Researchers Engineer Carbon Nanotube Scaffolds for Higher Density Hydrogen Storage
24 December 2008
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| The procedure expands the geometry of a SWCNT fiber (upper left) and then locks the expanded form into a stable shape with cross linkers (bottom). Click to enlarge. Credit: ACS |
Researchers at Rice University and the National Renewable Energy Laboratory (NREL) have engineered single-walled carbon nanotube (SWCNT) fibers to become a scaffold for the storage of hydrogen. The 3-D nanoengineered fibers physisorb twice as much hydrogen per unit surface area as do typical macroporous carbon materials.
These fiber-based systems can have high density, and combined with the outstanding thermal conductivity of carbon nanotubes, can point a way toward solving the volumetric and heat-transfer constraints that limit some other hydrogen-storage supports, the team writes in a paper published online 22 December in the Journal of the American Chemical Society.
Devising cost-effective and practical on-board hydrogen storage systems with sufficient storage density to support targeted driving ranges is an on-going problem for the development of hydrogen-fueled vehicles. The authors note that using high pressure storage tanks in consumer automobiles lessens their attractiveness. An alternative to large volume, weight and pressure tanks is reversibly binding hydrogen to a lightweight solid-phase support. This approach falls into two categories: covalent binding (chemisorption) of the dissociated hydrogen, usually as a metal hydride; and physical adsorption (physisorption) of the hydrogen molecule.
The use of physisorption rather than chemisorption of hydrogen atoms to a surface eliminates the need for high heating to desorb the hydrogen from the solid phase, thereby providing faster kinetics of release. This also provides high energy efficiency and essentially complete availability of all stored hydrogen at lower pressures, generally in the 1-100 atm range. In addition, it is desirable to have a storage medium that is stable upon cycling, that can provide good thermal conductivity to dissipate the heat of adsorption, and that has paths with minimal tortuosity for fast kinetics of uptake.
Although many solid-phase supports have been prepared, they are neither high density nor do they have high thermal conductivity for heat removal during the adsorption step. We show here the fabrication of chemically cross-linked 3-dimensional (3-D) frameworks of single-walled carbon nanotube (SWCNT) fibers. These fibers physisorb twice as much hydrogen, at low pressures, with respect to their surface areas, than typical macroporous carbon materials.
—Leonard et al. 2008
SWCNT fibers themselves do not have sufficient surface area for the storage of hydrogen because they are bundled together tightly. Swelling the fibers in oleum (20% free SO3, fuming sulfuric acid) causes them to swell. The expanded geometry can be locked in by inserting cross-links that are stable in oleum, resulting in an enlarged and stable structure even after removal of the solvent.
It is the interstitial spaces between nanotubes that could be tuned by the choice of intercalating acid and cross-linker, providing higher surface area for hydrogen adsorption and also a multifaced environment for the hydrogen to assume several points of physisorption contact.
—Leonard et al. 2008
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| Hydrogen uptake vs. specific surface area. The solid line is the fit and extrapolation obtained from samples (triangles). The dashed line correlates to the maximum surface excess values typically observed for macroporous carbons. The diamond is the data point obtained with the fluorinated fibers. Click to enlarge. Credit: ACS |
Extrapolating from their experimental results, the team concluded that their scaffolded SWCNT structure could support 3.7 wt % hydrogen uptake with a surface area of 1,000 m2/g and 7.4 wt % hydrogen uptake at 2,000 m2/g using only 2 bar of pressure.
The research team is working to synthesize the SWCNT fibers with better pore sizes for the storage of hydrogen, with the ultimate goal of developing a hydrogen vehicle fuel tank that works near ambient temperature and pressure. As part of this, they are investigating other methods than using oleum (which results in some challenges in removing trapped sulfuric acid) to achieve higher surface areas, and are also using the scaffolds as platforms for supporting metals to enhance the hydrogen uptake at ambient temperature.
Resources
Ashley D. Leonard, Jared L. Hudson, Hua Fan, Richard Booker, Lin J. Simpson, Kevin J. O’Neill, Philip A. Parilla, Michael J. Heben, Matteo Pasquali, Carter Kittrell, and James M. Tour (2008) Nanoengineered Carbon Scaffolds for Hydrogen Storage. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja806633p
It would cost the equivalent of 60 cents a gallon to charge and drive an electric car. The electricity to charge the car could come from solar or wind generated electricity. If all cars,had plug-in electric drive trains,the amount of electricity needed to replace gasoline is about equal to the estimated wind energy potential of the state of North Dakota.Why don't we use some of the billions in bail out money to bail us out of our dependence on foreign oil? This past year the high cost of fuel so seriously damaged our economy and society that the ripple effects will be felt for years to come. Why not invest in setting up some alternative energy projects on a national basis, create clean cheap electricity, create millions of badly needed new green collar jobs, and get out from under our dependence on foreign oil. What a win -win situation that would be. There is a great new book out called The Manhattan Project of 2009 Energy Independence NOW by Jeff Wilson. www.themanhattanprojectof2009.com
Posted by: Sherry | 25 December 2008 at 07:22 AM
Yes indeed now if only a battery existed that could be recharged in 5 minutes and provide a range between 200-300 miles for a mid size car with air conditioning in the Florida summer and heating in the Alaskan winter.
Posted by: Mannstein | 25 December 2008 at 05:53 PM
And wasnt the size of a buick and the cost of a house.
Posted by: wintermane2000 | 25 December 2008 at 06:56 PM
Mannstein:
That's what the ESSTor ESSU is (was) supposed to do.
It seems that more delays, efforts, time, $$ etc will be needed.
Sherry:
Your idea is excellent and there is no doubt that something even better than the ESStor ESSU could be mass produced with 10-20 years, if more research was funded and adequate automated mass prodcution facilities were built.
There is also no doubt that the world will progressively transition to electrified vehicles in the next two or three decades. It is just a metter of time, priority and resources.
Posted by: HarveyD | 26 December 2008 at 02:48 PM
We all agree that affordable, practical PHEVs and/or BEVs would be absolutely ideal.
[(Well, except those who think we should all walk.)]
What we can't agree on is how to get there.
It is not so simple as to pour money and priority on it.
The benefit-cost ratio of the Manhattan project was high, but it was a gamble and just because the results were good does not mean every other gamble is worth taking.
Unfortunately need, priority, front money and volume production are not enough to guarantee a practical product.
After more than 10 years, HEV market penetration has never exceeded 6% and is dropping.
A cash infusion may help – may not.
Posted by: ToppaTom | 27 December 2008 at 08:18 AM
Oh, and as for H2, as a replacement for electric power (for industry, ships, trucks or autos or etc), I am at a loss to understand it's momentum.
I hope H2 programs are not sucking any significant % of public/governmental funding.
If there is a future there, let private proponents fund it; at least until some real promise emerges.
The world economies seem less able than ever to support a costly transition to an H2 economy, and part way does not seem practical.
What am I missing?
Posted by: ToppaTom | 27 December 2008 at 08:30 AM
Ok ill explain toppatom.
As far as the backers of h2 are concerned h2 is already a very useful and used substance. Its a HUGE industry and that industry being that huge deserves gov money toward making it work better during thing stage of the game.
This involves stuff like pipeline tech transport tech and the making and uses of h2.
Along the way cars get swept up in the deal simply because alot of what OTHERS are after with fuel cells and h2 production will result in a system that can handle cars.
Example 1 The elextrolysis machine. We NEED that or biofuel to h2 because we need h2 and cant count on natural gas for it forever. Some places right now cant use nat gas to make it and so we need less fossil fuel dependant ways to get h2.
So the need for h2 drives the work on elextrolysis without a car in sight.. Its important already.
Example 2 The fuel cell.. Industry has been wanting and NEEDING a better alternative to current apu tech and current backup power generation. The fuelcell is that and then some.
They also have needed a much more power dense mobile power source. Batteries failed by far to meet the NEED for a high power app. Fuel cells do the job rather well and just need work on mass production and durability. The car doesnt factor into it at all. They need it for other things first and foremost the car is just a sidebenifit.
example 3 Storage. They already store lots of h2 and in transporting it you obviously sometimes need to store it. So h2 storage tech is also independant of cars. It has to be done anyway.
The result is everything that is needed for an h2 car is not dependant on cars at all and thus is garanateed to come sooner or later no matter the price of gas no matter the market no matter what. Thats why its not a gamble its a sure thing.
Sooner or later the generation of h2 will be good and cheap enough because it has to get there anyway.
Sooner or later the storage problem will be licked because it already has to be.
And already we have to make better fuel cells anyway for uses other then cars so we can count on them getting there anyway.
The extra money pumped in just ensures it gets there faster wich makes all those others who need it anyway very happy.
Posted by: wintermane2000 | 27 December 2008 at 10:21 AM
Actually, I find it quite practical that I can plug-in my cell phone at home and don't need to go all the way to a gas-station 'to fill my cell phone up' - even if filling it up would only take 5 minutes.
I don't see why this would be completely different with cars.
Posted by: globi | 28 December 2008 at 05:13 AM
Because your cellphone battery doesnt cost 20 grand and weigh more then you do and take god knows how long to get a replacement shipped from urktakabutastan or whereever they are made.
Posted by: wintermane2000 | 28 December 2008 at 06:13 AM
The H2 industry does not deserve gov money just because it is huge any more than the sulfuric acid, ammonia, nitrogen and halogen industries deserve government money, just because they are huge.
I don’t know of any industries that need H2 to the degree that would justify the "government cost to support the transition ... $55 billion .. " as stated in the 30 DECEMBER 2008 GCC item “US Fuel Cell Council Pushes Congress for $1.17B for Hydrogen, Fuel Cell and Infrastructure Programs”.
The big cost hurdle is distribution.
H2 powered cars will be hard to sell when there are essentially no H2 gas stations.
H2 gas stations will be hard to sell when there are no H2 powered cars.
1. I don’t think electrolysis or natural gas conversion or other techniques for MAKING H2 are the issue. The lack of a distribution system and affordable fuel cells are.
2 Industry already has fuel cells. If industry needs better fuel cells (and if the car doesn’t factor into it) let industry develop them.
3 They already have ways to store H2. They are just not readily usable in cars.
Posted by: ToppaTom | 30 December 2008 at 09:47 PM
How do you know we arnt helping out those other industries too in standard tax funded blah blah blah yadda yadda yadda..
Hell we are prolly doing work on yak milk production for all we know.
Posted by: wintermane2000 | 30 December 2008 at 09:58 PM
The government program (YMP) to support Yak milk production is actually a bargain. Globally, ruminant livestock produce about 80 million metric tons of methane annually, accounting for about 28% of global methane emissions from human-related activities Because cows have four stomachs, they create considerably more of the gas than any other animal -- 75 percent of the total methane produced by all animals.
By supporting Yak milk production to the tune of 1.2M$ annually, the government is showing remarkable foresight.
Posted by: ToppaTom | 31 December 2008 at 10:48 PM
What realy scares me is Im not sure if you just made that up or if we realy are spending 1.2 mil a year on yak milk.
Posted by: wintermane2000 | 01 January 2009 at 11:05 AM
Nah, I just made it up - but we all have reason to be scared.
I agree that politics is too much about such things as earmarks for special interests.
Election and re-election are more important that whats best for the people.
Posted by: ToppaTom | 01 January 2009 at 12:36 PM
Heh almost got me there. Personaly I see it as a win win situation. At the very least fuel cell and h2 tech will reduce the energy and thus co2 intensity of the h2 we already are going to use and the power generation we already are going to need.
And in the process some cars will be able to go from gas/diesel to h2 that otherwise would have still been belching out alot more co2 otherwise.
Neither fuel cells nor batteries replace each other they just do a good job at what they do.
Posted by: wintermane2000 | 01 January 2009 at 04:05 PM