Modified Carbon Cryogel-Ammonia Borane Nanocomposites for Hydrogen Storage

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1042-S07-01

Modified Carbon Cryogel-Ammonia Borane Nanocomposites for Hydrogen Storage Saghar Sepehri, Betzaida Batalla Garcia, Qifeng Zhang, and Guozhong Cao Material Sience and Engineering, University of Washington, 302 Roberts Hall, Box 352120, Seattle, WA, 98195 ABSTRACT This paper reports the synthesis and characterization of coherent Boron/Nitrogen –doped –carbon cryogels- ammonia borane nanocomposites for hydrogen storage. Resorcinol formaldehyde derived doped carbon cryogels (CC) were obtained via chemical modification.CCammonia-borane nanocomposites were made by incorporation of ammonia borane (AB), in CCs. Nitrogen sorption analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy, are used to investigate the structure and morphology of the modified CCs. Differential scanning calorimetry is used to study the dehydrogenation of coherent doped-CC-AB nanocomposites. Modified CCs show higher mesoporosity, and more homogeneous porous structure compared to undoped CCs. Also, dehydrogenation kinetics of nanocomposites is enhanced as compared to neat AB. Possible nanoscale and catalytic effects of nanocomposites in improved dehydrogenation kinetics are discussed. INTRODUCTION Carbon cryogels (CCs) with desirable properties, including tunable mass densities, continuous porosities, and high surface area, have attracted a considerable attention for numerous applications [1- 6]. CCs can be made from organic hydrogels generated by the sol-gel polycondensation of organic monomers such as resorcinol (R) and formaldehyde (F) in aqueous solution in the presence of a polymerization catalyst [7]. The precursor hydrogels can be dried by different methods including supercritical drying or freeze drying. Aerogels are produced by drying the RF hydrogel by supercritical extraction with carbon dioxide, while cryogels are resulted via freeze-drying. Freeze-drying is an appealing alternative to the expensive supercritical drying while still producing similar porous structure [8]. Dried hydrogels are highly porous materials with a large surface area. Carbon aerogels (CAs) and CCs are produced by pyrolysis of hydrogels that provide a through-connected mesoporous network. Final porous structure of the CAs and CCs depend on the synthesis and processing conditions and can be tailored to obtain desired micro and mesoporosity [9]. By IUPAC classification regarding pore widths: micropores 50nm [10]. In addition to tailoring the pore structure, doping carbon gels can provide them with altered or novel properties that expand their applications. Incorporation of metals, nitrogen and boron species into carbon materials, including CAs and CCs, can modify their structure, conductivity, and catalytic activity [11,12]. Recently, CAs have been considered as a new candidate for hydrogen storage. CAs and CCs are light weight materials and therefore they can show good gravimetric hydrogen density when used as a support for hydrides. Also, optimization of pore and particle sizes in porous carbon structures can provide better heat tra

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