I'm separating water into hydrogen and oxygen by connecting a DC current to 99.9% pure nickel electrodes in a solution of NaOH in deionized water.

It works great, except that any attempts to increase the rate of production by increasing current, increasing NaOH, bringing electrodes closer together, etc. also result in an increase in heat.

At the moment the bottleneck for my production rate is trying to keep the water from boiling or otherwise causing heat damage to the apparatus.

I've considered investing in a cooling system, but I'm also interested in knowing whether or not it is possible to somehow improve the efficiency of the electrolysis and thereby improve separation rate without increasing heat.

(In case you're wondering, I'm using hydrogen to fill balloons. It works quite well, I can fill a normal sized balloon in a few minutes, but then I need to wait an hour for everything to cool down. (Yes I know hydrogen and fire don't mix well.))


1 Answer 1


Consider the electrolysis apparatus as a resistor in series with an EMF. Ideally, the cell voltage should be just enough to overcome the EMF (potential needed to split water), but some over-voltage is inevitable to have a decent current flow. Much of the heating is due to this wasted over-voltage. Then, to increase the efficiency and reduce heating, it's necessary to reduce the series resistance.

$\ce{NaOH}$ is already highly ionized, so adding more, beyond a certain point, is not the solution (no pun intended;). Close spacing helps, but you must leave room to physically separate $\ce{H2}$ from $\ce{O2}$. The remaining variable is electrode area: make the electrodes as large as feasible. You can further increase area by using porous sintered, or at least coarsely-sanded electrodes.

Quantum Sphere Inc. claims to produce a more active electrode from $\ce{Ni-Fe}$ particles, though they're probably a bit pricey for filling hydrogen balloons. Perhaps they offer samples?

BTW, I assume you're using a moisture trap for the gas, otherwise bubbling hot caustic electrolyte would inadvertently wind up in the balloon, reducing lift, damaging the balloon and possibly causing severe chemical burns. $\ce{NaOH}$ is called "caustic soda" for good reason!

  • $\begingroup$ I know, everyone says that you only need 1.3 volts or whatever to electrolyse water, but I've tried 5V vs 12V and there is much, much, more volume of gas produced at 12V. I'm using large nickel sheets so surface area is good. People also say that you only need a spoonful of NaOH, but generally the more I add the more gas (and heat) I produce. $\endgroup$ Commented Jul 31, 2017 at 19:03
  • $\begingroup$ What is a moisture trap? I ran the output through 2 meters of tubing submerged in cold water to reduce water vapour in the product. Although it doesn't really catch much so I don't really bother anymore. $\endgroup$ Commented Jul 31, 2017 at 19:08
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    $\begingroup$ A moisture trap can be as simple as a tube filled with glass wool to catch the condensing water vapor and "spitting" from a reaction such as electrolysis, or the tubing you mentioned. For dryer H2, the tube can be filled with CaCl2 or other desiccant, which is not needed for balloons. See thevespiary.org/rhodium/Rhodium/chemistry/filt/filtration_files/… for an idea of how to make one from a flask. Keep the trap small, and preferably of plastic rather than glass, to reduce mixing the H2 with residual air and to reduce shrapnel in the event of hydrogen igniting. $\endgroup$ Commented Aug 1, 2017 at 17:12
  • $\begingroup$ Oh, right, I gotcha, I remember that water absorbing setup from chemistry class. I have a load of silica gel packets, will those work instead of CaCl2? $\endgroup$ Commented Aug 1, 2017 at 20:28
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    $\begingroup$ Yes, even better than CaCl2, in that it won't dissolve in condensed moisture, and is easily dried for reuse in an oven. $\endgroup$ Commented Aug 2, 2017 at 1:38

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