Oct 29, 2010

Scientists work on sun-charged “heat battery

Sci­en­tists are en­vi­sion­ing a new type of re­charge­a­ble bat­tery that would store heat ab­sorbed from the sun in­stead of elec­tri­cal charge.

The idea is a step clos­er to real­ity, they say, with a new study re­veal­ing how a mol­e­cule called ful­va­lene diruthe­nium works to store and re­lease heat on de­mand.

A YouTube video from MIT scientists describes their research into a new type of re­charge­a­ble bat­tery that would store heat ab­sorbed from the sun.

Al­though the chem­i­cal, dis­cov­ered in 1996, is pro­hib­i­tively ex­pen­sive, re­search­ers pre­dict the new un­der­stand­ing should make it pos­si­ble to find si­m­i­lar, cheaper ma­te­ri­als. The find­ings are de­scribed in a pa­per in the Oct. 20 is­sue of the re­search jour­nal Ange­wandte Che­mie.

The mol­e­cule, ful­va­lene di­ru­the­nium, un­der­goes a struc­tur­al change when it ab­sorbs sun­light, put­ting it in­to a higher-en­er­gy state where it can re­main sta­ble in­def­i­nite­ly. This state is anal­o­gous to that of a rub­ber band that’s stretched and then put some­where where it stays stretched out for any de­sired length of time.

In the case of ful­va­lene di­ru­the­nium, the mol­e­cule can snap back in­to its orig­i­nal shape trig­gered by a small ad­di­tion of heat or a sub­stance called a cat­a­lyst. In the pro­cess, it re­leases the heat that was orig­i­nally ab­sorbed.

That’s a sim­pli­fied ver­sion of what hap­pen­s—but ac­tu­al­ly, the study re­vealed “there’s an in­ter­me­diate step that plays a ma­jor role” in the pro­cess, said Jef­frey Gross­man of the Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy, who led the re­search. In this mid­dle step, the mol­e­cule forms a semi-sta­ble con­figura­t­ion part­way be­tween the two pre­vi­ously known states. “That was un­ex­pect­ed,” he said, but it helps ex­plain why the mol­e­cule is so sta­ble, why the pro­cess is easily re­vers­i­ble and al­so why sub­sti­tut­ing oth­er el­e­ments for ru­the­ni­um has­n’t worked yet.

In ef­fect, ex­plained Gross­man, this pro­cess makes it pos­si­ble to pro­duce a “re­charge­a­ble heat bat­ter­y” that can re­peat­edly store and re­lease heat from sun­light or oth­er sources. In prin­ci­ple, Gross­man said, a fu­el made from ful­va­lene di­ru­the­nium, when its stored heat is re­leased, “can get as hot as 200 de­grees C, plen­ty hot enough to heat your home, or even to run an en­gine to pro­duce elec­tricity.”

Com­pared to oth­er solar-en­er­gy ap­proaches, he said, “it takes many of the ad­van­tages of solar-thermal en­er­gy, but stores the heat in the form of a fu­el. It’s re­vers­i­ble, and it’s sta­ble over a long term. You can use it where you want, on de­mand. You could put the fu­el [out] in the sun, charge it up, then use the heat, and place the same fu­el back in the sun to recharge.”

Be­cause of its cost, this mol­e­cule “is the wrong ma­te­ri­al, but it shows it can be done,” he added.

The next step, he ex­plained, is to use a com­bina­t­ion of sim­ula­t­ion, think­ing, and databases of tens of mil­lions of known mol­e­cules to look for oth­er can­di­dates that have struc­tur­al si­m­i­lar­i­ties and might show the same be­hav­ior. “It’s my firm be­lief that as we un­der­stand what makes this ma­te­ri­al tick, we’ll find that there will be oth­er ma­te­ri­als” that will work the same way, Gross­man said.



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