Better Than PEM? | Green Energy News

November 16, 2003 – Vol.8 No.34

BETTER THAN PEM?

Researchers at CalTech have reportedly developed a type of PEM (proton exchange membrane or polymer electrolyte membrane) that uses a solid acid membrane in place of the water-moistened polymer membrane. The CalTech fuel cells operate on methanol, not hydrogen.

Water is a byproduct of the combining of hydrogen and oxygen in a fuel cell. But some water is also retained within the fuel cell stack to keep the membranes moist. Water allows charged particles, or ions, to pass through the membrane.

But it is also the water-to-keep-the-membranes-moist that creates problems for the fuel cells. One side of the membrane can dry out and on the other side water builds up and must be discharged from the fuel cell stack. Water inside the fuel cell limits its operating temperature range. Too cold, and water in the stack freezes. (Honda has apparently solved the freezing fuel cell problem, though hasn't publicized exactly how.)

The use of solid acid for membranes allows ions to pass through, thus no need for water moistened membranes. And the design would allow a liquid fuel - methanol in this case - to operate the fuel cell without conversion to hydrogen gas.

True, methanol is typically made from fossil fuels, but it can be made from renewable feedstock. But it is also true that most hydrogen (at least in the beginning stages of the so-called hydrogen economy) would be extracted from natural gas. (Hopefully, renewable hydrogen would be developed over time.)

The methanol-fueled solid acid fuel cell would also emit carbon dioxide, but the greater efficiency of the electrically driven, fuel cell energized vehicle would significantly reduce the greenhouse gas emissions. And if methanol were derived from renewable sources it would be a carbon-neutral fuel.

But what would be the best advantages of this technology? Hydrogen storage on board a vehicle and at filling stations - which is difficult - isn’t an issue. Methanol just needs a tank. And a methanol infrastructure would be easy and cheap to build - another fuel tank and pump at the local filling station will do.

At this time all this may be a dream. The solid acid fuel cell is only an experiment - for now. Visit CalTech Center for Science and Engineering of Materials at http://www.csem.caltech.edu/teaching.html