Catalyst boost for DEFC development

Zhenxing Feng of the Oregon State University (OSU) College of Engineering helped lead the development of a catalyst that solves three key problems associated with DEFCs, namely low efficiency, the cost of catalytic materials and the toxicity of chemical reactions inside the cells.

Feng and collaborators at Oregon State, the University of Central Florida and the University of Pittsburgh found that adding fluorine atoms into palladium-nitrogen-carbon catalysts had positive effects, including keeping the cells stable for nearly 6,000 hours. The team’s findings have been published in Nature Energy.

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“To achieve carbon-neutral and zero-carbon-emissions goals, alternative energy conversion devices using the fuel from renewable and sustainable sources are urgently needed,” said Feng, an associate professor of chemical engineering. "Direct-ethanol fuel cells can potentially replace gasoline- and diesel-based energy conversion systems as power sources.”

Feng and collaborators are now seeking funding to develop DEFC prototypes for portable devices and vehicles.

“If this is successful, we can deliver a device for commercialisation in five years,” he said. “With more industrial collaborators, the DEFC vehicle can be implemented in 10 years, hopefully.”

Most of the ethanol produced in the United States is made in the Midwest, most typically from maize.

“In DEFC technology, ethanol can be generated from a number of sources, particularly biomass like sugar cane, wheat and corn,” Feng said. “The benefit of using biological sources to produce ethanol is that plants absorb atmospheric carbon dioxide.”

According to OSU, ethanol can deliver more energy per kilogram than fuels including methanol or pure hydrogen, and the infrastructure is in place to produce and distribute it.

“The first vehicle powered by an ethanol-based fuel cell was developed in 2007,” Feng said. “However, the further development of DEFC vehicles has significantly lagged due to the low efficiency of DEFC, the costs related to catalysts and the risk of catalyst poisoning from carbon monoxide produced in reactions inside the fuel cell.”

To tackle those problems the research team, which also included OSU’s Maoyu Wang and scientists from Southern University of Science and Technology in China and Argonne National Laboratory, developed high-performance palladium alloy catalysts that use less of the precious metal than current palladium-based catalysts.

Palladium, platinum and ruthenium are valued for their catalytic properties but are expensive and difficult to obtain.

“Our team showed that introducing fluorine atoms into palladium-nitrogen-carbon catalysts modifies the environment around the palladium, and that improves both activity and durability for two important reactions in the cell: the ethanol oxidation reaction and the oxygen reduction reaction,” Feng said. “Advanced synchrotron X-ray spectroscopy characterisations made at Argonne suggest that fluorine atom introduction creates a more nitrogen-rich palladium surface, which is favourable for catalysis. Durability is enhanced by inhibiting palladium migration and decreasing carbon corrosion.”

The research was supported by the US Department of Energy and National Science Foundation.