What metals are safe to use as electrodes when doing electrolysis of water (I am trying to produce hydrogen gas)

Question

I am going to be a DC power converter (with fairly high voltage and amps) to turn water into hydrogen (and oxygen) gases. However I have a few questions about the safety of this process.

1. What electrolyte should I use in the water? I was thinking of using Magnesium sulfate (epsom salt) or Sodium bicarbonate (baking soda).

2. What metal should I use for the electrodes? I am not sure if graphite is conductive enough to be efficient. I want to use stainless steel, but have heard this may produce hexavalent chromium. Is this true? What about iron or copper? Are these safe? Do they produce any other toxic byproducts? (I would use platinum or platinum-coated titanium, but these are expensive).

Is it safe to use these electrolytes and electrolytes together? Thanks!

Answer 1

Magnesium sulfate is not the best choice when carrying out an electrolysis. Because, near the cathode, the solution becomes basic, and magnesium hydroxide $\ce{Mg(OH)2}$ will be produced, and it is poorly soluble. So the solution will soon become more and more turbid.

Sodium bicarbonate is not a better choice, because first it is not very soluble. Solutions have to be as concentrated as possible, to get a good yield. Second in the anode region, some $\ce{CO2}$ will soon be mixed with oxygen, due to the solution becoming acidic.

Graphite is a good conductor, and is efficient in electrolysis. But it has a tendency to crumbling. Tiny grains of black stuff are continuously produced at the surface of the anode, and fall back on the bottom of the container. This is disagreeable. Iron, copper and stainless steel are all slowly corroded by oxidation at the anode.

The best practical method for producing hydrogen by electrolysis is using platinum electrodes in a $\ce{H2SO4}$ or $\ce{Na2SO4}$ solution

Answer 2

Also, Faraday's experiments with electrolysis for the production of hydrogen from water resulted in the discovery that it takes between 0.5v and 1.24 volts to split a water molecule, anything more exponentially increases molecular movement, i.e. raises temperature, like an electric coffee pot. Amperage requirements depend on surface area of the electrodes. Lye in water solution and stainless steel electrodes, graded for corrosion prevention like 316 or 405 stainless, are sufficient and economical, butter knives work wonderfully for a quick demo, platinum definitely best, bare loose computer hard drive disks are plated lightly and work well, but if you aren't doing the electrolysis for profit, then stainless will work. In this cell, as the water is electrolyzed into lighter than air H and O2, the naturally rise out but the lye stays in solution and a single cell voltage of 1.5v contributes very little if any heat, so the experiment can be maintained by simply adding water to maintain coverage of the electrodes... Under a venthood if indoors, hydrogen will gather at the ceiling and any small spark will ignite it explosively especially with the increased oxygen, or in a closed cell the "dihydroxy" gas can be piped into a combustion engine or separated by electromagnet in a clear pipe divided, and fed into an acetylene oxy torch setup with the H in substituted for acetylene.