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.
Improving Your Memory
A faster, cheaper, smaller way to make computers remember
CONTEXT: Which takes longer, walking to and from the coffeepot, or starting up a computer? The answer, sadly, is often the latter. That’s because the most common computer memory technologies, DRAM and SRAM, are “volatile,” meaning they require power to retain data and must reload information when restarted. Other memory technologies, such as the flash RAM found in today’s digital cameras, cell phones, and PC cards, can hold data without power, but they read and write information too slowly to be used for computing purposes. Researchers at the University of California, Los Angeles, have recently designed a new form of fast, cheap memory, based on organic materials and nanoparticles, that seems to overcome many of these limitations.
METHODS AND RESULTS: A memory device is essentially a system that can switch between distinct states, like the “on” or “off” states of a transistor. Jianyong Ouyang and colleagues built a device from a thin film of material that switches between being more or less electrically conductive. They created a 50-nanometer-thick polymer film loaded with gold nanoparticles and an electron-rich carbon-based molecule, then sandwiched the film between two metal electrodes. When electrically grounded, the film can barely conduct a current. Apply enough voltage between the electrodes, however, and electrons move from carbon to gold, raising the conductivity through the sandwich by a factor of 10,000.
The transition occurs in less than 25 nanoseconds, the limit of what the team could detect; the states are stable even when the power is off and can be switched back and forth repeatedly. The polymer film is easy and cheap to make, and unlike silicon-based memory, these polymer-based devices could easily be built up in layers, enabling extremely high densities in a small volume.
WHY IT MATTERS: This research stands out from fierce competition because the cheap and simple methods reported yielded excellent performance, surpassing that of flash RAM and rivaling conventional computer memory.
But the streets of Silicon Valley are littered with the remains of engineers and investors who have tried and failed to break into the memory market. Ouyang and colleagues eventually must show that their memory device is reliable and can be manufactured on an industrial scale. Nonetheless, this new approach should be a contender in the battle for low-cost, high-density memory in digital cameras, cell phones, and personal computers.
SOURCE: Ouyang , J., et al. 2004. Programmable polymer thin film and non-volatile memory device. Nature Materials 3:918-922.
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