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We are designing a small electrolyzer (about 1 kW input power) for HHO gas generation. Sadly most of the literature online is bordering on the snake oil… However, it works fine with DC driving. Now from the electrical side the cell is a quite complex model (the current–voltage curve depends on anything under the sun) and we want to give a way to regulate the amount of gas produced. The idea would be some kind of PWM.

I found an article by Mazloomi et al. [1] (there are some thing inside I'm not very convinced of, first of all the circuit model) but the current transient matches what we see:

  • An initial peak (the electrolyzer plates charging as capacitor?)
  • An exponential rise (the actual electrochemistry starting up?)

My guess it that the minimum frequency for a PWM drive would be such that at least the current transient completes. But I also read that the gas formation processes are somewhat slow, due to bubble mechanics.

The question is: is there a recommended frequency for driving such an electrolyzer cell? I am thinking about three possible outcomes:

  • Ultra low frequency, like turning on 10 s the generator and let it idle 2s;
  • Low frequency, around 100 to 1000 Hz, where the transient completes (electrically) but I don't have a reasonably good idea of what's happening on the chemistry side;
  • High frequency (kHz range) where the electrical inductance in practice becomes a (lower) constant current and the generator is substantially at a DC steady state.

The first way is easy to do but the discontinuity in generation is problematic; the third way gives substantial thermal stress on the electronics due to switching losses. The middle way seems a good compromise to me. Are there some guidelines? Any kind of pointer can be useful.

Reference

  1. Mazloomi, K.; Sulaiman, N.; Ahmad, S.; Md Yunus, N. Analysis of the Frequency Response of a Water Electrolysis Cell. Int. J. Electrochem. Sci 2013, 8. (PDF)
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    $\begingroup$ Why do you want to produce electrolysis with pulses ? is there any advantage ? $\endgroup$
    – Maurice
    Mar 28, 2022 at 11:20
  • $\begingroup$ it's for controlling the amount of gas produced, the supply is not completely controlled and the application call for different flow rates $\endgroup$ Mar 28, 2022 at 11:27
  • $\begingroup$ Sorry. I do not understand a word of your explanation. $\endgroup$
    – Maurice
    Mar 28, 2022 at 11:30
  • $\begingroup$ It's brown gas, just electrolyze water and mix the outputs. Huge safety concerns for the obvious reasons. Anyway it seems there is not much around so I guess it's time for practical tests! $\endgroup$ Mar 30, 2022 at 6:59
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    $\begingroup$ @Maurice Not "brown gas", but "Brown's gas" aka Oxyhydrogen $\endgroup$
    – Poutnik
    Mar 30, 2022 at 13:43

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