Aluminum may soon be a new application for hydrogen storage for fuel cells.
Lightweight interstitial hydrides — compounds in which hydrogen atoms occupy the interstices (spaces) between metal atoms – could be a safe and efficient means for storing hydrogen for fuel cell vehicles.
Hydrides using magnesium, sodium and boron are out there, but so far, none appear practical as a hydrogen repository. An aluminum-based alloy hydride offers a more viable candidate because it has the desired traits of light weight, no toxicity to plants and animals, and absence of volatile gas products except for hydrogen. Until now, however, researchers only put together complex aluminum hydrides — unsuitable for use as a hydrogen storage system.
A joint research group with members from the Japan Atomic Energy Agency (Hyogo, Japan) and Tohoku University (Sendai, Japan) said it achieved the long-sought goal of a simple-structured, aluminum-based interstitial alloy. They were able to synthesize their compound, Al2CuHx, by hydrogenating Al2Cu at an extreme pressure of 10 gigapascals (1.5 million pounds per square inch) and a high temperature of 800 degrees Celsius (1,500 degrees Fahrenheit).
The researchers characterized the conditions of the hydrogenation reaction using in-situ synchrotron radiation X-ray diffraction measurement, while the crystal and electron structures of the compound formed ended up studied with powder X-ray diffraction measurement and first-principle calculations, respectively. Together, these examinations confirmed the first-ever formation of an interstitial hydride of an aluminum-based alloy.
“Although its synthesis requires very extreme conditions and its hydrogen content is low, our new compound showed that an aluminum-based alloy hydride is achievable,” said Hiroyuki Saitoh, lead author of a paper on the subject.
“Based on what we’ve learned from this first step, we plan to synthesize similar materials at more moderate conditions — products that hopefully will prove to be very effective at storing hydrogen.”