In electrochemistry, ITIES (interface between two immiscible electrolyte solutions) is an electrochemical interface that is either polarisable or polarised. An ITIES is polarisable if one can change the Galvani potential difference, or in other words the difference of inner potentials between the two adjacent phases, without noticeably changing the chemical composition of the respective phases (i.e. without noticeable electrochemical reactions taking place at the interface). An ITIES system is polarised if the distribution of the different charges and redox species between the two phases determines the Galvani potential difference. Usually, one electrolyte is an aqueous electrolyte composed of hydrophilic ions such as NaCl dissolved in water and the other electrolyte is a lipophilic salt such as tetrabutylammonium tetraphenylborate dissolved in an organic solvent immiscible with water such as nitrobenzene, or 1,2-dichloroethane.
Charge transfer reactions of an ITIES 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
Δ o w ϕ = ϕ w − ϕ o = Δ o w ϕ i ⊖ + R T z i F ln ( a i o a i w ) {\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 Δ o w ϕ i ⊖ {\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.
Δ o w ϕ i ⊖ = Δ G t r , i ⊖ , w → o z i F {\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
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