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New material should give a boost to the hydrogen economy

Many believe that hydrogen is the eventual replacement for gasoline and that future vehicles will be fuel cell-based plug-in hybrids.  However, in order to transition to such a hydrogen-based economy, many key challenges remain.  The biggest challenges are devising and implementing means to make, store, and ship hydrogen to distribution centers.

One of the key challenges in making hydrogen is the need for purification.  Many chemical reactions that produce hydrogen also produce a mixture of hydrocarbon gases and water vapor.  In the past separating these substances has been a tricky and inefficient process.

Now chemists at Northwestern University have developed a class of porous materials that may solve this problem by letting hydrogen gas through selectively, while impeding other gases.  According to the researchers, the materials exhibit the best known selectivity towards hydrogen over methane and carbon dioxide of any known material.

Mercouri G. Kanatzidis, a professor of chemistry at the university and co-developer of the material, states, "A more selective process means fewer cycles to produce pure hydrogen, increasing efficiency.  Our materials could be used very effectively as membranes for gas separation. We have demonstrated their superior performance."

While current separation techniques rely on separating molecules by size, the new porous membrane material separates them by polarizability.  The new membrane, composed of germanium, lead and tellurium, lets hydrogen through faster, as it is a hard, small molecule which interacts little with the charged walls.  The membrane is a hexagonal nanoporous structure, with parallel tubes about two to three nanometers wide.  The gas molecules are at least half a nanometer wide.  The membrane selects hydrogen at a rate approximately four times higher than the current best methods.

Professor Kanatzidis describes the material stating, "We are taking advantage of what we call 'soft' atoms, which form the membrane's walls.  These soft-wall atoms like to interact with other soft molecules passing by, slowing them down as they pass through the membrane. Hydrogen, the smallest element, is a 'hard' molecule. It zips right through while softer molecules, like carbon dioxide and methane take more time."

The membrane operates within a "convenient temperature range" of zero degrees Celsius and room temperature.

Professor Kanatzidis worked closely with postdoctoral research associate Gerasimos S. Armatas on developing and testing the material.  The pair has published a paper entitled "Mesoporous Germanium-Rich Chalcogenido Frameworks with Highly Polarizable Surfaces and Relevance to Gas Separation".  It is published online at the journal Nature Materials.

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stupid question...
By jaybuffet on 2/17/2009 9:27:45 AM , Rating: 2
Why can't we have a hydrogen tank in our cars and simply fill up at home using electrolysis?

RE: stupid question...
By freeagle on 2/17/2009 9:43:26 AM , Rating: 3
1) Because storing hydrogen in a liquid form is not an efficient storage. Gasoline contains more hydrogen than the same volume of pure liquid hydrogen. The distance you could drive with full tank would decrease significantly.

2) It's much more expensive to have several thousands/millions of small devices for producing hydrogen through electrolysis than to have a few factories specialized on it.

RE: stupid question...
By jaybuffet on 2/17/2009 9:56:03 AM , Rating: 1
I was talking about splitting water into hydrogen at home using electrolysis. How much hydrogen gas would one need to travel 80 miles? Wouldn't hydrogen gas also make your car weigh less making it a little more efficient? You could come home, connect your car to a machine which simply splits water into H2 and O. When you wake up, your car is filled. I'm sure someone has thought of this, and it's probably been proven as not feasible, but i am wondering why?

RE: stupid question...
By freeagle on 2/17/2009 10:08:44 AM , Rating: 3
I was talking about splitting water into hydrogen at home using electrolysis

I don't see in what way was I talking about something else.

Wouldn't hydrogen gas also make your car weigh less making it a little more efficient?

The weight of a full tank is only a minor fraction of the weight of whole vehicle. Even if liquid hydrogen weighted nothing, the gained efficiency would not be very noticeable.

probably been proven as not feasible

As far as I know, current methods of hydrogen production are not very efficient. You'd lost a lot of energy producing the hydrogen, which rather could be stored in a battery and used directly.

RE: stupid question...
By jaybuffet on 2/17/2009 10:32:29 AM , Rating: 2
Ok so I stopped being lazy and did a few quick calcs.. if I wanted to travel 90 miles a day in a car which gets 30 mpg.. to get the equivalent energy, i would need about 388ft^3 of H2... thats a lot of H2 in gas form.. (~5ftx2ftx2ft) but couldnt a car be designed around that? plus h2 is lighter than air so yes it would be lighter than gas, and wouldnt it also lift the car slightly reducing the weight even more. (here are the numbers i used: Gas weighs about 3kg/gal, energy - 46.9 MJ/kg. Hydrogen energy - 143 MJ/kg, density - .0899 kg/m3)

RE: stupid question...
By jaybuffet on 2/17/2009 10:38:45 AM , Rating: 2
ok maybe 388ft^3 is more like 4ft x 5ft x 2ft.. i've been out of school for too long.. but still..

RE: stupid question...
By freeagle on 2/17/2009 10:54:18 AM , Rating: 2
or maybe something like 10ft x 10ft x 3.88ft.

and wouldnt it also lift the car slightly reducing the weight even more

If you put that big balloon of hydrogen above it, then it would get a bit of lift (don't have time to calculate how much), but the weight would not be reduced. The lighter hydrogen would be pulled upwards in the heavier atmosphere, which would make it look like it weights less. You'd also loose a lot of grip due to this, so your efficiency would decrease drastically, because the tires and their contact with the road transforms the rotational energy produced by motor into a force pushing your car forward. The car would also be a lot less maneuverable.

RE: stupid question...
By jaybuffet on 2/17/2009 10:59:20 AM , Rating: 2
A quick search on google turned up a 0.158 kw hours per cubic foot number for generating hydrogen from water using electrolysis. If this is true, then I would need 61.3 kwh to fill 388ft^3. My coned bill says a kwh costs me $.12. So that would equate to $7.36 to go 90 miles (if this was gas, and i'm getting 30mpg, thats equivalent to $2.45/gal)

RE: stupid question...
By freeagle on 2/17/2009 11:06:08 AM , Rating: 2
But that only calculates the cost of produced hydrogen. You need additional energy to squeeze the 388ft^3 of hydrogen into a conventionally sized tank. My guess it won't be very cheap.

RE: stupid question...
By jaybuffet on 2/17/2009 11:16:59 AM , Rating: 2
who says we need a conventional tank :-) lets throw a tank on the roof.. there enough space up there for a tank 5ft wide, 4ft long, 2ft tall.... might look goofy in the beginning.. but what doesnt..

RE: stupid question...
By freeagle on 2/17/2009 11:22:01 AM , Rating: 2
Since you've been talking about reducing weight.... do you realize that 5x4x2 ft tank for storing pressurized hydrogen would add significant amount of weight to the car?

RE: stupid question...
By jaybuffet on 2/17/2009 11:32:34 AM , Rating: 2
not pressurized... but the weight reduction seem moot (another site said 1 ft^3 at STP lifts 0.07lbs, so 388ft^3 would only lift 27lbs, probably less than the container)

this sounds too feasible.. i must have messed up a calc somewhere

RE: stupid question...
By freeagle on 2/17/2009 11:38:55 AM , Rating: 2
not pressurized

5x4x2 ft can store only 5x5x2ft^3 of unpressurized H2. If you wan to put 388ft^3 of into that space, it has to be under pressure

RE: stupid question...
By jaybuffet on 2/17/2009 11:48:51 AM , Rating: 2
i'm dumb +1. So anyways, i wonder how much energy that would take to compress the hydrogen. I guess thats what this whole issue is about... hydrogen storage.. that took a long time for me to get it

RE: stupid question...
By freeagle on 2/17/2009 11:55:51 AM , Rating: 2
The whole issue is about efficient production and storage. We need to store much more hydrogen than those 388ft^3 you calculated, because 90 miles driving distance is not much compared to what you get with full tank of gasoline. We also need to figure out a way to cheaply produce a lot of hydrogen. For now, storing the energy in batteries is more effective.

RE: stupid question...
By jaybuffet on 2/17/2009 12:03:27 PM , Rating: 2
i would think 90 miles would be more than enough for peoples daily driver. i mean, my calculation came to the equivalent of $2.45 per gal of gas.. which isn't too bad.. add on the cost of compressing it.. not sure what is involved there cost wise.. i wouldn't think it would be substantial since we're not talking a huge compression (10:1), though i could be wrong. at least we would reduce our dependency on foreign oil.. efficiencies can only go up.. (gov't wouldn't get its taxes though, so they would probably make the production of hydrogen illegal much like marijuana)

RE: stupid question...
By codeThug on 2/17/2009 4:31:10 PM , Rating: 2
stop. stop.

I can't take anymore...

RE: stupid question...
By monomer on 2/17/2009 12:25:57 PM , Rating: 2
Even if the hydrogen under pressure was lighter than air, you're neglecting the fact that the hydrogen sill has mass, which takes energy to accelerate.

All the reduction in weight would do is reduce friction between the car and the road, which is good while rolling, but bad while accelerating.

RE: stupid question...
By DaveLessnau on 2/17/2009 10:00:40 AM , Rating: 2
Thanks for that information. I had assumed that the energy content of hydrogen was higher than gasoline's regardless of the form. Here's a link that gives numbers to support your statement:

RE: stupid question...
By nafhan on 2/17/2009 10:05:13 AM , Rating: 3
You can do that now with our current tech.
The problem is that you wouldn't want to. Electrolysis and hydrogen storage are, respectively, expensive and bulky compared to just using electricity and batteries.
A lot of people forget that hydrogen cannot be found lying around under the ground like gasoline can. When burning gasoline, you can actually get back more energy than it took to extract it from the ground, because the energy from decaying plant matter, etc. has been stored in the crude oil. When burning hydrogen this will never happen because we have to create the hydrogen in energy intensive processes such as electrolysis, which thanks to the laws of thermodynamics we know will never make back more energy than we put into it.

RE: stupid question...
By ironargonaut on 2/18/2009 1:43:39 AM , Rating: 2
What would that solve? Energy is neither created nor destroyed. I believe it is a law. The energy you can get from combining H+H+O->H20 can never be more then the energy it takes to reverse the process H2O->H+H+O. Otherwise you could make a perpetual motion machine by cycling the process. Therefore, without doing any math one can see that taking into account efficiency of electrolysis and efficiency of power line transmissions. It takes more energy to create the hydrogen gas than it can be gained from it. Assuming 100% efficent engine. The extra energy to create the electricity will come from the burning of fossil fuels since green energy can not supply current demand. This is ignoring storage and other issues.
Tne net result is if all vehicles could switch tomorrow to hydrogen more fossil fuels would be needed to keep them running or more nuclear reactors.
Perhaps someday someone will create a plankton that uses the suns energy to create hydrogen from H20. But, would it be more or less efficent than solar cells?
My question is if CO2 is so bad how come we don't cap the coal mine fires that spew as much CO2 as all the cars in the US?

"The Space Elevator will be built about 50 years after everyone stops laughing" -- Sir Arthur C. Clarke

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