Image courtesy of jurvetson via flickr
It is a mystery that has confounded scientists for the better part of the last decade - how to explain the superior hydrogen storage capabilities of metal hydrides? Just over a decade ago, in 1997, scientists added a small quantity of titanium to sodium alanate, a commonly used metal hydride, to evaluate its properties as a storage medium for hydrogen; metal hydrides are a type of alloy that absorb and store hydrogen within their structure - when subjected to heat, they can release the gas.
To their surprise, the titanium augmented sodium alanate's capabilities as a storage system - lowering the temperature at which hydrogen was released, making the process much more efficient, while allowing for easier refueling and storage of high-density hydrogen at more conventional pressures and temperatures.The result: a near-doubling of the stored gas' weight-percent when compared to other cheap materials. While a remarkable discovery, scientists had been unable to account for the particular findings; the mechanisms and chemistry that altered sodium alanate's properties were shrouded in mystery.
Fast forward to the present day; a team of scientists from UCLA's Henry Samueli School of Engineering and Applied Science may have just unraveled this long-standing question. Using a combination of molecular systems simulations and physics, Vidvuds Ozolins, the lead scientist on the project, and his colleagues scrutinized the structure of sodium alanate in its pure form - reckoning that they might find a clue within its atomic substructure and bond chemistry.
By studying the interactions between hydrogen and the material's structure at the temperatures of the gas' release, the scientists found that aluminum diffusion within the metal hydride's structure was the key step in the titanium's catalyzing reaction. In other words, the titanium helped accelerate processes in the hydride that were essential to extracting hydrogen at lower temperatures - an important realization that will help scientists gain a better understanding of other materials' properties as hydrogen storage systems (and lead to the discovery of better ones).
As has been noted in many quarters, including this one, hydrogen has proven to be an extremely unwieldy fuel source because of the difficulties in handling and storing it. Finding materials able to store the gas at high densities and in small, lightweight tanks has been a tremendous challenge; Ozolins and his colleagues hope their work will facilitate this breakthrough in the next few years.