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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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RE: Please pull this through
By randomly on 2/17/2009 2:23:07 PM , Rating: 2
Unlike oil though the Lithium isn't consumed and it can be recycled out of the old batteries which almost certainly will happen because of the high dollar value of the resources in a used electric car battery.
Also a rule of thumb for mined resources is that doubling the market price increases the extractable reserves by a factor of 10 as less concentrated mining sources become economically viable.

Hydrogen as an energy carrier has so many unresolved problems that it's implementation as the 'fuel of the future' seems unlikely at this point.

1) Storable density is low.
There is less hydrogen in a gallon of liquid hydrogen than in a gallon of gas. However it would be workable except for the very high energy cost of liquefying the hydrogen. It takes 30% of the available energy in the hydrogen to liquefy it at 20 degrees above absolute zero. You also have the problem of significant fuel boil-off from heat soaking into the Dewar. The best solution so far available is compressed gas, or chilled compressed gas cylinders. They only have a 12-15% energy cost but the fuel density is much lower, the tanks are heavy, and at 5000-10,000 PSI they are a real safety concern in case of tank failure. Also unlike a liquid fuel working with gaseous Hydrogen you incur significant pumping energy costs every time you transfer fuel from a hydrogen production facility to a tanker truck, tanker truck to refueling station, station to vehicle tanks.

Using materials that can adsorb a few percent by weight of hydrogen, such as paladium, is interesting science but all those materials require considerable energy input to get the hydrogen back out of the material since these materials all glom onto the hydrogen pretty hard and the energy efficiency is again so dismal as to make them unworkable. That's even before you get into the longevity, excessive weight and terrible economics of such approaches.

The gallium-aluminum fuel approach also just doesn't work because of the terrible energy efficiency of the cycle.

Fuel transport costs are high. Because the density is so low it takes considerable energy even to pump the hydrogen around in pipelines. For a gas station that can be supplied by one tanker truck of gasoline a day, to deliver the same fuel energy with hydrogen it would take 20 tanker trucks a day.

2) Hydrogen production is inefficient.
Electrolysis is only about 50% efficient. That coupled with the fuel cell efficiency of about 50% means it takes 4 KwH of electricity from the power station to deliver 1 KwH of electricity at the vehicle motor. 25% round trip efficiency for an energy storage system isn't too good. Lithium batteries with a round trip charge/discharge efficiency in excess of 90% will give you 4 times the mileage of a Hydrogen system. In fact generating hydrogen from electricity is almost always an economically poor idea since there are almost always better places to use that electricity directly. Using solar cells to make hydrogen is just a PR stunt since it makes no economic sense whatsoever compared to putting that electricity into the grid and displacing some fossil fuel generated power.
The only efficient way to produce hydrogen is by reforming natural gas, at 80%+ efficiency. However this does nothing to get you off fossil fuels, or minimize carbon footprint since as pointed out in an MIT study that even by 2020 hydrogen fuel cell vehicles will still be less efficient well to wheels than a simple cheap Diesel hybrid vehicle.

The one economically realistic future option for non-fossil fuel derived hydrogen is by using Very High Temperature nuclear reactors and a sulfur-iodine cycle. However developing the reactors and hydrogen technology to the point of commercial deployment will take 20-30 years.

3) Fuel cells are bulky, heavy, expensive, delicate, and don't last long enough. The catalysts are expensive. They are also easily poisoned by carbon monoxide and sulfur compounds so the hydrogen and oxygen (derived from air) have to be purified and monitored. The water management has to be controlled so the cell neither floods or dries out (which ruins it). You can't let it freeze, or it destroys the cell. The membranes just don't last long enough, you'll have to replace them multiple times during the life of a vehicle. All these points are probably solvable to some degree given enough research and development but fuel cells won't be economically deployable for vehicles for many years to come.

4) There is no hydrogen infrastructure. There are no hydrogen production facilities( other than natural gas ones). There are no distribution systems either trucks or pipelines. Existing pipelines can't be used because of hydrogen embrittlement of the metal, you have to lay all new lines. There are no hydrogen fuel stations, no hydrogen distribution tankers. You can't even use local electrolysis supplied by the electrical grid to generate hydrogen locally to any significant degree because the grid is incapable of those levels of power transfer.

The general population are almost totally unaware of all these issues. Car manufacturers and energy companies tend to use the technology only for green washing, gaining eco-friendly PR points with demonstration vehicles and fueling stations that in reality will never be deployed in useful numbers because they are too expensive and too inefficient. Researchers also trumpet this stuff regularly in order to get funding, as do companies looking for investors.

Is it possible that a number of unimagined huge breakthroughs will make hydrogen fuel viable? It's possible, but at this point it seems an uphill climb and not the way to bet. Advancing battery technology and ultracapacitors have many fewer hurdles to overcome and seem a more likely solution for passenger cars and vehicles that do not require a great deal of energy density. Fossil fuels will probably reign supreme for trucks, ships and planes for a long time to come, even if it comes to synthesizing the fuel instead of pumping it out of the ground. It's very hard to beat the energy density, portability, and ease of handling of petroleum fuels. Long haul trucks and trains may trend toward electric on special roads and tracks that can supply an electrical connection, with fossil fuel supplement when the vehicle leaves that grid.

I'm certainly in favor of continued research, but you also have to be realistic, look at the overall picture, and not get emotionally attached to a single approach. Sometimes things just don't work out, no matter how cool they seemed at first.


RE: Please pull this through
By freeagle on 2/17/2009 2:41:54 PM , Rating: 2
Too bad many will skip this post for its length. They'll miss a lot


RE: Please pull this through
By Regs on 2/18/2009 1:12:27 PM , Rating: 2
No, many of us read it. Though it would take a reply twice as long to argue.


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