Sciencemadness Discussion Board

DIY Divided electrochemical cell with stirring and cooling

bearbot22 - 20-6-2022 at 11:00

I'm proud to present the design of an Electro-Chemical cell that has been developed and improved over a long period of time, with the aim of developing a DIY electrolysis cell that is reliable, features membrane aka diaphragm, stirrer and cooling but also is made from inexpensive and readily available parts.

Blueprint with parts list of the cell can be found in the attached file.

Wondering what to make with such a cell? Well - a lot of chemicals. Take a look in sciencemadness' Library: The Manufacture of Chemicals by Electrolysis

What follows now is a rather long "making of"- text with some hopefully useful information for anyone who wants to design or improve an electrolysis cell.

I started with a beaker-type cell because i had a beaker in my collection. On top of the beaker I put a plastic lid into which I drilled slots and holes for electrodes.

On the Internet i found a tutorial for a DIY magnetic stirrer made from an old PC: Magnets taken from a HDD glued to a CPU fan and connected to the PC power supply, and a sandwich box as enclosure. This magnetic stirrer worked really well and for a long time and the PC's power supply also provided 5V and 12V DC for electrolysis. Of course, I still needed a magnetic bar for the stirrer. I made some out of screws and nuts, wrapped with tape or shrink tubing or plastic tubes with magnets in them. But because they didn't last and weren't balanced well, I quickly opted for PTFE magnetic stirring bars.

To measure the current, I got a cheap digital multimeter from the hardware store.

Next i went for an an more flexible power supply, which I built from the transformer of an IKEA halogen lamp and an electronic adjustable AC/DC module. So I was able to adjust voltage and read the flowing current on the multimeter.

Membrane aka diaphragm was a tricky part. I tried many things: Sheep casings and gelatine ... they decomposed. A salt bridge hadn't allowed enough current to flow.
Gore-Tex, composable plastic film and Fimo haven't allowed electricity to pass at all, nor have porcelain vessels with scraped glaze, unglazed porcelain or most commercially available flower pots.

AFAIK Ceramics are fired twice to make em firm an waterproof. Suitable as a membranes, are ceramics that are fired only once such as Terracotta or Blumat water dispensers for flowers. But their thick walls allow only little current to flow.

The clay tubes i found are sold in aquarium shops in stacks of six as breeding shelter for shrimp. You 'll need to scrape the tubes off the stack and also have to grind the glazing off in- and outside. This can be done with a rough round file and a sharp screwdriver.
Similar caves are also offered with a closed bottom, but I haven't found a way to remove the inner glaze without breaking it.

If someone has the opportunity to build a test tube-shape porous ceramics that is fired only once, that would certainly be a pretty cool improvement.

Using the shrimp clay tube i needed to seal the bottom, which is not as easy as i assumed. Stuck a plastic shopping cart chip to it but no glue I know kept it. So I tried tape, stoppers, etc... nothing lasted. Even a long screw made out of nylon which i stuck through the tube to hold the bottom decomposed. It seems that during electrolysis, the inside of an anode cell turns into a corrosive hell. That's why I came up with a bracket of cable ties.

The level of anode electrolyte should be higher than the electrolyte level in the cell. I think this way osmotic pressure prevents redox reactions.

As a supposed further improvement, I bought an quite expensive fuel cell membrane. Building an anode cell for this membrane was complex because seals were needed and had to hold together with a lot of screws. This finally worked but did not allow more current to flow than the clay tube did. After the first electrolysis the (dry) membrane broke mechanically. So I decided to stick to the clay tube.

Nafion? I didn't test this. IMHO it's too expensive and difficult to obtain for a DIY cell.

For cooling, I had a double-walled vessel in mind from the beginning. First I put the beaker in a plastic cup to which I hot-glued tubes for inlet and return. I put a pot with diluted antifreeze and a small pump in a freezer (drilled holes in the Cover for tubing and power supply).
Since the beaker could move inside the cup, the stirring bar smeared off quickly or if the inlet or outlet were not properly free, it cooled too little or flooded the beaker so this was not particularly reliable.

Using a cylindrical 'Lock-n-Lock' container, I was able to built a much more reliable double-walled vessel. Cut a suitable hole in the plastic lid, place the beaker in it and fixed it waterproof with hot glue.

When electrolysis ran for several hours or even days, a lot of condensation water formed and finally the magnetic stirrer stood in a puddle. So I put the beaker and magnetic stirrer rihgt inside the freezer. This turned out to be a good idea and I did a lot of electrolysis successfull with this setup.
Since there already were holes in the freezer's cover, any hydrogen gas could escape.

Temperature control was done by adjusting the freezer, which was not very accurate. So I ordered a cheap 'STC1000' controller on the Internet. With this, i had the pump and freezer run only when cooling was needed.

However, the handling of the cell was still a bit fiddly, firstly because the plate with the electrical connections wasn't really fixed to the beaker and secondly the Lock'n'Lock vessel could slip on the magnetic stirrer and thus cause the stirrer to fail.

That's why I redesigned an electrolytic cell with everything fastened to a screw-on cap. For this I replaced the beaker with a cylindrical glass jar with a screw cap made of plastic and found a suitable one in a local shop with 500g of honey in it. This is the reason why I call the cell's design "Honeypot".

Maybe Honey is sold in these jars only where i live so you might look for a cylindrical glass jar with plastic screw cap filled with peanut-butter, marshmallow spread or whatever.

Cut out the lid and screwed on a sturdy disc made of acrylic glass to which stirring-motor, cathode, anode-cell and temperature sensor are attached. The attached drawing shows how its done exactly.

As a stirring drive, I initially used a cheap DIY Robotics motor with plastic gearbox, but unfortunately those fail after a few hours of continuous operation. A 20D 6V DC motor with metal gearbox plus a USB power supply seems to be much better.

As a power supply for electrolysis, I replaced the IKEA-Transformator+Multimeter- Thing with an adjustable lab power supply (2A/30W) because its short-circuit-proof and less wiring is needed.

For cooling I use a fridge with icebox. I unscrew the top cover and cut a circular hole in the insulation so i can put the cell right inside the icebox. After reassembling, this modification of the Fridge is barely visible. During electrolysis, Fridge is set to max cooling and powered via the STC-1000 controller. A soft cooling pad under the glass jar improves heat dissipation.

Hope this gets your lab a little further - BearBot22
Attachment: honeypot3.pdf (75kB)
This file has been downloaded 72 times

mysteriusbhoice - 27-6-2022 at 10:43

use ionomer cement if you want a cheap good membrane
cement and cation/anion exchange resin commonly sold in water filter store cement to ionomer cement wt ratio 1:3
you can also use plaster of paris if instead of cation exchange resin.

this mixture is mixed with water and casted across a glass container with 2 dividing walls which will produce a dam (membrane) which is highly conductive due to the imbedded ion exchange resin or plaster of paris CaSO4 which can also exchange ions.

bearbot22 - 18-7-2022 at 05:16

hi mysteriusbhoice,

the electrolyte used is 7-10% H2SO4 in water/alcohol - i'm not really sure plaster of paris aka gipsum will last.
also i read cement becomes instable when in contact with gipsum before it is totally dry.

i've never heard of ionomer cement before, so i'll give this a try.

mysteriusbhoice - 18-7-2022 at 17:23

Quote: Originally posted by bearbot22  
hi mysteriusbhoice,

the electrolyte used is 7-10% H2SO4 in water/alcohol - i'm not really sure plaster of paris aka gipsum will last.
also i read cement becomes instable when in contact with gipsum before it is totally dry.

i've never heard of ionomer cement before, so i'll give this a try.



Gypsum will last with H2SO4 as I've used it in up to 20% without issues but it will be attacked by NaOH.
Also the gypsum and cement being unstable only matters for construction applications and this membrane won't bear any load and they seem rock solid.
Anyway cation exchange resin with cement is good too and use glass container not plastic because plastic will flex.

mysteriusbhoice - 19-7-2022 at 02:23

I have a video on my channel about making various ion exchange membranes and the ionomer cement is convenient and allows for a membrane which is both not as porous but highly conductive to the particular ions of choice depending on the resin you choose.
The current flow is shown in my video and it's quite decent compared to terracotta which only really did decent past 12 volts.