[Lex Moen]

I want to build a construction for the electrolysis of water (such as the Hofmann apparatus) but one that can work with salt water, sea water f.i. .what electrodes would be best to use in such an aggressive medium?

[Arkcon]

Platinum.  Hey, you said best.  You said nothing about cost effective.  Graphite electrode aren't bad.  But just about any electrode is prone to wear and tear, over the (very) long run.

[Lex Moen]

suppose I use platinum electrodes in seawater (hofmanns apparatus) . to electrolyse water.
do you think there is a risk of producing chlorine gas or other sideproducts?

[Arkcon]

Yes, if the electrolyte or other dissolved solids are chlorides then you will produce chlorine, and not oxygen.  The choice of electrode has no effect on this.

(and please don't create a new thread to followup the same question, it makes it hard for us all to see what's been said and to combine all our thoughts)

[Lex Moen]

ok - sorry

so I produce chlorine. but at the other electrode, i do produce hydrogengas?

[vmelkon]

Yes, you get hydrogen at the negative electrode. You can use almost any conductor for the cathode and it won't degrade.

[billnotgatez]

There has been a discussion of this in the past and there is a belief that you are not limited to Chlorine at the positive electrode.

http://www.chemicalforums.com/index.php?topic=44669.0

I always thought you got Chlorine until the Sodium Chloride was depleted and then you would get Oxygen until the water is depleted.
But, if you peruse this forum you do not always get that as the answer.

In all cases of discussion I only say Hydrogen for the negative electrode.

[Lex Moen]

thanx, you were very helpfull and gave me usefull comments :-)