Dear all!
How ionic migration works to be able to close an electric circuit when electrodes (let's say platinum or graphite) are immersed in a salt aqueous solution and there is no water electrolysis?
When a voltage is applied across the electrodes, electrons move through the external circuit and ionic double layers with opposite charges are created. To maintain electrical neutrality in the solution, ions in the double layer dynamically redistribute, adjusting their positions to counterbalance the electron flow in the external circuit. For example: At the cathode, Na+ ions are drawn closer to the electrode surface, balancing the incoming electrons. At the anode, Cl− ions migrate toward the electrode, balancing the deficit of electrons. These processes are supposed to effectively allow the transfer of charge between the external circuit and the ionic solution without requiring a direct chemical transformation (like water electrolysis). To be more specific, this is the part that I can not easily explain by myself. At least, I can elucidate somehow that the moving ions with their electric field, as they approach from the diffusive to the inner or Helmholtz layer, become able to push and stimulate the charge carriers already existing in the side of the solid electrode.
This is important to understand the role of supporting electrolytes
Best
Marco
Ions will move to cathode and anode according to charge. To maintain a current, some electron transfer has to happen at the electrodes. this can be reduction and oxidation of the ions, can be intercalation, can be water electrolysis.
Filip Ponsaerts , thanks but
When a voltage is applied across the electrodes, electrons move through the external circuit and ionic double layers with opposite charges are created. To maintain electrical neutrality in the solution, ions in the double layer dynamically redistribute, adjusting their positions to counterbalance the electron flow in the external circuit. For example: At the cathode, Na+ ions are drawn closer to the electrode surface, balancing the incoming electrons. At the anode, Cl− ions migrate toward the electrode, balancing the deficit of electrons. These processes are supposed to effectively allow the transfer of charge between the external circuit and the ionic solution without requiring a direct chemical transformation (like water electrolysis). To be more specific, this is the part that I can not easily explain by myself. At least, I can elucidate somehow that the moving ions with their electric field, as they approach from the diffusive to the inner or Helmholtz layer, become able to push and stimulate the charge carriers already existing in the side of the solid electrode.
Charge transfer at the electrode-electrolyte interface involves the electric double layer at the interface between a charged surface of the electrode and an electrolyte solution.
This double layer is divided into the inner Helmholtz Plane and the outer Helmholtz Plane.
The inner is the layer of ions adsorbed onto the electrode surface.
The outer consists of solvated ions that are attracted to the electrode surface but are not adsorbed yet.
The charge transfer process at the electrode-electrolyte interface involves several steps:
1) Ions in solution migrate towards the electrode surface due to the potential gradient.
2) Ions from the solution are adsorbed and lose their solvation shell.
3) Electrons are transferred between electrode and ion.(redox reaction)
4) After redox, the ion, has a different charge and desorbs.
Without redox, intercalation or the like, the behaviour will be like a capacitor.
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