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I'm interested in electrolysis of water to form O$_2$ and H$_2$, as pure as possible given the constraints of a "household chemical" setup. I've read other questions on here (in particular, Best Settings for Electrolysis of water, Does the electrolysis of water produce chlorine gas?, Why would water, and not saltwater, undergo electrolysis? and others), but still have some open questions, in particular concerning the used electrolyte and the material of which the anode/cathode are.

Electrolyte

I'll be using tap water for my reaction that is not chlorinated. However, unspecified salts/impurities might be present that I cannot closer define, but we're talking about infant-safe drinking water (with little Na present). To have an efficient reaction, I will need to dissolve an electrolyte. There are many choices:

  • NaOH (lye): As far as I can tell, the "ideal" candidate for my requirements, but might not be present in a household and might be difficult to obtain. Should form pure H$_2$ and O$_2$ if I am not mistaken.
  • NaCl (table salt): Present in every household. Greatest drawback is that as far as I read Chlorine gas is formed during the electrolysis. My question would be, is the Chlorine emitted at the H$_2$ or O$_2$ electrode?
  • NaHCO$_3$ or KHCO$_3$ (baking powder): Present in every household. Does not form Chlorine gas. However, as far as I have read, forms CO$_2$, but again I'm unsure at which electrode.

Electrode material

We can forget platinum and gold right off the bat for price reasons. Stainless steel would be a good choice, but I've also read that pure Nickel sheets should be working well. My main concern is corrosion and passivation of the electrode material which then slows down the overall reaction. Would Nickel sheets be preferrable over stainless steel? If we use some material that does corrode easily (e.g., regular steel or just run-of-the-mill hardware store items that are some combination of galvanized iron), would the corrosion and solutoin of the metal in the water affect the gas quality? If so, how?

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  • $\begingroup$ What is the purpose of this home water electrolysis ? $\endgroup$
    – Poutnik
    Mar 14 '20 at 5:31
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    $\begingroup$ Stainless is good, no corrosion, conductive, won't affect gas quality. Graphite is good too. $\endgroup$
    – PReiser
    Mar 14 '20 at 6:28
  • $\begingroup$ The best choice is sulfuric acid, or sodium sulfate. With NaCl, you obtain mainly chlorine gas at the anode. This gas will get partly dissolved in the water, then will react with NaOH produced at the cathode, producing sodium hypochlorite. With sodium sulfate and sulfuric acid, you obtain H2 at the cathode and O2 at the anode. $\endgroup$
    – Maurice
    Mar 14 '20 at 11:02
  • $\begingroup$ Use magnesium sulfate heptahydrate, also known as Epsom salt. It is inexpensive, available in grocery and drug stores (people soak their feet in solutions of it), safe, and works well. Also, sodium bicarbonate is baking soda, not baking powder (a mixture that contains some baking soda). Potassium bicarbonate is just that. For electrodes, use stainless steel, nickel or graphite. You can buy graphite rods very inexpensively on eBay. $\endgroup$
    – Ed V
    Apr 23 '20 at 2:01

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