The kinetic enhancement of hydrogen cycling in NaAlH(4) by melt infusion into nanoporous carbon aerogel.
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 cm(3) g(-1) was filled with NaAlH4 to 94% capacity by melt infusion at 189 degrees C under 183 bar H(2) gas overpressure. Dehydrogenation to NaH + Al with reasonable kinetics was accomplished at 150 degrees C, well below the NaAlH4 melting temperature (183 degrees C), compared to hydrogen release above 230 degrees 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 approximately 160 degrees C and 100 bar H(2) to approximately 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.
Chemical and Environmental Sciences Laboratory, General Motors Research and Development Center, Warren, MI 48090-9055, USA.
Robert D
RD
Stephens
Adam F
AF
Gross
Sky L
SL
Van Atta
John J
JJ
Vajo
Frederick E
FE
Pinkerton
D000388:Air; D017607:Aluminum Compounds / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D005782:Gels / Q000737:chemistry; D006358:Hot Temperature; D006859:Hydrogen / Q000737:chemistry* / Q000302:isolation & purification*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D017670:Sodium Compounds / Q000737:chemistry*; D013499:Surface Properties
D017607:Aluminum Compounds; D005782:Gels; D046911:Macromolecular Substances; D017670:Sodium Compounds; C513667:sodium aluminum hydride; D006859:Hydrogen