Author/Authors :
Stephens, Robert D General Motors Research and Development Center - Chemical and Environmental Sciences Laboratory, USA , Gross, Adam F HRL Laboratories, LLC, USA , Van Atta, Sky L HRL Laboratories, LLC, USA , Vajo, John J HRL Laboratories, LLC, USA , Pinkerton, Frederick E General Motors Research and Development Center - Materials and Processes Laboratory, USA
Abstract :
Enhanced kinetic performance and reversibility have been achieved with uncatalyzed NaAlH4 by incorporation into nanoporous carbon aerogel. Aerogel with a pore size distribution peaked at 13 nm and a pore volume of 0.8 cm3 g−1 was filled with NaAlH4 to 94% capacity by melt infusion at 189 °C under 183 bar H2 gas overpressure. Dehydrogenation to NaH + Al with reasonable kinetics was accomplished at 150 °C, well below the NaAlH4 melting temperature (183 °C), compared to hydrogen release above 230 °C for bulk uncatalyzed NaAlH4. Uncatalyzed bulk samples did not rehydrogenate under laboratory conditions, whereas NaAlH4 in a carbon aerogel host was readily rehydrogenated at ~160 °C and 100 bar H2 to ~85% of its initial capacity. Ball-milled NaAlH4 catalyzed with 4 mol% TiCl3 showed somewhat better kinetics compared to the infused aerogel; nevertheless, the large kinetic enhancement obtained by incorporation into carbon aerogel, even in the absence of a catalyst, demonstrates the substantial benefit of confining the NaAlH4 to nanoscale dimensions
