PEM Cell Question

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Alexey Khrushchev
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PEM Cell Question

Post by Alexey Khrushchev »

Hi!
I bought a cheap PEM cell ($25) to get deuterium from heavy water. I filled it with high purity water with a resistance of 18 megohms for testing. I applied a voltage of 2.8V using a regulated power supply. The current was about 2A at first and hydrogen was being produced quite vigorously. But after 5-10 minutes the current started to decrease and dropped to 0.2 A. Hydrogen continued to be released but very slowly, the total rate was 60 ml in 40 minutes. Is it possible that my cell is damaged?
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Jim Kovalchick
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Re: PEM Cell Question

Post by Jim Kovalchick »

Did you maintain constant liquid level in the cell throughout your test?
Alexey Khrushchev
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Re: PEM Cell Question

Post by Alexey Khrushchev »

No, I poured about 0.5ml of water into the cell and applied voltage. After the test, the water level dropped slightly, about 5-7 mm.
Rich Gorski
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Re: PEM Cell Question

Post by Rich Gorski »

Alexey,

As Jim indicated it sounds like the PEM cell went dry. I see the same drop in current in my PEM cell if I don't maintain liquid circulating through. Sounds like the cell just needs to be refilled. I use about 2mL of water and keep it circulating through the cell with a small pump. 2mL will last about 2 to 3 hours before it dries up and the current drops.

Rich G.
Alexey Khrushchev
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Re: PEM Cell Question

Post by Alexey Khrushchev »

It takes about 0.05 mL of water to produce 60 mL of hydrogen. So only 10% of the original volume was used up. Why do you write that the cell is dry? Or am I misunderstanding something? I repeated the experiment today, again the current dropped to 300 mA rather quickly. I tried pumping water during electrolysis with a syringe, but this did not increase the current. I had a crazy idea about that. Maybe I am using too pure water with a very high resistance. It is obtained from a lab facility for ultra pure water. Perhaps in the first few minutes of electrolysis the carbon dioxide dissolved in the water acts as an electrolyte and increases the conductivity of the water, but then as it is removed the resistance becomes too high for effective electrolysis.
Rich Gorski
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Re: PEM Cell Question

Post by Rich Gorski »

Dry meaning not enough fluid to properly wet the membrane (not really dry). When active my cell draws about 1A current at 4V which implies a "resistance" of 4 ohms. Of course the water does not have 4 ohms resistance its the splitting of the water molecule into +H ions and -electrons that is the current we measure. The water resistance you mentioned of 18Mohms (typical of distilled water I assume) is not a problem for a PEM cell membrane. The loss of water happens I believe mostly through evaporation on the O2 side of the cell since this side is generally open to air. There is also some amount of water vapor that shows up on the H2 side. As I mentioned my PEM cell loses about 1 or 2 ml within about 2 hours of operation and has to be refilled. In your case since you did refill it without success I assume your PEM cell is not functioning properly.
Alexey Khrushchev
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Re: PEM Cell Question

Post by Alexey Khrushchev »

Thanks Rich. I think you are right and my cheap cell is faulty..... There was a similar problem mentioned on this forum a few years ago. I also noticed that the cell on the hydrogen side gets covered with condensation during electrolysis. This means that the gas comes out very wet and needs to be dried. The miser pays twice... I have never run the cell at voltages above 4V, I will have to try it, it should increase the hydrogen flow.
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Richard Hull
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Re: PEM Cell Question

Post by Richard Hull »

I assume you have seen the 3 fabulous videos concerning the PEM cell's operational use in the FAQ. These are among the finest and most complete involving the fuel cell with many operational intricacies explained. Mark Rowley gave all PEM cell users a true gem here.

viewtopic.php?t=13995

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Alexey Khrushchev
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Re: PEM Cell Question

Post by Alexey Khrushchev »

Of course! I scrutinised the video and the forum topic. I plan to use a tube filled with calcium metal powder to dry the hydrogen. Hopefully this will maximise the conversion of all the heavy water to deuterium.
Peter Schmelcher
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Re: PEM Cell Question

Post by Peter Schmelcher »

The PEM cell is at best 50% efficient and probably closer to 35%. So, 65% of the energy heats the water creating a need to cool the D2O using circulation, or alternately use a very low current so the D2O remains close to room temperature. For circulation the rising O2 bubbles can create D2O flow into a reservoir for cooling and gas separation.
Picture 241.jpg
Links to a 5 second video of my PEM cell running at 1.5 and 4.5A. The cell edge is at 45degrees to the vertical so the inlet hole is the lowest point and the exhaust hole is at the highest point.
https://www.youtube.com/watch?v=huiVgMdcNXQ
https://www.youtube.com/watch?v=9DKmkQrZ9Rs

-Peter
Alexey Khrushchev
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Re: PEM Cell Question

Post by Alexey Khrushchev »

It looks like a circulating pump is a good solution to remove oxygen and cool the cell. At what rate are you running water through the cell? Are you using a deuterium dehydrator?
Peter Schmelcher
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Re: PEM Cell Question

Post by Peter Schmelcher »

The bubbles create sufficient flow but the cc/minute is unknown. On the deuterium side a small amount of moisture exists so condensing using cooling is followed by a Supelco moisture filter.
-Peter
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