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Author: Subject: Electrolysis cell design
Muzz1969
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[*] posted on 2-2-2015 at 19:10
Electrolysis cell design


I have been playing with basic cell constructions lately and want to get some input on things I need to consider when designing cells for high yeald low reaction time. I have a mechanical background with a full workshop at my disposal so can design and make any configuration.

Obviously surface area of anodes is a key to high yeald but what about spacing of electrodes? When we for example consider a bank of flat graphite anodes. How far apart would they need to be ?
Could they be stacked + - + - + - similar to a wet cell battery with say a 3mm gap between each anode.

[Edited on 3-2-2015 by Muzz1969]
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m1tanker78
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[*] posted on 2-2-2015 at 21:16


What are you electrolyzing and to what end? If, for example, you're reducing silver ions to metal, your plates need to be far enough apart that they won't short out with the metal dendrites. Another important general consideration is when your cell produces gas at one or both electrodes. Sometimes bubbles tend to cling to the electrode(s) or accumulate air pockets which increases localized current density on the parts that aren't covered in bubbles.



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Muzz1969
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[*] posted on 2-2-2015 at 21:59


Not anything in specific but firstly I'm playing with oxidation of primary alcohols
The unit I want to build will have a stirrer unit attatched so bubble formation shouldn't be an issue....As I build the unit I will post pictures. I am currently making the first unit with 10mm x 200 x 10 off round electrodes and I'm planning on a flat anode configuration for my second unit.

[Edited on 3-2-2015 by Muzz1969]
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macckone
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[*] posted on 3-2-2015 at 11:56


Planning an electrolysis cell without a clear goal is like
picking a vehicle for transportation without knowing
where it is going. Just getting on a random bus
isn't going to get you to Hawaii. I am pretty sure
you would need a plane or boat for that.

Figure out what you want to produce and then design
a cell. Your first goal seems to be oxidation of alcohols.
That means your cathode for the hydrogen generation
should probably be carbon as it won't catalyze a reverse
reaction. Your anode probably needs to be platinum or
something similarly catalytic. Using a divided cell will
help prevent your alcohol from being hydrogenated.

Spacing for this application needs to be lower than
electrodeposition. You may also need to encourage
flow around your electrodes. With a divided cell, that
means you need two pumps. And if you are using a
divided cell, you also need a membrane. Of which
there are many kinds for specific chemical applications.
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Muzz1969
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[*] posted on 3-2-2015 at 17:52


@macckone...ok well I'll start with the oxidation of primary alcohols.

So a few questions,

Why platinum? (I know it is a good non reactive material for anode use, but why use it over say a graphite anode)
Is the alcohol placed on one side of the membrane and the electrolyte on the other side of the membrane?
What type of membranes are there ? I can think of one such type that is used as separators in lead acid batteries. Are we looking for something that allows electrons to pass through but will not let the electrolyte and alcohol mix?
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macckone
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[*] posted on 3-2-2015 at 20:54


Platinum is just one possibility. It is an good multipurpose catalyst
Where as carbon is usually not catalytic.

Alcohol and a suitable conductive solvent is placed on one side
While an electrolyte solution is placed on the other.

There are a lot of membrane types. Nafion is one brand.
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Muzz1969
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[*] posted on 3-2-2015 at 21:01


With electrolyte choice , for example in the case of ethanol all the reactions I have read regarding this , they are mainly using dichromate, I have also read that these reactions can also be done in the presence of iodine or bromine. Would the elemental form need to be used or the salt form would be acceptable.

[Edited on 4-2-2015 by Muzz1969]
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macckone
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[*] posted on 3-2-2015 at 22:11


Dichromate is one of the catalyst I am familiar with.
No clue on bromine or iodine but I suspect the salt
Would be oxidized and that would oxidize the alcohol.
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pepsimax
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[*] posted on 3-2-2015 at 23:31


Quote: Originally posted by Muzz1969  
@macckone...ok well I'll start with the oxidation of primary alcohols.

So a few questions,

Why platinum? (I know it is a good non reactive material for anode use, but why use it over say a graphite anode)
Is the alcohol placed on one side of the membrane and the electrolyte on the other side of the membrane?
What type of membranes are there ? I can think of one such type that is used as separators in lead acid batteries. Are we looking for something that allows electrons to pass through but will not let the electrolyte and alcohol mix?


Graphite is messy, i'd use an anode bag for it. In my experience (mainly plating, never done any proper electrochemistry) it can easily flake off tiny carbon particles. An anode bag can easily be had by searching for a 10 micron diesel filter bag on ebay or amazon.
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Muzz1969
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[*] posted on 8-2-2015 at 02:07



Ok, so I have built a test cell with a PTFE divider. I am using graphite for both rods to start with. I have used filter paper as the salt bridge between the two cells.

I have place ethanol + water in one cell and sodium dichromate + water in the other cell

The cell is drawing 200mA @ 12 v

The Ethanol is bubbling away with the dichromate appearing static

Can anyone tell me if this is correct in the way I have set it up.
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[*] posted on 8-2-2015 at 05:01


Try this video.



When the police come


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Muzz1969
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[*] posted on 8-2-2015 at 05:15


@chemkid....sorry but what does making hydrogen have to do redox reaction of ethanol
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