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I am separating water into hydrogen and oxygen via electrolysis.

The electrolyte solution is sodium hydroxide (NaOH) in deionized water.

Electrodes are 99.96% pure nickel.

All gases and liquids are perfectly clear. Even after running for hours, the electrolyte solution is crystal clear and colorless.

However, the reaction seems to be emitting something that burns the nose and throat of everyone in the room.

Is that some sort of gas from a side reaction at one of the electrodes, or is it simply bits of NaOH being carried into the air by the splashing bubbles?

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  • $\begingroup$ What is the NaOH concentration of your solution? $\endgroup$
    – airhuff
    Commented Aug 7, 2017 at 0:50
  • $\begingroup$ I used about 250 grams, in 6-8 litres of water, so maybe 4-5% ? $\endgroup$
    – MadScientist
    Commented Aug 7, 2017 at 0:52
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    $\begingroup$ I think your guess of the NaOH forming aerosols from the bubbling is pretty likely. I don't know what your apparatus looks like, but it may be that just covering it, or the bubbling portion of it, could resolve your problem. Of course protect your eyes when working with this solution (I don't know your level of chemistry training either, so have to mention it ;). Maybe someone will come up with something else, but I suspect that is it. $\endgroup$
    – airhuff
    Commented Aug 7, 2017 at 1:06
  • $\begingroup$ @MadScientist. From your description it smells like Ozone. Perhaps you are at some overpotential. $\endgroup$
    – Alchimista
    Commented Aug 11, 2017 at 14:21

2 Answers 2

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TL;DR: Your suggestion that the problem is "simply bits of $\ce{NaOH}$ being carried into the air by the splashing bubbles" is very likely correct.

You have a very simple system, meaning a minimal number of variables to consider in order to eliminate other possibilities. For example, if you were using $\ce{NaCl}$ as the electrolyte, then chlorine gas could be the irritant. But with $\ce{NaOH}$ as the electrolyte there really is no side reaction that could produce such an irritant.

On the other hand, $\ce{NaOH}$ itself can irritate sensitive tissues like mucous membranes, and even skin for that matter. According to one of your comments, you are using a $\ce{NaOH}$ strength of a bit over 1 molar. Droplets of this solution will eventually be neutralized by $\ce{CO2}$ in the air, but at that strength it should stay around long enough to elicit the symptoms you described.

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  • $\begingroup$ Thanks for that. Can these aerosol droplets be filtered using something like glass wool? I'm pumping out the hydrogen and don't want to contaminate the output with NaOH. $\endgroup$
    – MadScientist
    Commented Aug 8, 2017 at 2:46
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    $\begingroup$ It's hard to say what would work best without knowing what your apparatus looks like. You can probably just cover the area where the bubbles are coming out of solution with a plastic lid just over the surface. No need to be air-tight or anything, you just need to stop the splattering from freely going into the air. Again, not having seen your apparatus, that's kind of a shot in the dark answer. $\endgroup$
    – airhuff
    Commented Aug 8, 2017 at 4:31
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Dependending on the potential you apply, side reactions occur. One taking place at moderate overpotential is O2 + 2 OH- giving O3 + H2O and 2 electrons. . Considering the above in conjunction with

  • the alcaline pH you are working with,

  • that the "smell" spread to the room in spite of CO2 neutralising the hypothetical NaOH droplets

I really think that what irritates your nose is O3.

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  • $\begingroup$ Thanks for that. Any idea how what voltage/pH I can have in order to prevent this? $\endgroup$
    – MadScientist
    Commented Aug 11, 2017 at 20:17
  • $\begingroup$ I think it might be easy and safer to work with NaCl but it is also easy to get Cl2. Why you do not try some sulphate, e.g. Na2SO4? Moreover try to control the potential, just enough to keep your stuff bubbling. $\endgroup$
    – Alchimista
    Commented Aug 11, 2017 at 23:17
  • $\begingroup$ You should get water electrolysis with about 1.5 V. The point is that overpotential (for water splitting as well as for secondary reactions) will depend on your specific setup. Are you demonstrating or somehow producing? :) $\endgroup$
    – Alchimista
    Commented Aug 11, 2017 at 23:24
  • $\begingroup$ It's not for demonstrating purposes, I'm producing H2 at a large scale (inflating large lighter-than-air aircraft), and I produce much more with higher voltages. (Yes, I know, Hindenberg..) $\endgroup$
    – MadScientist
    Commented Aug 12, 2017 at 7:59
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    $\begingroup$ Then it is your source. You need current rather than voltage. Is really matter of setup. Anyway give a try to sodium sulphate $\endgroup$
    – Alchimista
    Commented Aug 12, 2017 at 12:11

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