Jun 10, 2009
Melt infiltration aids hydrogen delivery
Efficient, compact and safe hydrogen storage is essential to realize the hydrogen economy. Especially given that the on-board storage of hydrogen in vehicles poses strict requirements in terms of weight and hydrogen-release properties. Lightweight metal hydrides hold great potential for reversible solid-state hydrogen storage, but no material system has yet been identified that simultaneously meets all of the requirements.
Several lightweight metal hydrides such as MgH2 and NaAlH4 have high gravimetric hydrogen contents. However, they suffer from relatively slow kinetics and high hydrogen-release temperatures. One strategy for improving the hydrogen-release properties of these materials is to reduce the particle size and add small amounts of highly dispersed catalysts.
Testing the idea
Researchers at the Debye Institute for Nanomaterials Science at Utrecht University have pioneered a melt infiltration method to prepare carbon-supported light metal hydride nanomaterials such as nanosized MgH2. In a paper published recently in Nanotechnology, the group describes the preparation method and reveals the subsequent hydrogen sorption properties of its carbon supported Mg(Ni)Hx nanocrystallites. The materials were prepared by magnesium melt infiltration of nanoporous carbon-containing nickel nanoparticles, followed by cooling and hydrogenation.
Bulk MgH2 contains 7.7wt% of hydrogen, although the gas is released typically only at 400–450 °C. From the bulk phase diagram full phase segregation into MgH2 and Mg2NiH4 would be expected, but the supported nanomaterials showed no hydrogen release in this temperature range.
Even for high MgH2 loadings (50wt%) and a relatively low nickel content (corresponding to Mg0.95Ni0.05 atomic composition) hydrogen-release temperatures were effectively lowered by 100–200 °C compared with bulk MgH2. The favorable hydrogen desorption properties could be attributed mainly to the excellent kinetics brought about by the efficient mixing of magnesium, nickel and carbon on the nanoscale.
The results illustrate the potential of this preparation technique for designing nanoscale mixtures of metals and provide access to studies on the thermodynamic and kinetic hydrogen sorption properties of nanocrystalline mixed light-metal alloy (hydrides).
About the author
The research was carried out at Utrecht University, the Netherlands, in the group of Inorganic Chemistry and Catalysis (headed by Prof. Krijn de Jong) at the Debye Institute of Nanomaterials Science. Within this group the hydrogen team (led by Dr Petra de Jongh) investigates the possibilities of nanostructured materials for efficient on-board hydrogen storage. Postdoctoral fellow Philipp Adelhelm and MSc student René Bogerd are members of this team, while Hans Meeldijk is an electron microscopy expert in the Electron Microscopy group at the Department of Biology of Utrecht University.