Kinetic limitations of the Mg(2)Si system for reversible hydrogen storage.
Despite the promising thermodynamics and storage capacities of many destabilized metal hydride hydrogen storage material systems, they are often kinetically limited from achieving practical and reversible behavior. Such is the case with the Mg2Si system. We investigated the kinetic mechanisms responsible for limiting the reversibility of the MgH2+Si system using thin films as a controlled research platform. We observed that the reaction MgH2 + 1/2Mg2Si + H2 is limited by the mass transport of Mg and Si into separate phases. Hydrogen readily diffuses through the Mg2Si material and nucleating MgH2 phase growth does not result in reaction completion. By depositing and characterizing multilayer films of Mg2Si and Mg with varying Mg2Si layer thicknesses, we conclude that the hydrogenation reaction consumes no more than 1 nm of Mg2Si, making this system impractical for reversible hydrogen storage.
Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA.
Stephen T
ST
Kelly
Sky L
SL
Van Atta
John J
JJ
Vajo
Gregory L
GL
Olson
B M
BM
Clemens
D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D006859:Hydrogen / Q000737:chemistry* / Q000302:isolation & purification*; D007700:Kinetics; D046911:Macromolecular Substances / Q000737:chemistry; D017633:Magnesium Silicates / Q000737:chemistry*; D008422:Materials Testing; D008956:Models, Chemical; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods; D010316:Particle Size; D013499:Surface Properties
D046911:Macromolecular Substances; D017633:Magnesium Silicates; C005013:Florisil; D006859:Hydrogen