Better Hydrogen Storage
Nanosponge works on molecular level />
CONTEXT: Hydrogen may be the fuel of the future, but major hurdles prevent it from being as versatile as oil. Storing hydrogen is one problem, particularly for cars and mobile devices; pressurized hydrogen gas must be stored in thick-walled tanks and so requires far more space than its energy equivalent in gasoline. Alternative-energy researchers have sought materials that could act as sponges, soaking the hydrogen in and holding it until it is needed, but no material so far has had the necessary hydrogen capacity at convenient temperatures and pressures.
Researchers from the University of Newcastle upon Tyne and the University of Liverpool have shaken up the hydrogen research community by discovering a new class of materials that addresses the problem at the molecular level.
METHODS AND RESULTS: The materials made by Xuebo Zhao and colleagues are composed of long carbon chains linked by metal atoms. When they are crystallized, these molecules frame cavities less than a nanometer across, connected by “windows” that are even smaller than a hydrogen molecule. While the cavities are being filled, hydrogen can wriggle through these windows because the carbon chains are flexible.
But once the cavities fill, the chains lose their room to flex, forcing the windows closed. As a result, the material can be loaded with hydrogen gas at high pressure, but does not release the gas when pressures drop to normal, essentially forming a molecule-sized pressure seal.
WHY IT MATTERS: Fuel cells running on hydrogen could be good for much more than cars; they could work in portable electronic devices such as laptops, handheld computers, and cell phones. While the materials made by Zhao and colleagues do not hold enough hydrogen for most commercial applications and only work far below room temperature, they open up an entirely new approach to hydrogen storage. With some amount of refinement, this nanoscale sponge could become a key part of a hydrogen economy.
SOURCE: Zhao, X., et al. 2004. Hysteretic adsorption and desorption of hydrogen by nanoporous metal-organic frameworks. Science 306:1012-1015.