Clean Technology 2009

Portable Hydrogen Generation using Carbon Cryogel-Ammonia Borane Nanocomposites

S. Sepehri, B. Batalla Garcia, K. Park, G. Cao, A.H. Brothers
Mainstream Engineering Corporation, US

Keywords: hydrogen, hydrogen storage materials, ammonia borane, fuel cell, nanocomposites


Among chemical hydride storage materials, ammonia borane (AB) shows great promise due to its high hydrogen content of 20 wt.% and low dehydrogenation temperature of ca. 105ºC. We have used carbon cryogels, porous carbon materials with controllable density, fully-interconnected nanoscale porosity, and high surface area, as scaffolds for AB. The resulting nanocomposites show up to 9 wt.% hydrogen release from AB at temperatures significantly lower (90ºC) than neat AB (105ºC), as well as suppressed formation of harmful borazine. These effects may be controlled via pore size, heating rate, and other parameters. The goal of this work was to better adapt CC-AB nanocomposites for use in portable hydrogen generators used with proton-exchange-membrane fuel cells (PEMFC) to power small electronics. Nanocomposite properties such as net hydrogen storage density, losses at low temperature, release kinetics at use temperature, and catalyst-poisoning byproducts were investigated and improved. The nanocomposite was then integrated into a test generator designed to provide ca. 10W of continuous fuel cell output by regulating nanocomposite hydrogen release, allowing the nanocomposite to be tested under realistic conditions for the first time. Incorporation of nanostructured hydrogen storage materials into such test generator systems helps identify problems and guide future development efforts.
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