Is a gold electrode supposed to corrode during electrolysis?

[Rhannmah]

Help! I was under the assumption that a gold electrode for oxygen would be able to sustain water electrolysis with sodium bicarbonate as the electrolyte without degrading, so I bought a foot long of 28 gauge 24k(pure gold) wire, but I've been putting it to the test for about 30 minutes and it's already starting to degrade!

Is this a behavior I should have expected? Have I been sold some non-pure gold? Admittedly, I've been putting some pretty heavy voltage through it to test the limits. Here's my experimental setup:

• 1 graphite anode for hydrogen evolution
• 1 pure gold wire for oxygen evolution
• 1 power supply feeding 15 volts and 0.7 amps through the circuit
• 1 saturated solution of sodium bicarbonate and water
• electrodes are spaced about 1 inch apart, the graphite electrode offering MUCH more surface area than the gold wire

Anyone can help me figure out what's going on? I'm at my wit's end, the gold wire has tarnished under minutes and has started to flake off. Under the microscope, it looks all rusted and i can't even tell it's gold anymore. Should I be doubting the purity of my wire? Should I lower my voltage? Is this normal?

 

[Jann Peter Simonsen]

Gold has a reputation for being a stable, non reaktive metal under most situations. However, I strongly suspect that your problem could lie in the use of carbon (graphite) as your cathode.
I haven't researched this, but try investigating the effects of passing current through carbon rods w.r.t. the production of small amounts of cyanide compounds (sodium cyanide) in your solution. If this occurs, gold will react with these ions, creating gold cyanide and the presence of sodium in your solution will possibly result in the following reaction:
4 Au + 8 NaCN + O2 + 2H2O → 4 Na[Au(CN)2] + 4 NaOH

 

[Rhannmah]

Well, I tried swapping hydrogen evolution electrodes; tried aluminium and copper, and I get roughly the same result. I've noticed that reheating the gold wire to melting point seems to revert the degradation.

I tried different, weaker voltages(like 5v) and I still get insanely quick degradation. I'm stumped.

 

[Jann Peter Simonsen]

I agree, it sounds very strange...I have no other suggestions, sorry! Hope you get it solved...

 

[NascentOxygen]

the gold wire has tarnished under minutes and has started to flake off.

It might be erosion or pitting by cavitation. You are liberating bubbles at the surface of the electrode, on a small scale these act like explosions. Gold is soft so might be easy to erode or roughen and this would give it a dull non-reflective appearance. The fact that you seem able to reverse the degradation by remelting the surface would seem to support this scenario.

I noticed this with my electrolysis experiments in junior high. I could start off with shiny smooth carbon rods with a high lustre, but after a while the submerged portion would have become roughened and dark, and particles of carbon that had flaked off could be seen in the electrolyte.

 

[Rhannmah]

So hardness may be a factor in the durability? Maybe iridium wire would be a solution. Don't know if it can survive such a high oxidation environment though. Maybe platinum/iridium wire.

 

[NascentOxygen]

Hardness, toughness, malleability, I'm not sure which. Are you doing this as a home experiment? I remember doing electrolysis using lead sheet for the oxygen-liberating electrode. As in lead acid battery chemistry, it becomes coated with CONDUCTIVE lead oxide^‡ (brown). You could try that? At the very least, its cheapness would enable you to use a much larger plate.

Perhaps we should ask @Borek to give an opinion of what you're seeing.

^‡ if the hydrogen liberating electrode is aluminium then you have an electrolytic rectifier

 

[Borek]

Perhaps we should ask @Borek to give an opinion of what you're seeing.

Sadly, not much to add. I never heard about such problems with gold electrodes.

 

[Rhannmah]

Yeah, I'm doing this at home so i don't want to use materials that might produce unwanted toxic byproducts or residue.

Could it simply be that the gold I have is not pure and is an amalgam?

 

[Baluncore]

Hardness, toughness, malleability, I'm not sure which.

Mechanical properties are not that important when it comes to electrochemistry. Stronger bonds may tend to have greater half-cell potentials before they are disrupted, but the difference in voltage is not much.

Admittedly, I've been putting some pretty heavy voltage through it to test the limits.

What I think you are saying is that you have been placing a higher voltages across the cell, in order to get more current flow through the cell, and so generate more gas.

Current decides the rate of reaction and so gas generation. Electrochemical reactions are voltage critical. You need sufficient voltage to overcome the cell EMF and the over-potential. Higher voltages will tear other chemical bonds apart and heat the solution by W=I²R. The energy efficiency of gas production falls as voltage increases. Remember that power is energy flow and is voltage multiplied by current. If you only have higher voltage available you are better to use the current several times by dividing the voltage over multiple electrolysis cells in series.

To increase the current, and so the rate of reaction, you could increase the conductivity of the electrolyte, increase the area of the electrodes or move them closer together. Once gas is being generated, attempting to increase the current by increasing the cell voltage may lead to consumption of, or plating onto, the electrodes in proportion to the current and rate of the reaction.

 

[Rhannmah]

One thing I've noticed is that when I tried using gold on both sides of the cell, only the oxygen producing side is getting damaged. The hydrogen side looks just fine. I'm having a hard time thinking of a reason other than my gold not being 99+% pure.

 

[Baluncore]

You can do anything with enough voltage. O^– is being transported one way while H⁺ and AU⁺ move in the opposite direction. O₂ and H₂ are released as gasses. If you are lucky, the Au etched from the oxygen gas electrode will be plated onto the hydrogen gas electrode and not lost with the electrolyte.

 

[Rhannmah]

Is there a way to prevent Au⁺ from being detached from the oxygen side while still producing oxygen?

 

[Baluncore]

Is there a way to prevent Au+ from being detached from the oxygen side while still producing oxygen?

Yes. Use a different electrode material and a lower voltage. Study this page.
https://en.wikipedia.org/wiki/Electrolysis_of_water

Electrode mechanical properties such as hardness are not important, the Electrochemical Series is very important.
https://en.wikipedia.org/wiki/Standard_electrode_potential
This table of relative half cell potentials that give the voltage (=energy) needed to move electrons between various ions.
https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)
That table contains the information needed to work out which reaction will progress and what voltage is needed to make it happen. You can write out the balanced equations needed to move all the electrons. Find the voltages in the table involving water and the electrodes in your process.

It is uneconomic to swap gold atoms for hydrogen gas. You should not use gold under conditions where it is being lost. Lower the voltage you are using until the reaction you need occurs without consumption of expensive electrodes. That voltage will be slightly more than 1.23 volts. Increase the electrode area and reduce the separation of plates to increase the gas yield. Maybe consider using a carbon electrode for the oxygen side.

 

[Rajiv Mohan]

Help! I was under the assumption that a gold electrode for oxygen would be able to sustain water electrolysis with sodium bicarbonate as the electrolyte without degrading, so I bought a foot long of 28 gauge 24k(pure gold) wire, but I've been putting it to the test for about 30 minutes and it's already starting to degrade!

Is this a behavior I should have expected? Have I been sold some non-pure gold? Admittedly, I've been putting some pretty heavy voltage through it to test the limits. Here's my experimental setup:

• 1 graphite anode for hydrogen evolution
• 1 pure gold wire for oxygen evolution
• 1 power supply feeding 15 volts and 0.7 amps through the circuit
• 1 saturated solution of sodium bicarbonate and water
• electrodes are spaced about 1 inch apart, the graphite electrode offering MUCH more surface area than the gold wire

Anyone can help me figure out what's going on? I'm at my wit's end, the gold wire has tarnished under minutes and has started to flake off. Under the microscope, it looks all rusted and i can't even tell it's gold anymore. Should I be doubting the purity of my wire? Should I lower my voltage? Is this normal?

Please take care of following:
1. Reduce the quantity of Sodium Bi
Carbonate. Saturated solution is toooo
much !

2. Since the surface area of Gold wire is too
little, reduce the current density. It should
have been a gentle process !

3. Voltage used is too much e.g. 15 Volts.

4. You are directly forcing the Gold electrode
to involve into reaction !

5. You have not mentioned the actual voltage
maintained across the electrodes. Is it
also 15 Volts DC or some Voltage drop
has occurred due to internal resistance of
your battery / power supply ?? Also, for
how many minutes the process was
Continued ?

6. Definitely, you are overdriving your system

Rajiv Mohan