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Fuel Cell Challenges

The challenges and barriers to commercializing PEM based fuel cells are many. They have been outlined in a report by the Department of Energy, Basic Research Needs for the Hydrogen Economy and in a number of publications.

PEM fuel cells have limited durability, especially when used in a frequent on-off mode and when the power output changes significantly and frequently, as would happen if the fuel cell were the only power source in a transportation vehicle or in fact in many portable applications. Currently, automotive fuel cells have difficulty reaching 1000 hours of use before failure. At least 5000 hours of use is needed for consumer acceptance (this translates to somewhat more than 100,000 miles of use averaged over typical driving modes and traffic conditions). The durability problems are related to shortcomings of the materials used in the Membrane Electrode Assembly (MEA): the catalysts, the membrane and the catalyst support. Further, the highest efficiency fuel cells can only use very pure hydrogen as the fuel. Such hydrogen is very expensive.

When there are impurities in the hydrogen, such as sulfur or carbon monoxide, the platinum anode catalyst is poisoned; that is, it is coated with the impurities and the catalytic activity is reduced or altogether lost. Such poisoning leads to further efficiency loss as well as complete cell failure.

At the cathode, the potentials are high enough to cause corrosion of the carbon black support as well as dissolution and re-precipitation of the platinum catalyst. When the carbon black corrodes, the catalysts become separated from the support. The corrosion is even thought to be accelerated by the presence of the catalyst. When the platinum re-precipitates, it often does so away from the electrode, such as in the membrane, where it can no longer contribute to the electrochemical reduction of oxygen. Even if it stays in the cathode, the particle size grows through this process. This causes a loss of surface area and reactivity when measured as activity per gram of platinum.

The membranes also chemically degrade, allowing large holes to form between the cathode and anode. This produces an explosion hazard as well as rapid cell failure.

The above problems can only be partially mitigated by re-engineering the fuel cell system and the fuel cell controls. It is generally agreed that new materials are needed to address the shortcomings of materials presently used and to reach higher efficiency and lower fuel cell costs.

Our Aim

Our goal is to develop new materials for fuel cell technology. Our main research efforts are in developing new electrocatalysts for both fuel cell anodes and cathodes as well as conducting support materials for these electrocatalysts. Our catalysts are made from a class of materials known as "ordered intermetallics" in which two or more transition metals are bound in an ordered lattice rather than in an alloy or solid solution which has a random arrangement of atoms. Additionally we are developing combinatorial testing methods that enable the electrochemical testing of hundreds of potential catalysts with high throughput. The catalyst supports we're are developing are based on TiO2 and Nb2O5 doped with other transition metals. Current catalyst supports are based on carbon-black which tends to oxidize at the potentials used in a fuel cell resulting in poisoning of the Pt catalysts by carbon monoxide. Our supports are carbon free and lead to no poisoning at all!

Our Challenges

Our intermetallic catalysts are designed to contain only metals and nothing else. Usually when synthesizing a materials in open air the surfaces of the product materials are coated with an oxide layer and other impurities that are present in the air, Therefore our catalysts must be prepared in a completely air-free environment, a relatively simple prospect on the laboratory scale, but somewhat difficult if our catalysts prove to be sufficiently active for commercial applications. Additionally Pt is still a major component of our catalysts and remains one of the most expensive materials in the world. Ideally a new catalysts would be Pt free, but we and others have yet to find a viable alternative to the current catalysts in use in industry and the few fuel cells that are available commercially. We are working toward developing new intermetallic compounds with superior activity and ease of use.

Our supports are based on TiO2 and Nb2O5; two oxides that are insulating. By doping with transition metals like tungsten, molybdenum, and others we are able to induce conductivity and take advantage of the high strength and stability of titania and niobia. We are working on both high temperature synthesis and sol gel synthesis techniques to make these novel supports and are making great progress. However, the conductivity of our supports needs to be improved in order for them to serve as an alternative to carbonaceous supports.


Equinox

Fuel Cell Powerd Chevy Equinox-
Many people think of fuel cells as
the next power source for
automobiles.

Angstrom

Fuel Cells can also be adapted to
power devices such as cell phones, laptops, and mp3 players.