Three major classes of charge transfer reactions can be studied at an ITIES:

• Ion transfer reactions
• Assisted ion transfer reactions
• Heterogeneous electron transfer reactions

The Nernst equation for an ion transfer reaction reads

${\displaystyle \Delta _{\text{o}}^{\text{w}}\phi =\phi ^{\text{w}}-\phi ^{\text{o}}=\Delta _{\text{o}}^{\text{w}}\phi _{i}^{\ominus }+{\frac {RT}{z_{i}F}}\ln \left({\frac {a_{i}^{\text{o}}}{a_{i}^{\text{w}}}}\right)}$ ,

where ${\displaystyle \Delta _{\text{o}}^{\text{w}}\phi _{i}^{\ominus }}$  is the standard transfer potential defined as the Gibbs energy of transfer expressed in a voltage scale.

${\displaystyle \Delta _{\text{o}}^{\text{w}}\phi _{i}^{\ominus }={\frac {\Delta G_{tr,i}^{\ominus ,{\text{w}}\rightarrow {\text{o}}}}{z_{i}F}}}$ 

The Nernst equation for a single heterogeneous electron transfer reaction reads

${\displaystyle \Delta _{\text{o}}^{\text{w}}\phi =\Delta _{\text{o}}^{\text{w}}\phi _{\text{ET}}^{\ominus }+{\frac {RT}{F}}ln\left({\frac {a_{{\text{R}}_{1}}^{\text{w}}a_{{\text{O}}_{2}}^{\text{o}}}{a_{{\text{O}}_{1}}^{\text{w}}a_{{\text{R}}_{2}}^{\text{o}}}}\right)}$ ,

where ${\displaystyle \Delta _{o}^{\text{w}}\phi _{\text{ET}}^{\ominus }}$  is the standard redox potential for the interfacial transfer of electrons defined as the difference the standard redox potentials of the two redox couples but referred to the aqueous standard hydrogen electrode (SHE).

${\displaystyle \Delta _{\text{o}}^{\text{w}}\phi _{\text{ET}}^{\ominus }=\left[E_{{\text{O}}_{2}/{\text{R}}_{2}}^{\ominus }\right]_{\text{SHE}}^{\text{o}}-\left[E_{{\text{O}}_{1}/{\text{R}}_{1}}^{\ominus }\right]_{\text{SHE}}^{\text{w}}}$ 

To study charge transfer reactions of an ITIES, a four-electrode cell is used.

Two reference electrodes are used to control the polarisation of the interface, and two counter electrodes made of noble metals are used to pass the current. The aqueous supporting electrolyte must be hydrophilic, such as LiCl, and the organic electrolyte must be lipophilic, such as tetraheptylammonium tetra-pentafluorophenyl borate.

Contrary to a neutral solute, the partition coefficient of an ion depends on the Galvani potential difference between the two phases:

${\displaystyle P_{i}={\frac {a_{i}^{\text{o}}}{a_{i}^{\text{w}}}}=\exp \left[{\frac {z_{i}F}{RT}}(\Delta _{\text{o}}^{\text{w}}\phi -\Delta _{\text{o}}^{\text{w}}\phi _{i}^{\ominus })\right]=P_{i}^{\ominus }\exp \left[{\frac {z_{i}F}{RT}}\Delta _{\text{o}}^{\text{w}}\phi \right]}$ 

When a salt is distributed between two phases, the Galvani potential difference is called the distribution potential and is obtained from the respective Nernst equations for the cation C⁺ and the anion A^– to read

${\displaystyle \Delta _{\text{o}}^{\text{w}}\phi ={\frac {\Delta _{\text{o}}^{\text{w}}\phi _{\text{C+}}^{\ominus }+\Delta _{\text{o}}^{\text{w}}\phi _{\text{A-}}^{\ominus }}{2}}+{\frac {RT}{2F}}\ln {\left({\frac {\gamma _{\text{C+}}^{\text{o}}\gamma _{\text{A-}}^{\text{w}}}{\gamma _{\text{C+}}^{\text{w}}\gamma _{\text{A-}}^{\text{o}}}}\right)}}$ 

where γ represents the activity coefficient.

• Ionic partition diagram
• Distribution law
• Ion transport number