Hydrogen Storage in Novel Carbon-Based Nanostructured Materials
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0927-EE05-01
Hydrogen Storage in Novel Carbon-Based Nanostructured Materials Erin S. Whitney, Calvin J. Curtis, Chaiwat Engtrakul, Mark F. Davis, Tining Su, Philip A. Parilla, Lin J. Simpson, Jeffry L. Blackburn, Yufeng Zhao, Yong-Hyun Kim, Shengbai B. Zhang, Michael J. Heben, and Anne C. Dillon National Renewable Energy Laboratory, Golden, CO, 80401 *[email protected]
ABSTRACT Experimental wet chemical approaches to complex an iron atom with two C60 fullerenes, representing a new molecule, dubbed a “bucky dumbbell,” have been demonstrated. The structure of this molecule has been determined by 13C solid-state nuclear magnetic resonance (NMR) and electron paramagnetic spin resonance (EPR). Furthermore, this structure has been shown to have a unique binding site for dihydrogen molecules with the technique of temperature programmed desorption (TPD). The new adsorption site has a binding energy that is stronger than that observed for hydrogen physisorbed on planar graphite, but significantly weaker than a chemical C-H bond. These results indicate that further exploration of fullerene-based organometallic complexes could lead to a revolutionary discovery for onboard vehicular hydrogen storage. INTRODUCTION A hydrogen-based energy 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 that relies predominantly on renewable resources.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 the United States Department of Energy’s 2015 targets.2,3 Thus, in recent years, research has focused on novel carbon-based nanostructured materials as candidates for vehicular storage.4,5 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 completely reversible.4 Although not typically appreciated, the adsorption energies for hydrogen bound to carbon surfaces are, in general, quite weak or quite strong. Non-dissociative physisorption, due purely to van der Waals interactions, involves a binding energy of only ~4 kJ/mol, whereas a C-H chemical bond is typically close to 400 kJ/mol. The desired binding
energy range for reversible vehicul
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