Proton Exchange Membran

Heat has always been a problem for fuel cells. There’s usually 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) fuel cells are widely considered the most promising fuel cells for portable use, their low operating temperature and consequent low efficiency have blocked their jump from promising technology to practical technology.

The diagram represents a fuel cell’s polymer electrolyte membrane (PEM) with the proton-conducting group triazole (the circles in the diagram). Protons hop from one group to another to move through the PEM without the need of water. (Diagram and information are courtesty of Georgia Institute of Technology.) +

But researchers at the Georgia Institute of Technology have pinpointed a chemical that could allow PEM fuel cells to operate at a much higher temperature without moisture, potentially meaning that polymer fuel cells could be made much more cheaply than ever before and finally run at temperatures high enough to make them practical for use in cars and small electronics.

A team lead by Dr. Meilin Liu, a professor in the School of Materials Science and Engineering at Georgia Tech, has discovered that a chemical called triazole is significantly more effective than similar chemicals researchers have explored to increase conductivity and reduce moisture dependence in polymer membranes.

“Triazole will greatly reduce many of the problems that have prevented polymer fuel cells from making their way into things like cars, cell phones and laptops,” said Liu. “It’s going to have a dramatic effect.”

A fuel cell essentially produces electricity by converting the chemicals hydrogen and oxygen into water. To do this, the fuel cell needs a proton exchange membrane, a specially treated material that looks a lot like plastic wrap, to conduct protons (positively charged ions) but block electrons. This membrane is the key to building a better fuel cell.

Current PEMs used in fuel cells have several problems that prevent them from wide use. First, their operating temperature is so low that even trace amounts of carbon monoxide in hydrogen fuel will poison the fuel cell’s platinum catalyst. To avoid this contamination, the hydrogen fuel must go through a very expensive purification process that makes fuel cells a pricey alternative to conventional batteries or gasoline-fueled engines. At higher temperatures, like those allowed by a membrane containing triazole, the fuel cell can tolerate much higher levels of carbon monoxide in the hydrogen fuel.

The use of triazole also solves one of the most persistent problems of fuel cells — heat. Ceramic fuel cells currently on the market run at a very high temperature (about 8000 Celsius) and are too hot for most portable applications such as small electronics.

While existing PEM fuel cells can operate at much lower temperatures, they are much less efficient than ceramic fuel cells. Polymer fuel cell membranes must be kept relatively cool so that membranes can retain the moisture they need to conduct protons. To do this, polymer fuel cells were previously forced to operate at temperatures below 1000 C.

Heat must be removed from the fuel cells to keep them cool, and a water balance has to be maintained to ensure the required hydration of the PEMs. This increases the complexity of the fuel cell system and significantly reduces its overall efficiency. But by using triazole-containing PEMs, Liu’s team has been able to increase their PEM fuel cell operating temperatures to above 1200 C., eliminating the need for a water management system and dramatically simplifying the cooling system.

“We’re using the triazole to replace water,” Liu said. “By doing so, we can bring up the temperature significantly.”

While they have pushed their polymer fuel cells to 1200 C with triazole, Liu’s team is looking into better polymers to get those temperatures even higher, he said.

A micro sized version of a tubular PEM fuel cell is proposed, and because of the small size, it could produce from ten to 60 times the power density of plate and frame PEM fuel cells which nominally produce 0.1 W/g and 0.1 kW/L.

(Sept. 2003) T/J Technologies is awarded A National Science Foundation contract for a fuel cell program, “Bimetallic Oxygen Reduction Catalysts for Proton Exchange Membrane (PEM) Fuel Cells.” This program focuses on developing and demonstrating a new electro catalyst that increases the power density and decreases the costs of the fuel cells. The underlying purpose is to make fuel cells affordable for commercial viability.

(Sept. 2003) The U.S. Department of Defense has published a final report on the one-year demonstration of a residential fuel cell for military facilities. The 3-kiloWatt hydrogen PEM fuel cell developed by AVISTA Labs was installed and operated at the Geiger Field, 242nd Combat Communications Squadron’s building 401. The fuel cell, which ran for over 8.8760 hours, exceeded the 90% availability requirement. For more information, see http://wwwdodfuelcell.com/res/GeigerUpdatedFinalReport.pdf.

(August 2003) Sanyo Electric and Hoku Scientific join to develop a new membrane electrode assembly technology for use in Sanyo’s Proton Exchange Membrane (PEM) fuel cell. The targeted application is for stationary power markets. PEM fuel cell could begin supplementing conventional power production as early as 2005 in Japan.