Heat has always been a problem for fuel cells. There’susually either too much (ceramic fuel cells) for certain portable uses,such as automobiles or electronics, or too little (polymer fuel cells)to be efficient.
While polymer electrolyte membrane (PEM) fuelcells are widely considered the most promising fuel cells for portableuse, their low operating temperature and consequent low efficiency haveblocked their jump from promising technology to practical technology.
Butresearchers at the Georgia Institute of Technology have pinpointed achemical that could allow PEM fuel cells to operate at a much highertemperature without moisture, potentially meaning that polymer fuelcells could be made much more cheaply than ever before and finally runat temperatures high enough to make them practical for use in cars andsmall electronics.
A team lead by Dr. Meilin Liu, a professor inthe School of Materials Science and Engineering at Georgia Tech, hasdiscovered that a chemical called triazole is significantly moreeffective than similar chemicals researchers have explored to increaseconductivity and reduce moisture dependence in polymer membranes. Thefindings were published in the Journal of the American Chemical Society.
“Triazolewill greatly reduce many of the problems that have prevented polymerfuel cells from making their way into things like cars, cell phones andlaptops,” said Liu. “It’s going to have a dramatic effect.”
Afuel cell essentially produces electricity by converting the chemicalshydrogen and oxygen into water. To do this, the fuel cell needs aproton exchange membrane, a specially treated material that looks a lotlike plastic wrap, to conduct protons (positively charged ions) butblock electrons. This membrane is the key to building a better fuelcell.
Current PEMs used in fuel cells have several problems thatprevent them from wide use. First, their operating temperature is solow that even trace amounts of carbon monoxide in hydrogen fuel willpoison the fuel cell’s platinum catalyst. To avoid this contamination,the hydrogen fuel must go through a very expensive purification processthat makes fuel cells a pricey alternative to conventional batteries orgasoline-fueled engines. At higher temperatures, like those allowed bya membrane containing triazole, the fuel cell can tolerate much higherlevels of carbon monoxide in the hydrogen fuel.
The use oftriazole also solves one of the most persistent problems of fuel cells— heat. Ceramic fuel cells currently on the market run at a very hightemperature (about 800 degrees Celsius) and are too hot for mostportable applications such as small electronics.
While existingPEM fuel cells can operate at much lower temperatures, they are muchless efficient than ceramic fuel cells. Polymer fuel cell membranesmust be kept relatively cool so that membranes can retain the moisturethey need to conduct protons. To do this, polymer fuel cells werepreviously forced to operate at temperatures below 100 degrees Celsius.
Heatmust be removed from the fuel cells to keep them cool, and a waterbalance has to be maintained to ensure the required hydration of thePEMs. This increases the complexity of the fuel cell system andsignificantly reduces its overall efficiency. But by usingtriazole-containing PEMs, Liu’s team has been able to increase theirPEM fuel cell operating temperatures to above 120 degrees Celsius,eliminating the need for a water management system and dramaticallysimplifying the cooling system.
“We’re using the triazole to replace water,” Liu said. “By doing so, we can bring up the temperature significantly.”
Triazole is also a very stable chemical and fosters stable fuel cell operating conditions.
Whilethey have pushed their polymer fuel cells to 120 degrees Celsius withtriazole, Liu’s team is looking into better polymers to get thosetemperatures even higher, he said.
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