Hydrogen Storage
by Prof. A.D. Lueking

The Hydrogen Fuel Initiative announced by President Bush in his January 2003 State of the Union Address advocates the development of a hydrogen fuel economy for improved energy efficiency and the diversification of the nation’s energy sources. Hydrogen is an energy carrier, similar to gasoline: both are mobile sources of chemical energy derived from other primary energy sources. Compared to gasoline, hydrogen has higher energy conversion efficiency, reduced emissions, and diversifies energy supply as it can be produced chemically from fossil fuels, from decomposition of biomass, or through electrolysis of water powered by renewable energy. Development of a hydrogen economy will require advances in methods by which to produce, store, transport, and distribute hydrogen in an economically viable manner.

Hydrogen storage goals are based on practical considerations to enable a 300-mile vehicle range [1]. Compressed and cryogenic hydrogen storage methods do not meet storage targets and are further limited by safety concerns. No existing solid-state storage material meets 2010 storage goals, and incremental advances in existing materials are not likely to meet these targets.

Metal hydrides capable of meeting gravimetric targets (i.e. MgH₂) are limited by slow desorption rates and high desorption temperatures. Alloying metal and chemical hydrides with transition metals increases dehydrogenation rates and lowers desorption temperatures, but does so at the expense of overall gravimetric storage. Variations in synthesis conditions, experimental artifacts, and contamination have led to disputed hydrogen storage reports in carbon-based adsorbents. However, residual metal content may be used advantageously to activate a previously inert surface; carbon nanotubes are especially amendable to this activation due to a high-surface area, delocalized electrons, and tunable physical properties. A synergistic effect has been observed that leads to an increased overall uptake for the composite material compared to its component materials.

On-going Activities.  The Lueking research group is working to probe the underlying chemistry and physics of carbon-metal-hydrogen interactions, or hydrogen spillover, in catalyzed carbon composites to facilitate optimization of hydrogen uptake using fundamental relations rather than an Edisonian approach.