In cathode electrode compound like Li[Ni0.5Mn1.5]O2, how the electrochemical potential of cathode differ with Redox potential of Ni and Mn? Is it directly proportional? Is there any theory behind it ? Thank you for your time !!
Hi Bebik
When one talks about an electrochemical potential of a cathode electrode of a pure element, i.e., Ni & Mn, one would talk about the reduction reaction of an electrochemical half-cell, M+n+ne----M. The corresponding potential of such electrochemical half-cell is called the Redox potential of the pure element. It is well known that the Redox potential of the electrochemical half-cell can be described by the Nernst equation;
E=E0-[RT/ZF] ln[ aRed/aOx]
where
E is the Redox potential of the electrochemical half-cell of the pure element.
E0 is the standard potential of the reversible reaction of the pure element, in which reduction & oxidation reactions occur in a reversible manner.
R is the universal gas constant: R =8.314472(15) J K−1 mol−1
T is the temperature in kelvins.
F is the Faraday constant, the number of coulombs per mole of electrons:
F =9.64853399(24)×104 C mol−1
Z is the number of moles of electrons transferred in the cell reaction or half-reaction.
a is the chemical activity for the relevant species, where aRed is the activity of the reduced form and aOx is the activity of the oxidized form.
In contrast, when one talks about a cathode electrode in a compound form like;
Li[Ni0.5Mn1.5]O2 , in this case the electrochemical potential can be described by the Nernst equation with the summation of all terms of the elements involved in the compound;
Summation of E= Summation {E0-[RT/ZF] ln[ aRed/aOx]}
of all terms of the elements involved in the compound.
I appreciate your time Dr. Habib. Thank you very much for such a wonderful explanation. Regarding the Nernst Equation, correct me if i am wrong about this conclusion that if i want higher potential from my electrode, i should use material with higher Redox potential?
Dear Bibek
I meant to include E0 for Ni, Mn, Li, andO2 in the Nernst Equation.
Also, to include aRed and aOx for Ni,Mn,Li, andO2 in the Nernst Equation.
so, Nernst equation will be used with the summation of all terms of the elements involved in the compound.
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