Understanding Electrochemistry: Anode and Cathode Reactions

[TJT]

Hi All,

I have a quick - probably quite basic - electrochemistry query I hope you can help with...

I have an anode and a cathode separated by water with current flowing between. There is some oxygen dissolved in the water so the reaction O2 + 2H20 + 4e -> 4OH occurs. Electrons flow out of the anode and into the cathode. At the anode, the electrons are used to convert O2 and H20 to OH (hydroxide). At the cathode electrons are removed to re-form O2 and H2) from the hydroxide?

My query is what proportion of the electrons are used in the anode/cathode reactions? If all the electrons are used for chemical reactions then is there no current flow?

Do you get zero current until you have converted all the O2 to OH? Doesn't seem likely to me but I'm sure I am missing something - I haven't done chemistry for a while...

Also, I know H2O is basically an insulator unless is has ionic substance in it so assume that there is some NaCl in the water and that this doesn't get involved in the reaction...

Would be grateful for any advice :-)

 

[Borek]

Dissolved oxygen is (almost) irrelevant. Typical products of the water electrolysis are oxygen and hydrogen (and they are products of electrode reactions, just google it).

 

[TJT]

Thanks for the really helpful advice...

I am looking at an experiment which definitely has the O2 + 2H20 + 4e -> 4OH reaction occurring but anyhow, my question is also applicable to the 2H20 -> O2 + 4H + 4e reaction. Do all the electrons flowing across the electrode boundary participate in the reduction/oxidation reactions?

If all then is there no current flowing through the electrolyte occupying the space between the electrodes?

If not all then how can I calculate the proportion?

 

[Borek]

Do all the electrons flowing across the electrode boundary participate in the reduction/oxidation reactions?

Yes, that's how they move across the phase boundary.

If all then is there no current flowing through the electrolyte occupying the space between the electrodes?

Sure there is - electrons go into solution on one electrode and get out of the solution on the other electrode. To do so they have to travel through the solution - that's the current flowing.

 

[TJT]

Thanks for the help - it is appreciated