Indicator Electrodes and Their Potentials

3 Indicator Electrodes and Their Potentials II.9.3.1 Redox Electrodes 

When both the oxidised and the reduced forms of a redox couple are dissolved in a solution, an inert metal can attain a potential, which only depends on the ratio 

In the case of an electrochemical equilibrium, the Nemst equation follows  

2 to see the meaning of the formal potential (Ce ,Ce +). Such inert indicator electrodes are very suitable for the indication of redox titrations. 

Another example of a redox electrode with a homogeneous redox equilibrium is the so-called quinhydrone electrode for pH measurements reported by Biilmann in 1921 [1], Quinhydrone is a charge transfer complex consisting of quinone and hydroquinone in a 1 1 ratio. If this compound is placed into an aqueous solution, the chemical equilibrium appears as follows [2]  

---