Safe electrolytes for electrolysis.

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Himself
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Safe electrolytes for electrolysis.

Postby Himself » Tue Apr 18, 2017 1:19 am UTC

I am interested in producing hydrogen gas but I would like to minimize the hazardous materials I would have to deal with. My main concern is what electrolyte I could use without having to worry about hazardous byproducts.
Sodium chloride is out because, as I understand, it would likely yield some chlorine gas. For obvious reasons I don't want to use any strong acids or bases, though some hydrogen generators use sodium hydroxide.
My first choice at this point would be magnesium sulfate as it is easy to obtain, but would hope to get some information from someone with a better understanding of electrochemistry.
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Re: Safe electrolytes for electrolysis.

Postby p1t1o » Tue Apr 18, 2017 2:07 pm UTC

You can just use distilled water, electrolytes just reduce the energy requirement which for small scale projects, isn't exactly prohibitive.

You also want to find some graphite electrodes, if you are using metallic ones, you are likely to get weird "gunge" that is the bain of the amateur electrochemist. (basically your electrodes dissolve and form a mixture of various salts)

Sodium hydroxide isnt too dangerous if you acquire it in the form of dilute solution, and it doesnt need to be very strong at all to be used as an electrolyte. The only problem is impurities, as only small amounts can result in the aforementioned "gunge".

Obviously, nobody can give you advice on this topic without also reminding you that hydrogen is a flammable, explosive gas that is also invisible and burns with an invisible flame. If you are planning on producing more than a sort-of-handful-sized-amount-if-you-use-your-imagination of hydrogen things start to get more dangerous. But small scale desktop electrolysis is fairly benign.

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Re: Safe electrolytes for electrolysis.

Postby Himself » Wed Apr 19, 2017 3:42 am UTC

So would common batteries in distilled provide enough voltage for distilled water without being painstakingly slow?
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Re: Safe electrolytes for electrolysis.

Postby WibblyWobbly » Wed Apr 19, 2017 4:15 am UTC

You ruled out sodium chloride because of the possibility of chlorine-generating side reactions, but what about something like sodium bicarbonate? A sodium salt would still be a good idea if you're interested in making the electrolysis easier, and as far as I know, sodium bicarb isn't going to be caustic (as sodium hydroxide) or release chlorine.

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Re: Safe electrolytes for electrolysis.

Postby p1t1o » Wed Apr 19, 2017 8:46 am UTC

Himself wrote:So would common batteries in distilled provide enough voltage for distilled water without being painstakingly slow?


Depends on the number and type of battery, naturally. A single 1.5V AA battery will obvs be quite slow, but the reaction should progress.

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Re: Safe electrolytes for electrolysis.

Postby Himself » Wed Apr 19, 2017 1:33 pm UTC

I was thinking of wiring up parallel batteries anyway. I had thought of using sodium bicarbonate as well, but I am wasn't sure if I might get adverse reactions from the anion such as reduction to CO or something like that, though that might not be a problem if the area is well ventilated.
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Re: Safe electrolytes for electrolysis.

Postby WibblyWobbly » Wed Apr 19, 2017 1:55 pm UTC

Himself wrote:I was thinking of wiring up parallel batteries anyway. I had thought of using sodium bicarbonate as well, but I am wasn't sure if I might get adverse reactions from the anion such as reduction to CO or something like that, though that might not be a problem if the area is well ventilated.

I'm fairly certain the reaction should proceed to carbon dioxide, not monoxide, if anything, but as you say, for a relatively small scale electrolysis, a well ventilated area should be sufficient. Also, don't huff your products.

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Re: Safe electrolytes for electrolysis.

Postby p1t1o » Wed Apr 19, 2017 3:03 pm UTC

You definitely wont get CO by electrolysing bicarb 8-)

However, Im not sure if it is a suitable electrolyte, if its electrode potential is too high, it will outcompete the production of hydrogen and you will just get carbonated sodium hydroxide solution.

Yes, on checking, bicarbonate is not an *ideal* electrolyte, but it will work. You will still make hydrogen and oxygen, but there will also be a proportion of CO2 produced as well, although for the life of me I cannot remember how to figure out which electrode the CO2 appears at, am a little rusty, on my piece of paper here I have electrons flying about all over the place.

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Re: Safe electrolytes for electrolysis.

Postby Himself » Wed Apr 19, 2017 5:20 pm UTC

I expect the CO2 would form around the anode.
2H2O --> O2 + 4H+ + 4e-
So the pH around the anode would drop.

What of magnesium sulfate, then? It could release SO2 or form small amounts of sulfuric acid or magnesium bisulfate I imagine.
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Re: Safe electrolytes for electrolysis.

Postby p1t1o » Thu Apr 20, 2017 8:32 am UTC

Himself wrote:I expect the CO2 would form around the anode.
2H2O --> O2 + 4H+ + 4e-
So the pH around the anode would drop.

What of magnesium sulfate, then? It could release SO2 or form small amounts of sulfuric acid or magnesium bisulfate I imagine.


I think that sulfate is safe, unlikely to strip two oxygens off it and produce sulphur dioxide, you cant just rearrange the atoms in any combination. By all reports Magnesium sulphate is a reasonable choice, but electrolysis would involve species of Magnesium Hydroxide and Sulphuric acid I think, so the pH at your electrodes may not be neutral, so take appropriate precautions eg: lab goggles.

To be honest though, one should be in gloves, labcoat/apron and goggles even if you were just working with totally benign reagents in any scientific/experimental context. Which will protect you from most things you can do with household batteries and cupboard reagents.

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Re: Safe electrolytes for electrolysis.

Postby Himself » Thu Apr 20, 2017 1:42 pm UTC

I wasn't sure about SO2. I had read somewhere that sulfuric acid was commonly made by oxidizing SO2 to SO3 , so I guess I was concerned about that reversing.

I'm not concerned about magnesium hydroxide considering it is used as an over the counter antacid. I was even considering using it as a buffer to lower my chances of getting unwanted acids.
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Re: Safe electrolytes for electrolysis.

Postby p1t1o » Thu Apr 20, 2017 2:48 pm UTC

Himself wrote:I wasn't sure about SO2. I had read somewhere that sulfuric acid was commonly made by oxidizing SO2 to SO3 , so I guess I was concerned about that reversing.

I'm not concerned about magnesium hydroxide considering it is used as an over the counter antacid. I was even considering using it as a buffer to lower my chances of getting unwanted acids.


Yes, at this scale, you are not going to generate very extreme pHs easily, but its always best to take precautions, even a very dilute solution will be very irritating to your eyes, even if it not strong enough to burn. And there is always an outside chance of some random combination of errors and happenstance that could generate something unexpected.

Magnesium hydroxide on its own would actually make a decent electrolyte, the same as sodium hydroxide. Actually I would go for the hydroxide over the sulphate - why worry about what a sulfate ion is going to do when you can substitute hydroxide which will be present as either a nice hydroxide charge carrier, or water.

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Re: Safe electrolytes for electrolysis.

Postby Himself » Thu Apr 20, 2017 2:57 pm UTC

Even given the low solubility of magnesium hydroxide? Though I see the appeal of limiting what anions are present.
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Re: Safe electrolytes for electrolysis.

Postby p1t1o » Thu Apr 20, 2017 4:10 pm UTC

Himself wrote:Even given the low solubility of magnesium hydroxide? Though I see the appeal of limiting what anions are present.


You shouldn't need a very high concentration to have a significant effect, but you can always use sodium hydroxide. Goggles, gloves and a water tap nearby to rinse any splashes off and safety shouldnt be a problem.

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Re: Safe electrolytes for electrolysis.

Postby Himself » Fri Apr 21, 2017 1:57 pm UTC

I'll try the magnesium hydroxide and see how that works.
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