## New simple aluminum-based hydride for hydrogen storage

##### 11 November 2013

Japanese researchers report the development of a simple-structured, aluminum-based interstitial hydride for hydrogen storage in a paper in the AIP Publishing journal APL Materials. Their compound, Al2CuHx, was synthesized by hydrogenating Al2Cu at an extreme pressure of 10 gigapascals (1.5 million pounds per square inch) and a high temperature of 800 °C (1,500 °F).

Lightweight interstitial hydrides with high hydrogen content—such as Mg-based hydrides, alanates, borohydrides, and amino boranes—have been proposed as a safe and efficient means for storing hydrogen for fuel cell vehicles, but so far, none have proven 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. Although lightweight complex aluminum hydrides have been explored extensively, the researchers note, because of their thermodynamic properties and slow kinetics, those suited for practical applications have not yet been developed.

Interstitial aluminum-based alloy hydrides are expected to show properties different from those of the hydrides mentioned above. The hydrogenation and dehydrogenation reactions would simply proceed by a one-step process similar to conventional interstitial alloys such as LaNi5 showing LaNi5 + x/2H2 ⇔ LaNi5Hx suitable for practical application. In addition, the thermodynamic properties of interstitial aluminum-based alloy hydrides can be modified by partially or completely replacing their counterpart metal atoms; hence, the pressure–temperature conditions for hydrogen desorption and absorption reactions would become tunable. However, no interstitial aluminum-based alloy hydride has been synthesized so far, probably because aluminum tends to form Al–H covalent bonds.

In this letter, we demonstrate the formation of Al2CuHx (x ∼ 1) interstitial hydride. The crystal structure of the hydride proposed on the basis of X-ray diffraction experiments and first-principles calculations shows the characteristic alignment of hydrogen atoms. … The present results will help expanding the variety of aluminum-based alloy hydrides, helping in further developing practical hydrogen-storage materials.

—Saitoh et al.

The synthesis using high-temperature and high-pressure hydrogen atmosphere to form the alloy hydride twists the Al 8 Cu square antiprisms in Al 2 Cu around the c axis of a tetragonal unit cell.The twist enlarges the interstitial spaces for accommodating hydrogen atoms which align linearly parallel to the c axis in Al2CuHx.

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 were 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. 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.

Resources

• Hiroyuki Saitoh, Shigeyuki Takagi, Naruki Endo, Akihiko Machida, Katsutoshi Aoki, Shin-ichi Orimo and Yoshinori Katayama (2013) “Synthesis and formation process of Al2CuHx: A new class of interstitial aluminum-based alloy hydride,” APL Mat. 1, 032113 doi: 10.1063/1.4821632

Storing hydrogen more efficiently is to practical FCEVs what future more efficient batteries are to practical BEVs.

Future advancement in both technologies will make affordable FCEVs and BEVs practical and common place within 10 years or so?

ach technology may have its own niche markets.

@ HarveyD . With what you said and with all the future improvements that we find here in CCG the resale value of my actual car is shrinking each days at a rapid pace. Very soon peoples will buy better cars but i won't have the money to buy a new car. My only hope is that i can wait to 2025 approx to change my actual car and buy a used chevrolet volt at a good price so i will be able to get an electric car. Im doing researchs here about how to get out of gasoline operation. Maybe if hydrogen and bev become mainstream along with natural gas for trucking and if they find new biofuels to replace conventionnal crude petroleum fuels then maybe gas price will shrink and i will buy or keep my actual dodge neon till the end of time because real progress put in real commercialisation is done at a very low pace.

I gave up waiting for an extended range affordable EV and I bought a new Camry 2013 Hybrid and gave my very good old Camry to somebody (in the family) who needed a reliable old car.

I'm still in the market for a new EV but doubt that the electrified car we need will be around before 2020. By that time our (140) interior garages may be equipped with 220 VAC charging facilities.

By the way, after 4000+ Km we average 6.0 l/100 Km and that's very close to Toyota's claim. Our old Camry did closer to 10 l/100 Km. After 200,000 + Km, it could still do about 8.8 on highways but 12.5+ in town/city driving.

"Their compound, Al2CuHx, was synthesized by hydrogenating Al2Cu at an extreme pressure of 10 gigapascals (1.5 million pounds per square inch) and a high temperature of 800 °C (1,500 °F)."

This does not sound very economical.

If this is mass produced it could help to reduce the current huge aluminium surpluses and raise the price from a low $0.80/lb. to a more reasonable$1.20+/lb.

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