|Protons hop from one triazole group (the blue spheres) to another to move through the PEM without the need of water.|
Researchers at the Georgia Institute of Technology have identified a chemical that could allow PEM (polymer electrolyte membrane) fuel cells to operate at a higher temperatures without moisture.
This could lead to polymer fuel cells that are more simple in design (and less expensive) and able to run at temperatures high enough to make them more efficient for use in cars and small electronics.
A team led by Dr. Meilin Liu, a professor in the School of Materials Science and Engineering at Georgia Tech, has discovered that triazole is significantly more effective than similar chemicals researchers have explored to increase conductivity and reduce moisture dependence in polymer membranes.
The findings were published in the Journal of the American Chemical Society.
The conductivities of a poly(4-vinyl-1H-1,2,3-triazole) membrane without any acidic dopants are about 105 times greater than those of poly(4-vinylimidazole) in dry air at 50º–150º C. Polymers with groups promoting proton conduction attached to the backbone have great potential to offer excellent mechanical properties and long-term stability. Further, 1H-1,2,3-triazole and PEMs containing 1H-1,2,3-triazole are stable in a wide potential range, implying excellent electrochemical stability under fuel cell operating conditions.—From the paper’s abstract
While polymer electrolyte membrane (PEM) fuel cells are widely considered the most promising fuel cells for mobile use, their low operating temperature and relatively low efficiency have retarded their jump from promising to practical.
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.—Dr. Meilin Liu
The exchange membrane in a PEM fuel cell serves to conduct protons (positively charged ions) but to block electrons. Membrane quality is key to a better fuel cell.
Most PEMs used in current fuel cells have several problems. 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 must be purified—an expensive process that drives up the overall cost of the system. At higher temperatures, however, like those allowed by a membrane containing triazole, the fuel cell can tolerate higher levels of carbon monoxide in the hydrogen fuel.
Second, although the lower operating temperature of PEM fuel cells compared to ceramic fuel cells makes them applicable for use in mobile applications, they are also less efficient than ceramic fuel cells. Polymer fuel cell membranes operate at temperatures below 100º C so that membranes can retain the moisture they need to conduct protons.
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 reduces its overall efficiency.
But by using triazole-containing PEMs, Liu’s team was able to increase their PEM fuel cell operating temperatures to above 120º C, eliminating the need for a water management system and dramatically simplifying the cooling system.
We’re using the triazole to replace water. By doing so, we can bring up the temperature significantly.—Dr. Meilin Liu
For the research, the team embedded triazole into a sulfonated polysulfone (sPSU) polymer (basically by immersing the polymer in liquid triazole for 24 hours under heat).
Liu’s team is now looking into better polymers to push operating temperatures even higher.
Promotion of Proton Conduction in Polymer Electrolyte Membranes by 1H-1,2,3-Triazole; Zhou, Z.; Li, S.; Zhang, Y.; Liu, M.; Li, W.; J. Am. Chem. Soc.; (Communication); 2005; 127(31); 10824-10825.