Molecular fuel cell catalysts hold promise for efficient energy storage

Precious metals such as platinum play an important role in the search for better and cheaper ways to store and utilize energy. They act as catalysts to propel the most efficient fuel cells, but they are expensive and rare.


Now, an alternative to non-metallic catalysts for fuel cells has emerged. In a study published July 15 in ACS Central Science, a team of chemists from the University of Wisconsin-Madison describes a new approach to replacing solid catalysts with a molecular catalyst system. While molecular catalysts have been explored before, earlier examples were significantly less efficient than traditional platinum catalysts.



Fuel cells convert chemical energy into electricity by reacting hydrogen and oxygen at two different electrodes. Catalysts make this reaction more efficient.

UW-Madison chemistry professor Shannon Stahl and laboratory researcher James Gerken drew inspiration from their group's previous work on catalysts for oxygen applications in the chemical industry. They noticed striking similarities between these aerobic oxidation reactions and the oxygen reactions in fuel cells, and decided to see if they could apply a similar approach to fuel cells.


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


"Although this catalyst combination has been used before in aerobic oxidation reactions, we didn't know if this would be a good fuel cell catalyst," Stahl said. "It turned out to be the most efficient reported to date. Molecular catalyst systems."


Since the method involves chemical reactions between gases, liquids and solids, it is no small feat to go from concept to demonstration. Gerken spent months researching and optimizing every component of the equipment they envisioned installing, before testing the model system.


"This work shows that, for the first time, molecular catalysts can approach platinum's efficiency," Gerken said. "And the benefit of molecular catalysts is that you can continue to modify their structure to achieve even higher efficiencies."


This work was supported by the U.S. Department of Energy through the Center for Molecular Electrocatalysis, Center for Frontier Research in Energy. Stahl and Gerken believe that the center can foster cross-cutting research among various chemical disciplines and open the way for future advances in the field.


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