degassing, which is approximately an order of magnitude less than expected given the measured experimental hydrogen capacity. Nitrogen and hydrogen isotherms performed at 75 K also show a marked selectivity for hydrogen over nitrogen for this complex, indicating hidden surface area for hydrogen adsorption. INTRODUCTION A hydrogen-based economy offers the pollution-free promise of using entirely renewable resources.1 For example, hydrogen can be generated through the electrolysis of water using electricity derived from wind power, photovoltaics, or thermo-chemical processing of biomass. Once produced, hydrogen can then be used in fuel cells that convert hydrogen and oxygen back into water and produce electricity in the process. Hydrogen can also be combusted in an engine to generate mechanical energy or even burned to produce heat. Regardless of the scenario, water is produced in a virtually pollution-free cycle.1 However, one of the biggest challenges facing a future hydrogen economy is that of onboard vehicular hydrogen storage. Hydrogen is a nonpolarizable gas, making reversible solid state hydrogen storage a difficult challenge. Furthermore, neither compression of H2 to 10,000 p.s.i. or liquid hydrogen will satisfy all of the United States Department of Energy’s 2015 targets for hydrogen storage of 9 wt% or 81 kg H2/m3.2,3 Thus, in recent years, research has focused on novel carbon-based nanostructured materials, among others, as candidates for vehicular storage.4,5 Carbon is promising because it is a light element and thus a step towards the goal of lightweight hydrogen storage for transportation. Also inherent in the goal of hydrogen storage are the issues of near-room temperature operation at reasonable pressures. For an adsorption system, these challenges dictate a moderate binding energy for managing the heat load during refueling. Furthermore, the entire process must be complet
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