25 August 2005
Polymer Fuel Cell Breakthrough
by Kate Melville
The widespread use of fuel cells has, up until now, been hampered by the problem of operating temperature. While ceramic fuel cells demonstrate good efficiency, they operate at around 800 degrees Celsius, way too hot for appliances like cell phones and computers. Polymer fuel cells, on the other hand, operate at much lower temperatures but are much fussier about the quality of their fuel and consequently less efficient. But now, a new chemical has been identified that allows polymer fuel cells to run at moderate temperatures where the quality of the fuel becomes much less critical. The researchers believe this discovery could open the door to the widespread use of fuel cells as power sources for a whole raft of devices.
A fuel cell produces electricity by converting hydrogen and oxygen into water and harnessing the energy released in the reaction. To do this, fuel cells need a proton exchange membrane to conduct protons (positively charged ions) but block electrons. The exchange membrane is critical to the efficiency of the fuel cell.
The polymer electrolyte membranes (PEM) used up until now in fuel cells have several drawbacks. Their operating temperature is so low that even trace amounts of carbon monoxide in the hydrogen fuel will wreck 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 compared to traditional power sources. Additionally, while existing PEM fuel cells can operate at much lower temperatures, they are much less efficient than ceramic fuel cells. They must be kept relatively cool so that the membranes can retain the moisture they need to conduct protons. Consequently, polymer fuel cells were previously forced to operate at temperatures below 100 degrees Celsius.
Now however, 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 before and finally run at temperatures high enough to make them practical for everyday use. The team, lead by Dr. Meilin Liu, has discovered that a chemical called triazole is significantly more effective than other chemicals researchers have explored to increase conductivity and reduce moisture dependence in polymer membranes. And with triazole, the fuel cell can tolerate much higher levels of carbon monoxide in the hydrogen fuel.
According to the research, published in the Journal of the American Chemical Society, triazole PEMs allow the fuel cell operating temperature to be increased to above 120 degrees Celsius, whilst also 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."
"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. It's going to have a dramatic effect," concluded Liu.
Source: Georgia Tech
Pic courtesy Georgia Tech