Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag2+ from Ag+ in 6 M HNO3 anolyte has been studied with 6 M HNO3 or 3 M H2SO4 as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO3 is generally used as catholyte, which, however, produces NOx gases in the cathode compartment. The performance of the cell with 6 M HNO3 or 3 M H2SO4 as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag+ to Ag2+ conversion efficiency in the anolyte, (iii) the migration of Ag+ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H2SO4 catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H2SO4 concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H2SO4 as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.