Electrochemistry

When electrodes are placed in an electrolyte and a voltage is applied, the electrolyte will conduct electricity. Lone electrons normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the cathode consuming electrons from the cathode, and another reaction occurs at the anode producing electrons to be taken up by the anode. As a result, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge develops around the anode. The ions in the electrolyte move to neutralize these charges so that the reactions can continue and the electrons can keep flowing.

For example, in a solution of ordinary salt (sodium chloride, NaCl) in water, the cathode reaction will be

2H2O + 2e- > 2OH- + H2 and hydrogen gas will bubble up; the anode reaction is 2H2O > O2 + 4H+ + 4e-and oxygen gas will be liberated. The positively charged sodium ions Na+ will react towards the cathode neutralizing the negative charge of OH- there, and the negatively charged chlorine ions Cl- will react towards the anode neutralizing the positive charge of H+ there. Without the ions from the electrolyte, the charges around the electrode would slow down continued electron flow; diffusion of H+ and OH- through water to the other electrode takes longer than movement of the much more prevalent salt ions.

In other systems, the electrode reactions can involve the metals of the electrodes as well as the ions of the electrolyte.

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Electrolytic conductors are used in electronic devices where the chemical reaction at a metal/electrolyte interface yields useful effects.

* In batteries, two metals with different electron affinities are used as electrodes; electrons flow from one electrode to the other outside of the battery, while inside the battery the circuit is closed by the electrolyte's ions. Here the electrode reactions convert chemical energy to electrical energy.