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PEM Fuel Cell

PostPosted: Thu Jan 29, 2015 8:49 pm
by Peter Schmelcher
Almost two years ago I did some experiments with a Proton Exchange Membrane or PEM fuel cell. Only a few companies actually make these membranes. This fuel cell came out of a science toy called a Hydrocar. The highest current I ran the cell at was 4.5 Amps while producing 36 sccm of hydrogen gas. In the video you are looking at the water and oxygen gas side. To reduce internal resistance the PEM is in contact with a diamond shaped metal mesh that is unfortunately not stainless steel but probably aluminum. I have seen other fuel cell that use a perforated SS foil which I prefer. The syringe is used to circulate and separate the O2 and water which keeps the membrane wet.


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Re: PEM Fuel Cell

PostPosted: Mon Feb 02, 2015 1:12 pm
by Doug Coulter
I can see this being useful for those who can't get pure D for their fusors, but can get heavy water. Of course, drying out the resulting gas is quite difficult - the regular methods don't get it below about 1% or so water in the gas, and heavy water (for whatever reason) tends to dilute itself with regular water from the air quite rapidly in our tests here...but it's a worthwhile thing if someone gets the whole system going for certain, as pure D in tanks is neither cheap nor these days, easy to get at all.
Glad I got a big tank.

We did purity tests here, and at around 1/2% water - behavior in a fusor is very different. It's more stable than with pure to 4-5 9's purity, but puts out lots fewer neutrons, all else being equal.
Dririte, P2O5, pure sulfuric, dry ice - will not get you under .5% dry.

Of course, there are plenty of other uses for this - microflame welders (have one) don't seem to mind a little water in the gas at all, for example.

Re: PEM Fuel Cell

PostPosted: Tue Feb 03, 2015 11:34 pm
by Peter Schmelcher
I looked at all the usual suspects for drying awhile back. Some might be fine but probably not great and I did not want to invest in an RGA to know the answer. I liked zeolite as the drying medium and I eventually found a few commercial drying products with specifications that used it.

Zeolites are an interesting filter media. I have a 5liter/minute oxygen machine that concentrates O2 to about 95% from room air using zeolites. I did glass blowing when I was younger and O2 in a welding bottle is inconvenient and hard on the wallet.

For filtering water vapor from deuterium a 4 or 5 Angstrom zeolite is used.
According to manufacturers like HP this results in 200ppb residual moisture content. Actually some report 500ppb but this might be the end of life replace the filter number. You can go further down to about 5ppb with a mostly one way chemical reaction. They use a high surface area of a metal that desperately wants to become an oxide. Anyway, these are all off the shelf parts for a gas chromatography machine. Just hook them up and you’re done.

Re: PEM Fuel Cell

PostPosted: Fri Feb 06, 2015 1:40 pm
by Doug Coulter
Well, I tried all that and I DO have a mass spectrometer. Tons of water makes it through ( a few percent ), and worse, plain old hydrogen from heavy water contamination from the vent you have to have for the oxygen to get out. The stuff seems to attract plain water like a magnet. In theory, practice is the same as theory, in practice, it's another story. I gave up and just bought deuterium.