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I am basically trying to understand a concept in electrochemistry. I have a power source and am connecting the negative end of the power source to a working electrode (metal electrode). Will electrons flow out or into the metal electrode?

Details: I connect both poles to set up a complete circuit. I connect the negative pole to a platinum electrode and the positive pole to a Ag/AgBr electrode. I am interested in steady state effects in this scenario.

flaudemus
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Vijay Dandapani
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  • Please make your question more precise: do you connect only one pole of the power source and leave the other unconnected, or do you connect both poles to set up a complete electrical circuit? If the former is the case, are you interested in transient effect occuring when you connect, or in steady state effects? – flaudemus Feb 17 '19 at 10:48
  • @flaudemus Sorry for not being precise. I connect both poles to set up a complete circuit. I connect the negative pole to a platinum electrode and the positive pole to a Ag/AgBr electrode. I am interested in steady state effects in this scenario – Vijay Dandapani Feb 17 '19 at 18:01

2 Answers2

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Since you tagged your question with [electrochemistry] I assume you connect both plugs of your power source to 2 electrodes.

Because you connect the negative power plug to your metal electrode, this electrode gets negatively charged too.

Now you know that in the metal (of cable and electrode) only the negative electrons can move, and the positive atomic cores stay at rest.

That means, electrons flow into that electrode.

Thomas Fritsch
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    How would you know? The electrode was not grounded, it was in the solvent, its potential depends on chemistry, and on the potential that the solvent was at. –  Feb 17 '19 at 10:24
  • @Pieter Well, (of course?) I assumed he connected the positive power plug to the other electrode. – Thomas Fritsch Feb 17 '19 at 10:30
  • Potentials are relative, charge state is not. It can easily happen that both the positive and the negative terminal of a power source have the same sign of charge. And objects at ground potential can have a lot of charge (think capacitors). If you make assumptions, it is best to state them explicitly. –  Feb 17 '19 at 11:12
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    @Pieter you are right, I've edited my assumption into the answer – Thomas Fritsch Feb 17 '19 at 12:01
  • @ThomasFritsch Thank you for your answer and comments and a healthy discussion. I connect both the positive and the negative ends of the power source to two electrodes. Sorry, but how do I physically understand this. Does not the electron flow depend on the work function or Fermi level of the metal electrode I am connecting to ? Why is not the electron flow from my metal electrode to the power source ? Excuse me if the question is too elementary. Thanks ! – Vijay Dandapani Feb 17 '19 at 18:11
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    So the solvent cannot sustain a buildup of charge to an appreciable level. Less than a ms of current may flow towards an electrochemical reaction. Both an anodic and cathodic reaction need to occur to maintain electroneutrality in the bulk of the fluid – ChemEng Mar 30 '22 at 12:09
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So if you know what a capacitor is you know that it will charge the metal plate and the voltage between the 2 plates (or one plate and remaining terminal in this case) will be the voltage of the battery. So if 2 batteries are disconnected this will not be the case or if the anode and cathode are separated say just 2 pieces of metal in air then again no appreciable voltage drop (not like a battery setup). In a battery the reaction does proceed even disconnected(in the external circuit) up to the specified voltage at which the reaction stops due to charge buildup.

In your case it is good to know metals like to be oxidised thus connecting a piece of metal to a negative terminal actually provides electrons and reduces it preventing rust (this is known as cathodic protection)

Typically the Fermi energy level is related to the concept of thermocouples in millivolts not battery chemical reactions in volts

Joe Banden
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