Organic Rankine Cycle
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Although the fuel cell described produces a relatively low voltage, several fuel cells of this kind can be wired in series to produce higher voltages and do useful work.
The PEM Material
The PEM (proton exchange membrane) material is a perfluorosulfonic acid polymer film. Several manufacturers make PEMs in one form or another. We used one made by du Pont called Nafion 117. Nafion 117 is a transparent polymer film about 175 microns (0.007 inches) thick. Dow Chemical Co., Asahi Chemical Co., and Chloride Engineers Ltd. make something similar. A patent describing how one PEM manufacturer’s film is processed is listed in the references section at the end of this article.
The basic structural unit formula for Nafion 117 is shown below:
CF = CFOCF CFOCF CF SO H 22223
Nafion 117 contains fluorine, carbon, oxygen, sulfur, and hydrogen arranged in repeating polymer molecules. The hydrogen atom on the SO3 part of the molecule can detach from one SO3 site. The free H+ proton can hop from SO3 site to SO3 site through the material, to emerge on the other side of the membrane. This is the reason it is called a proton exchange membrane. It can be thought of as solid sulfuric acid, an electrolyte.
The PEM is relatively expensive at this point in time. We paid about $100 for a 30.5 centimeter by 30.5 centimeter (12 inch by 12 inch) piece of Nafion 117 from a chemical supply house. Some manufacturers want your first born child in exchange for a sample. However, du Pont really is in the PEM business, and they will sell it to you with no strings attached from their pilot plant production. The price comes down to about $65 for the same size piece when you buy four times as much PEM direct from du Pont. The piece we bought was large enough to make about six of our round fuel cells ($10–$16/cell).
Punching the PEM Disk from a Sheet of Nafion 117
We set the sheet of Nafion 117 on a piece of clean acrylic plastic using clean cotton gloves to avoid contaminating the sheet with fingerprints. Then we punched out some round PEM disks using a 4.76 centimeter (17⁄8 inch) arch punch and a mechanics hammer filled with lead powder. After one or two tries, we found that several strikes with the hammer at different angles was best for cutting the disk free from the sheet. Striking the punch too hard shattered the acrylic sheet.
Walt Pyle, Alan Spivak, Reynaldo Cortez, and Jim Healy
© 1993 Walt Pyle Agas fed battery that never needs
recharging! This article
describes a process for building a fuel cell using tools and techniques any skilled hobbyist with a well- equipped shop can duplicate. The fuel cell that we built can produce direct current electricity from stored hydrogen and oxygen. We obtained the hydrogen for this fuel cell commercially but plan to produce hydrogen and oxygen from a renewable energy system based on solar photovoltaics and water electrolyzers.
Cookbook Approach to Building a Fuel Cell
In this article we reveal the process we used to make a proton exchange membrane (PEM) fuel cell.
First, we describe what the PEM material is, and where to get it. Then we cover the steps necessary for preparing the membrane to use it in a fuel cell.
Next, we describe the catalyst and binders used on both sides of the PEM and the method of “hot- pressing” them all together to form the single fuel cell catalyst-PEM-catalyst “sandwich”.
Finally, the holder for the catalyzed PEM fuel cell with its gas supply piping, insulators, and wiring studs is shown.
Some PEM fuel cell performance data were obtained using an electrical resistor to provide a variable load. Two digital multimeters and a shunt resistor were used to measure the voltage and current, so we could calculate the power produced.
42 Home Power #35 • June / July 1993
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