Studies on the depolarization characteristics of nitrobenzene at a rotating amalgamated cathode

Abstract

The depolarization characteristics of nitrobenzene were studied using an amalgamated rotating micro-disk cathode of copper in sulphuric acid medium. The cathode potential change with cd was followed with and without the addition of nitrobenzene under different conditions. With 30% sulphuric acid, the plot of potential/log cd is linear and when nitrobenzene is added and held in suspension, the cathode potential is considerably shifted to less negative values, indicating good depolarization at all cd's. However, when nitrobenzene is brought into homogenous solution by the addition of ethyl alcohol, good depolarization was observed only at low cd (< 10 A/dm 2); at high cd, the potential rapidly shifted to the hydrogen-evolution potential. When acid saturated with sodium sulphate is used, the potential/log cd plot has two distinct parts with different slopes. At cd > 2 A/dm 2), Na + discharge occurs and the reaction appears to be hydrogen evolution on a sodium-amalgam surface. With 10% and 5% sodium sulphate in the acid bath, inflexions occur in the potential/log cd curves at higher current densities. Addition of nitrobenzene to these baths containing sodium sulphate gives good depolarization only at the lower cd range. Addition of ethyl alcohol is again found to lower the depolarization effect of nitrobenzene. The effects are interpreted in terms of the zero-charge potential of the cathode.