University of Wisconsin-Madison (UWM) chemists have introduced a new fuel cell catalyst approach that uses a molecular catalyst system instead of solid catalysts. The team is on a quest for better, less expensive ways to store and use energy where platinum and other precious metals play an important role.

Platinum and other precious metals serve as catalysts to propel the most efficient fuel cells, but they are costly and rare. The UWM team looks to have a metal-free alternative catalyst for fuel cells that may be at hand.

In a study published July 15 in ACS Central Science, the team of introduced a new approach that uses a molecular catalyst system instead of precious metals. Although molecular catalysts have been explored before, earlier examples were much less efficient than the traditional platinum catalyst.

Fuel Cell Operation Diagram. Image Credit: UW-Madison.  Click image for the largest view.

Fuel Cell Operation Diagram. Image Credit: UW-Madison. Click image for the largest view.

The research may be important because a fuel cell converts chemical energy into electricity by reacting hydrogen and oxygen at two different electrodes and catalysts make the reactions more efficient.

UWM chemistry Professor Shannon Stahl and lab scientist James Gerken took inspiration from their group’s previous work with catalysts that use oxygen in applications for the chemical industry. They noticed a striking similarity between these aerobic oxidation reactions and the oxygen reaction in fuel cells and decided to see if they could apply a similar approach to a fuel cell.

The new catalyst is composed of a mixture of molecules called nitroxyls and nitrogen oxides. These molecular partners play well together; one reacts well with the electrode while the other reacts efficiently with the oxygen.

Professor Stahl said, “While this catalyst combination has been used previously in aerobic oxidations, we didn’t know if it would be a good fuel cell catalyst. It turns out that it is the most effective molecular catalyst system ever reported.”

Because the approach involves chemical reactions between gases, liquids and solids, moving from concept to demonstration was no small feat. Gerken spent months studying and optimizing each component of the setup they had envisioned before testing everything in a model system.

“This work shows for the first time that molecular catalysts can approach the efficiency of platinum,” Gerken said. “And the advantage of molecules is that you can continue to modify their structure to climb further up the mountain to achieve even better efficiency.”

This is one more breakout into the catalyst field that eventually will get to practical commercial fuel cells. Its interesting to see the team made the connection from industrial applications. The astonishing thing is the how effective the catalysts perform. For the catalyst community this is quite significant and for future consumers cause for more confidence on the new products to come.


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