The redox reaction of 1,F-diheptyl-4,4'-dipyridinium dibromide in water was investigated by means of linear potential sweep voltammetry. It was found that aging of the radical salt film or the occurrence of the second reduction step results in an additional oxidation peak. This additional oxidation peak is accompanied by a decrease of charge efficiency, leading to display failure, it was demonstrated that these problems can be largely avoided by use of modified viologens in combination with tin dioxide electrodes. The influence of the electrode material was also investigated.

The reduction peak of a linear potential sweep voltammogram of 1,1'-diheptyl-4,4'-dipyridinium dibromide in water, was found to be very steep with E, --Ep/2 ~-0.020V at a scan speed less thsn 0.1 V/,cec. This behavior was discussed on the basis of a model consisting of a reversible electron transfer and a coupled chemical reaction in analogy with reversible metal deposition. With modified viologens similar results have been obtained. The role of the coupled chemical reaction was underlined by the observed Nernstian dependence on cation and/or anion concentrations of both first and second reduction peak potential. The observed anodic peak of the first reduction step differs from the peak expected from the dissolution of a bulk deposit.