University of Calgary

Metal-organic materials may drive cheaper fuel cell vehicles

UToday HomeJuly 31, 2013

By Mark Lowey

George Shimizu, professor in the Department of Chemistry, worked on the research with graduate students Jared M. Taylor and SiRim Kim.George Shimizu, professor in the Department of Chemistry, worked on the research with graduate students Jared M. Taylor and SiRim Kim.Crystal-like materials that can be designed and built atom-by-atom may hold the key to making fuel cells affordable and widely used – including for vehicles.

University of Calgary scientists, who are global leaders in building the materials called Metal-Organic Frameworks (MOFs), say further development of micro-porous, crystalline MOFs for fuel cells could significantly lower the cost of the clean energy technology.

In a “boldly optimistic scenario, MOFs could be used for all parts of a fuel cell . . .,” university researcher George Shimizu and graduate students Jared M. Taylor and SiRim Kim say in an invited “Perspectives” paper published this month in the top-ranked journal Science.

Unlike conventional materials, MOFs are “scaffolding” on a molecular level, “with the advantages that they are very ordered and you can get molecular-level images of them,” says Shimizu, professor of chemistry and associate dean in the Faculty of Science.

“You know the exact structure of what you’ve made, so you can design it, evaluate exactly what you’ve done and then go back to the design and improve it,” he says.

In their Science paper, “Proton conduction with metal-organic frameworks ,” Shimizu and his team say that with further development, MOFs could be used to make a crucial component in proton-exchange membrane (PEM) fuel cells – the electrolyte membrane that completes the cell’s electronic circuit by conducting protons.

A fuel cell converts chemical energy (hydrogen and oxygen) into water and electrical energy. Water carries the ions (protons) in a PEM fuel cell, of which the core components are the electrolyte membrane and the two electrodes.

PEM fuel cells are being used in fuel cell vehicles. However, the polymers (plastic compounds) now used to make the electrolyte membrane limit the fuel cells’ efficiency to lower operating temperatures, and the rare metal platinum used in the electrodes makes the technology too costly for widespread use.

“In the best-case scenario, if you could run at higher temperatures, you could use a much cheaper metal for the electrodes or use a lot less platinum,” Shimizu explains.

Critics of using MOFs in fuel cells have argued that the crystalline materials, with extremely tiny (billionths of a metre) pore spaces, wouldn’t be able to conduct enough protons or be stable in water at temperatures above 80° C.

But Shimizu’s team, in work published in two papers earlier this year in the Journal of the American Chemical Society, produced a system with the highest level of proton conduction ever reported in a MOF (two orders of magnitude higher), as well as another MOF system with good proton conduction that was stable in boiling water (100° C).

The team is now working on overcoming the inherent brittleness of MOFs to make them more plastic-like and able to handle mechanical stress, Shimizu says. “If we could make things that we could bow and bend just a little bit, that would be a very big breakthrough.”

 

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