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Researchers discovered ideal particles size for catalyst inside a fuel cell

Researchers are working hard to develop hydrogen fuel cells as a viable method of powering automobiles. The problem with this type of fuel cell at this point is that the storage of hydrogen is difficult and the fuel cells don’t last as long as manufacturers would like.

Two scientists from the University of Wisconsin-Madison have made an important stride in making hydrogen fuel cell vehicles more viable. The two scientists -- Professor Dane Morgan and PhD student Edward Holby -- have designed a computational model that can optimize one of the most important components of a fuel cell, possibly leading to a longer usable life.

The computational model is being used to investigate how the particle size of a material relates to the overall stability of the material. The researchers are using the model to look at the most efficient and effective particle size for the catalyst inside the fuel cell.

The fuel cell catalyst is typically made from platinum or platinum alloy. The catalyst is used to aid the reaction between the protons, electronics, and oxygen at the cathode inside the cell. Platinum is able to withstand the corrosive fuel cell environment but is costly and not available in abundance.

Platinum particles used inside current fuel cell catalysts are as small as two nanometers across. The tiny particles offer enough surface area for the reaction, but are quickly destroyed and degrade rapidly. The degradation of the catalyst means that the fuel cell doesn't last long. The Department of Energy figures that a fuel cell needs to last for 7 months of continuous use for automotive needs.

The computational model developed by the pair has shown that the ideal particle size for the catalyst is about 20 atoms across, roughly twice as large as the particles inside fuel cells today. At the 20-atom size, the particles degrade much slower and allow the fuel cell to function significantly longer.

Morgan likens the stability of larger particles to cheese, "When you leave a large chunk of cheese out and the edges get crusty, the surface is destroyed, but you can cut that off and there is still a lot of cheese inside that is good. But if you crumble the cheese into tiny pieces and leave it out, you destroy all of your cheese because a larger fraction of the cheese is at the surface."

Another group of researchers made a breakthrough in July with the potential to make storing hydrogen for fuel cells more efficient.



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RE: Shows some promise
By randomly on 9/21/2009 9:48:49 AM , Rating: 2
Hydrogen fuel cell powered cars have a number of problems that are glossed over because they make a great 'Pollution free, Eco-Green' poster child. Few people actually in the industry believe hydrogen fuel cell cars will be deployed in any meaningful way for many many decades if ever. However they make a great marketing angle for getting 'Green' points for corporations, researchers can get grant money, news and magazines get wonderful articles about savior technologies.

1) There is no efficient way to make hydrogen other than reforming of natural gas at 80% efficiency. This does nothing to get you away from fossil fuels. In an MIT study even projecting improvements to fuel cells to 2020 a simple diesel hybrid car would still have better well to wheels performance than a fuel cell car.

2) Electrolysis is only about 50% efficient so using any source of electrical energy to make hydrogen to power your vehicle is grossly inefficient. 50% loss of energy in making the hydrogen, 12%-30%(compressed gas to liquid respectively)loss in energy in storing the hydrogen, 50% loss of energy in the fuel cell recovering the electricity. For an overall energy storage efficiency of less than 25%.

Compared to batteries with an overall storage efficiency in excess of 90%. That's 4 times the energy and energy cost to run a fuel cell vehicle vs a battery powered one.
That poor cycle efficiency means that you are always better off using your electrical power to do something else with until all your fossil fuel electrical power generation has been eliminated. Even then the economics of it weigh against fuel cells unless power costs get very cheap.

3)Hydrogen storage and transportation cost are quite high. Because pumps pump volume not density the costs of transporting hydrogen are energy intensive because even under very high pressure hydrogen has a very low density. This means it takes significant amounts of energy to pump the stuff around. You also would need to lay all new pipeline because existing pipeline is susceptible to hydrogen embrittlement. If you transport it by truck the low density hits you again. It takes 20 tanker trucks with the corresponding costs and energy usage to transport an equivalent amount of fuel as one gasoline tanker truck. Because you transport it as a compressed gas, every time you transfer it from one container to another you again incur pumping losses. If you deliver electical power to a 'gas station' and use electrolysis locally you need to lay all new powerlines to handle the load, you need to dissipate enormous amounts of heat at the station (half the energy put into electrolysis ends up as heat), and you spend another 12% of your energy compressing the gas (which generates even more heat). This become one very expensive gas station to build and maintain.
Hydrogen adsorption in solid materials is no better because usually the more hydrogen the material can adsorb the harder it gloms on to the hydrogen and the more energy it takes to get it back out again and you end up better off with compressed gas again.
4) Still huge problems with fuel cells. They are very expensive. They are delicate, you have to carefully control the amount of water in the system, if it dries out it destroys it. The catalysts are susceptible to poisoning from carbon monoxide and sulfur compounds in the air. They also don't last long enough and break down too rapidly.

Even though all these technical problems may be solvable in the future the basic thermodynamic efficiency limits of the overall energy cycle are constrained by theoretical limits, you just can't improve it all that much.

As to batteries
1) The waste disposal problem is largely a red herring. The batteries would be recycled. The retained value of large lithium batteries from cars would be in the hundreds of dollars for the materials alone. End of life capacity is considered to be 80%, the value of a still functional battery with 80% capacity would be in excess of a thousand dollars. Nobody is going to dump them in land fills, and if they do somebody is going to pick them up and sell them.

2) The Silicon nanowire lithium battery thing is constantly misrepresented by the press. The density was only 10x on the very first charge, for repeated cycles it was 8x. But the real deception is that this is for the Anode of the battery only, not the cathode. Current Anode materials (usually graphite) already have several times more capacity than the cathode materials. Even if the silicon nanowires could store 100X the density it wouldn't improve the capacity of lithium batteries more than about 1/3 because the bottle neck is the cathode materials.
But of course that doesn't make as sensational a story, and it's not about truth in science, it's about readership.


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