PEM electrolysis example

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Rex Allers
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PEM electrolysis example

Post by Rex Allers »

Recently there's been discussion (again) about electrolysis for getting deuterium from deuterium oxide (or heavy water).

I have done one a while ago but never posted about it because I felt it incomplete. To complete it, I feel it should have a drier section, some kind of interum gas storage, a metering valve or control system. And I think nice, small-volume plumbing will be a good goal.

Introduction to Electrolysis
The traditional approach is to have two electrodes in a chamber of water with a voltage applied between them. The electric energy splits the atoms of the water molecules and attracts
the hydrogen to
the negative electrode (cathode)
and the oxygen to the
positive electrode (anode).

This forms bubbles of the two gasses on their respective electrodes. By putting tubes or some other enclosure around each of the electrodes while keeping a liquid path between them to allow electric current to flow, the two gasses can be accumulated in their two chambers or tubes.

PEM Cell
A more recent approach is the PEM cell (Proton-exchange membrane). The main focus for using these cells is to take hydrogen and oxygen gas as fuels and put them into opposite sides of a PEM membrane to create water and extract energy from the reaction as a voltage on two electrodes on opposite sides of the membrane.

These cells and membranes can also be used in the opposite mode, where water is applied on the positive side and a voltage is applied to the cell membrane sides. The water is split and the O2 is released on the water side (+). The hydrogen from the split molecules migrates through the membrane and is released on the (-) side into a typically non-liquid space.

This is a very brief and simplistic explanation.

Advantages of PEM Cells
----
Advantages of using a PEM cell for electrolysis (with focus on D2O) vs
standard method (2 electrodes in liquid with isolation of the 2 molecular gas streams)
  • No ionizer (acid or salt) needs to mixed in the water/D2O
  • Liquid is only on the O2 side of the membrane. Keeps H2 or D2 much drier than standard method where H/D bubbles through the liquid.
  • The volume of liquid needed in the cell is very small. Nice for not wasting costly D2O.
  • Not usually employed, but the H/D side can generate some positive pressure.
----

To use these methods for a fusor, the water is replaced with deuterium oxide (or heavy water) where the hydrogen is now a hydrogen isotope deuterium which has a neutron that the normal hydrogen atom does not have. The electrolysis works the same way producing oxygen at the positive electrode but now the gas at the negative electrode is deuterium.

Small versions of these PEM cells have been available for several years, most intended to demonstrate the fuel cell, where hydrogen and oxygen are combined to produce water and electricity. They can be reversed to do electrolysis with water injected and voltage applied to split the water into H2 nd O2.

--- Note in 2021, the following links don't seem to still be a valid source for the small cells ---
--- I will look up vendors that work in 2021 if I move this post to a more permanent location
than New User Chat ---

One vendor that sells these small cells is:
the FuelCellStore
https://www.fuelcellstore.com

They seem to sell products made by:
Horizon Fuel Cell Technologies
https://www.horizonfuelcell.com

although I can't seem to find these smaller devices mentioned on the Horizon pages.

--------------------
My Implementation

So, a few years back I made a setup using a PEM cell to make deuterium for a fusor. So far, I haven't tried with anything but regular water. I have some deuterium oxide (heavy water) when I am ready. I haven't shared this because I feel just this far on a deuterium source is incomplete. Things I plan to add are a drier for the gas, a small storage chamber and a metering valve or system to regulate the flow into a fusor vacuum.

But the additions I made around the cell seemed in testing to be working well and produced hydrogen from water. As I said D2O not tried as no reason to waste it at this stage.

A fuel cell from one of those old plastic car demos would have probably worked, but I used one actually intended as an electrolyser. Here:
Horizon Mini PEM Electrolyzer
--- 2021 - need working vendor ---
https://www.fuelcellstore.com/horizon-m ... s-fcsu-010

So, got the cell.
Goals
Need to make a way to inject water or D2O. Need to capture H2 or D2. Need to let out or usually vent O2. Need to seal unused ports. Need to feed electricity to the electrodes.

With the cell standing on edge, the (+) positive side gets a tube for liquid input on the bottom port. The top port is to vent the O2 output.

The (-) negative side provides the H2 or D2 output from the top port. The bottom port is unused and blocked off.

My Device
Pretty simple connections, from above. but lets think about details.

Here's a picture of the H2 side of the cell. The other O2 side looks the same.
Cell side.jpg
and another view
Cell top.jpg
The H2 side is simple. Take the H2 or D2 output from the top nipple port. Block off the bottom port.

On the O2 side it is more complicated, as this is where the liquid needs to fill. The simplistic view is liquid comes in on the bottom port and O2 comes out on the top port.

Here's a view of what I created.
My rig 1.jpg
The two largish tubes are made from plastic syringes. (they are cheap and availble on ebay)

The rightmost one is the reservoir that fills the liquid into the O2 side. Making this a bit large lets the O2 side stay full or nearly full as it converts small amounts of liquid to gas. Without this reservior the O2 chamber would deplete faster and have less of the electrode area submerged.

Here's another view.
My rig 2.jpg
The leftmost syringe piece is on the O2 output (top port). In actual experience running this device, this top port has bubbles tending to lift out with the O2 gas. This small syringe gives a place for the bubbles to break and the liquid flow back into the chamber.

The tops of both syringe pieces are capped with filters. These are vinyl tubes that fit closely into the syringe tops, but also have a cotton-like fiber to fill the opening. On the O2 side this is the vent. On both sides it is a filter for contamination. This plug, on the right liquid side, can be removed to inject or adjust the liquid for electrolysis.

For feeding electricity into this converter, I think the gas output should be proportional to the current into the device. (amps) So I made a simple adjustable current source from an LM317 chip and appropriate circuit. For most apps this current source is probably overkill and some adjustable specifed voltage source is probably stable enough.
Rex Allers
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Rich Feldman
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Re: PEM electrolysis example

Post by Rich Feldman »

Thanks for sharing, Rex. Are you going to run it with regular water before switching to D2O?

Looking forward to seeing quantitative results, including 1) amount of gas per coulomb and 2) amount of water in the gas.

Here's a link to old thread that includes Bob Reite's heavy water electrolyzer, and my unreviewed calculation of the coulometric constant: 143 mA per sccm of hydrogen. viewtopic.php?f=6&t=9956&p=67075
All models are wrong; some models are useful. -- George Box
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Richard Hull
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Re: PEM electrolysis example

Post by Richard Hull »

Rex, Please do us all a favor and copy your main post as a FAQ in the FAQ section of the Construction or Vacuum forum or both. It is very informative. It needs to be a FAQ. The title can be some thing all inclusive like "FAQ - Deuterium gas from a PEM cell".

I have yet to understand why more folks don't do FAQs, when they give a rather complete explanation of a process that is relevant and often brought up. FAQs are not my domain but that of anyone who can take a subject and give a relatively complete explanation and procedural path on a topic yet to be fully treated in another FAQ.

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
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Bob Reite
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Re: PEM electrolysis example

Post by Bob Reite »

I would advise NOT using ordinary water in a cell that you plan to use for heavy water later, else your D2 will be contaminated with H2 for I don't know how long. One should also install an over/under pressure system as the membrane can be damaged, if say something goes wrong with the mass flow controller or misadjustment of the needle valve in your setup.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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