Researchers' Hydrogen Storage Solution Is No Feather-Brained Idea
By John O'Dell June 25, 2009
By John O'Dell, Senior Editor
It's pretty clear by now that one of the main obstacles to commercializing fuel-cell electric vehicles is the lack of a hydrogen fueling infrastructure.
A little more range from a tank of the hydrogen gas that fuel cells require to produce electricity also would be nice.
How to store the gas, which has an extremely low density, is one of the stumbling blocks, but researchers at the University of Delaware think they're on the way to developing a solution.
The secret is chicken feathers. Carbonized chicken feathers to be exact.
Seems the fluffy stuff is made of keratin, a protein that forms microscopic tubes riddled with pores when heated just right - tubes that are the optimum size for storing hydrogen gas.
A 20 gallon tank filled with hydrogen gas pumped in at the ambient temperature and pressure would hold enough of the stuff to propel a car about one mile, said Richard Wool, a chemical engineering professor at the university.
It's that low-density problem: at room temperature the volume of hydrogen containing the same amount of energy as a gallon of gasoline is 40 times that of the gas.
Most fuel-cell electric cars being tested today are getting the equivalent of 50 to 80 miles a gallon (a kilogram of hydrogen gas has the energy equivalent of a gallon of gasoline) but carry their fuel in pressured tanks to avoid having to tow around box-car sized external tanks of unpressurized fuel.
The industry uses two standard pressures - 350 bar, or 5,000 pounds per square inch; and 700 bar, or 10,000 psi.
But a tank small enough to fit in a car or SUV without taking up all of the cargo and passenger room can only hold about 4 kilograms of pressurized hydrogen.
And it takes loads of electricity to compress the gas. That's led to criticism that although hydrogen doesn't create CO2 or particulate pollutants in its direct use as a fuel, enough is created in the manufacturing and compression parts of the "well-to-wheel" life cycle to make hydrogen as dirty as gasoline.
The principal way to make the fuel green is to produce and compress it using electricity from renewable resources -- hydro- and solar power.
Substantially reducing the amount of energy used to compress it by lowering the compression is another way.
Engineers are experimenting with tank inserts - called sub-strata -that increase storage capacity in lightly pressurized tanks by boosting the surface area the gas can cling to.
But a 20-gallon tank stuffed with carbon nanotubes, one solution being studied, would cost about $5.5 million, Wool said in an interview. Those nanotubes don't come cheap.
The same tank stuffed with metal hydrides, another of the solutions being tested, could cost up to $30,000.
Enter chicken feathers, which Wool first started studying while working on problems associated with heat transfer in printed circuit boards.
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Mi\icroscope photos show untreated chicken feather fiber (top) and carbonized fiber riddled with tiny pores (bottom).
Stuffing that same 20-gallon hydrogen tank with carbonized chicken features would cost about $200, said researcher Erman Senoz, a doctoral candidate who is doing the chicken feather research with Wool.
Hmm. $200 or $5.5 million? It's a wonder hydrogen boosters aren't literally throwing money at Wool and Senoz .That 20 gallon tank still wouldn't get you very far - perhaps 80 miles - and the Department of energy has set a goal of a 300-mile minimum range vehicles that use hydrogen fuel.
Senoz figures that at the state of the art today it would take a 75 gallon tank stuffed with 300 kilograms of carbonized chicken feathers to hold 300 miles worth of hydrogen - about 4.5 kilograms of the gas. That means the feather material stores 1.5 percent of its weight.
The goal now, Senoz said,i s to get the storage ratio up to 6 percent, so that 300 miles figure out how to make the carbonized feathers even more porous so that it would take only 75 pounds to hold 4.5 kilos of hydrogen.
One plus, as he carbonizes piles of fluffy feathers in his lab, is that there are lots of them. The U.S. poultry industry needs to get rid of about 2 billion pounds of chicken feathers each year, he said.
Add turkey feathers - which he and Wool believe would work just as well - and the sky's the limit.
Wool said his team is working on other uses of carbonized feather fibers, including wind-resistant, waterproof lightweight roofing material, plastics - including car parts - and printed circuit boards.
"Getting rid of all the feathers the chicken industry produces each year is a problem itself," Wool said. "Maybe we can help."
One potential problem - and you'll understand if you've ever burned one - is that carbonizing chicken feathers creates a nasty odor.
The carbonizing process doesn't actually consume them in flames, rather Senoz (right) says he slowly heats the feathers to about 400-degrees Fahrenheit.
That shrinks them, strengthens the keratin and creates the micro-pores that increase the feathers' hydrogen storage capacity.
Meantime, Senoz labors on, hoping to be able to increase the feather-to-hydrogen storage ratio t that magic 6 percent before his doctoral program ends.
"I've been working on this for three years," he said. "I've got two more to go."
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