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Topic: Electrolysis question  (Read 1643 times)

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Offline wachanna

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Electrolysis question
« on: July 01, 2021, 04:48:01 PM »
Hello all. Its my first day here. Im just a regular uneducated guy, with a curious mind. Let's get into it. If pure silver metal was used as both electrodes in a solution of sodium hydroxide, and 5 volts was applied to the circuit, would silver react with anything happening during electrolysis, or, would the silver electrodes essentially be a catalyst, meaning, be completely unreactive? Thanks for your thoughts.

Offline Borek

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Re: Electrolysis question
« Reply #1 on: July 02, 2021, 03:20:23 AM »
This isn't easy to answer.

In a well selected conditions silver can easily dissolve on anode and deposit on the cathode. I doubt that's the case in high pH of sodium hydroxide solution though. Silver is quite noble so chances are electrodes will be just inert and the only observed thing would be water electrolysis. Hard to say without spending time to consult Pourbaix diagrams for silver and without comparing them with potentials required for oxygen/hydrogen evolution at high pH.

And I would not call an inert electrode the catalyst, that is a misnomer.
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Offline wachanna

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Re: Electrolysis question
« Reply #2 on: July 02, 2021, 10:08:38 AM »
This isn't easy to answer.

In a well selected conditions silver can easily dissolve on anode and deposit on the cathode. I doubt that's the case in high pH of sodium hydroxide solution though. Silver is quite noble so chances are electrodes will be just inert and the only observed thing would be water electrolysis. Hard to say without spending time to consult Pourbaix diagrams for silver and without comparing them with potentials required for oxygen/hydrogen evolution at high pH.

And I would not call an inert electrode the catalyst, that is a misnomer.

I just got done surfing the internet for Pourbaix diagrams. Its kinda sad this far into the evolution of the internet how difficult it is to get precise results when googling. I found some diagrams but not of silver and sodium hydroxide, but of silver and water that has oxygen and hydrogen dissolved into it. And all diagrams ive seen only go up to 2 volts. Which is helpful but a very very small window to see the world through. The silver diagram i spoke of said formation of various silver oxides around the voltage needed to produce hydrogen and oxygen via electrolysis in a high ph solution. I know there are formulas and test equipment for calculating exact ph, but like you said, sodium hydroxide solutions are high ph. Not sure if there is a diagram that says what happens with silver and sodium hydroxide, cause either the internet made good enough to yield that specific search result, or the diagram doesn't exist. I wouldn't know, but you might. All silver thoughts aside, is there a simple alternative cell configuration that uses super cheap components and has inert/unreactive electrodes to produce hydrogen and oxygen? I think part of the problem is finding a solution that is easier to work with, meaning, has more electrodes to choose from, that dont react with solution or gas products. Any ideas? Or, am i just blind to simple cheap unreactive electrodes that can be used in sodium hydroxide solution?

Offline Borek

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Re: Electrolysis question
« Reply #3 on: July 02, 2021, 01:37:01 PM »
I found some diagrams but not of silver and sodium hydroxide, but of silver and water that has oxygen and hydrogen dissolved into it.

Pourbaix diagram is about an element and pH, so you won't find it for Ag/NaOH - adding NaOH changes pH and that's all that matters.

Quote
And all diagrams ive seen only go up to 2 volts. Which is helpful but a very very small window to see the world through.

If you go to higher/lower voltages all that changes is the kinetics, stable compounds don't change (that is, unless you apply kV and the electrode evaporates ;) )

Quote
All silver thoughts aside, is there a simple alternative cell configuration that uses super cheap components and has inert/unreactive electrodes to produce hydrogen and oxygen? I think part of the problem is finding a solution that is easier to work with, meaning, has more electrodes to choose from, that dont react with solution or gas products. Any ideas? Or, am i just blind to simple cheap unreactive electrodes that can be used in sodium hydroxide solution?

Typical suggestions for water electrolysis are stainless steel (it gets oxidized, but is covered with very stable oxides so doesn't corrode further) and carbon/graphite. I don't remember how the stainless steel behave in high pH though, graphite should be better - but it is often kept in shape by some binder which doesn't have to be resistant to water/pH.
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Offline wachanna

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Re: Electrolysis question
« Reply #4 on: July 02, 2021, 04:32:06 PM »
I found some diagrams but not of silver and sodium hydroxide, but of silver and water that has oxygen and hydrogen dissolved into it.

Pourbaix diagram is about an element and pH, so you won't find it for Ag/NaOH - adding NaOH changes pH and that's all that matters.

Quote
And all diagrams ive seen only go up to 2 volts. Which is helpful but a very very small window to see the world through.

If you go to higher/lower voltages all that changes is the kinetics, stable compounds don't change (that is, unless you apply kV and the electrode evaporates ;) )

Quote
All silver thoughts aside, is there a simple alternative cell configuration that uses super cheap components and has inert/unreactive electrodes to produce hydrogen and oxygen? I think part of the problem is finding a solution that is easier to work with, meaning, has more electrodes to choose from, that dont react with solution or gas products. Any ideas? Or, am i just blind to simple cheap unreactive electrodes that can be used in sodium hydroxide solution?

Typical suggestions for water electrolysis are stainless steel (it gets oxidized, but is covered with very stable oxides so doesn't corrode further) and carbon/graphite. I don't remember how the stainless steel behave in high pH though, graphite should be better - but it is often kept in shape by some binder which doesn't have to be resistant to water/pH.

Thanks for the response, im going to keep thinking about all this. Have a good one

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