Gold anode seems to dissolve in sodium hydroxide electrolyte

[tobuslieven]

Doing some tests using a gold electrode to split water. Basically I'd like to know if you'd expect what I'm seeing, which is a brown gunk building up on the gold anode and it seeming to be eroded. I was expecting it not to react at all.

Set up:

• 1 micron thick 24 carat gold foil at the positive electrode. 2 square cm. Legit supplier of gold foil.
• Titanium negative electrode. 4 square centimetres.
• Sodium hydroxide solution electrolyte.
• 20 volts.

I see 2 amps or so flowing and plenty of bubbles, and unfortunately the gold electrode discolours, some brown gunk builds up on it, and the edges look like they're getting eaten away.

I saw in the topic below that someone mentioned the possibility of gold hydroxide being formed. I'm thinking it's either this, or my gold foil isn't as pure as claimed.

Does anyone have any opinion or experience of this situation, and how likely the gold hydroxide is? If it's this, might a potassium hydroxide electrolyte be worth a shot, or if the gold hydroxide is forming, should I give up on the gold anode?

Apologies, I have very limited chemistry knowledge, but willing to learn. Cheers.

 

[Sensei]

Gold from unknown source, can have 24 carats (24/24=100%), can have 18 carats (18/24 = 75%) or it can have 14 carats (14/24 = 58%).. (rarely different than 24/18/14)

Somebody lied to you, and sold you, not 24 carats Gold, I am afraid so..

Measure mass of "gold electrode" using electronic weight with high precision i.e. 0.1g or better precision.. Then use it as electrode.. for hours.. and then measure mass again.. Calculate, and you will learn how many carats it used to have..

 

[tobuslieven]

1 hour ago, Sensei said:

Somebody lied to you, and sold you, not 24 carats Gold, I am afraid so.. Measure mass of "gold electrode" ... Then use it as electrode.. for hours.. and then measure mass again

Thanks for the reply, and that's a cool idea, but mass measurements aren't going to be possible as the total weight of the electrode is about 0.004g (gold 20grams per cubic centimetre, 1micron is 1/10,000 cm, electrode 1cm by 2 cm by 1 micron). I don't have that precision available.

Can I take it from your reply that you are certain 24 carat gold will not behave as I described? Thanks again for the input.

[tobuslieven]

I've found out that I might be able to use someone's X-ray florescence machine to test the gold foil. Hopefully I'll report back tomorrow.

[Sensei]

5 hours ago, tobuslieven said:

Can I take it from your reply that you are certain 24 carat gold will not behave as I described? Thanks again for the input.

I have 24 carat Gold, and it's not dissolving when it's used as electrode during typical electrolysis of water...

 

Edited July 23, 2018 by Sensei

[tobuslieven]

I took the gold to a gold shop and they said it was 24 carat gold. They used their X-ray florescence machine on it and they'd have no reason to exaggerate the gold content as they use the assay to value gold that they buy from customers.

I'm going to have another go with another piece from the same source but this time I'll use deionised water with sodium hydroxide instead of tap water. Maybe there was some chlorine in the tap water attacking the gold, or the fluoride in the water messing with it. Does that sound likely to anyone?

Will report back later.

[tobuslieven]

I just realised, putting 2 amps at 20 volts through 2 square cm of gold foil might be too much for it to handle. On King of Random's water splitter, video below, his anode area is something like 1500 square cm and he's putting 12 volts and 20 amps through them. My anode area is about 1/1000th of his, so should I make sure I'm only putting 1/1000th of his wattage through it? That would mean something like 0.25 a watt for my system. Maybe 4 volts 1/16 amp.

Still working on my next test. Here's King of Random's video. Maybe I was just heating up the gold foil so much that all sorts of weird reactions were becoming possible in the caustic soda, despite gold not being very reactive generally.

 

[John Cuthber]

It's possible that mechanical damage caused by the bubbles is at least part of the issue.

 

All the gold leaf I have seen was (practically) 24 carat.

Adding any impurity makes it much harder to form into such thin sheets.