Membrane electrolysis for Bunsen reaction of the SI cycle

Bunsen reaction was carried out in a two-compartment membrane electrolysis cell having Nafion 117 as a separator between the compartments. Platinum and graphite, used as electrodes in the cell, were characterized by using linear sweep voltammetry (LSV) and cyclic voltammetry (CV). Electrolysis was carried out at 300 K, in constant current mode with current density in the range of 1.5–4.7 A/dm2. Aqueous solutions of ∼5.0 N HI containing dissolved iodine, with I2/HI ratio in the ratio of 0.25–1.5 were used as catholyte solution. Aqueous solution of 10 N sulphuric acid saturated with dissolved SO2 was used as anolyte solution. The concentration of dissolved SO2 in the anolyte was maintained by continuously bubbling SO2 in anolyte at atmospheric pressure in first set of experiments, and by maintaining a SO2-atmosphere at 1 bar (g) in another set of experiments. Volume of the anolyte changed in the first set of experiments and so current efficiency determination became difficult. In the other set of experiments, the increase in concentration of acids in the two compartments compared well with the amount of charge supplied during electrolysis with current efficiency of the cathode in the range of 90–95% and that of anode in the range of 100–110%. Current–voltage characteristic of the electrolysis cell was determined and the cell voltage was found to vary linearly with an increase in current density. The cell voltage increases with increase in initial concentration of sulphuric acid in anolyte from 10 N to 14.3 N and decreased with increase in value of I2/HI ratio in the catholyte.

► Membrane electrolysis can be used for Bunsen reaction at iodine concentration much lower than the traditional direct contact method.
► Current efficiency close to 100% indicating absence of side reactions.
► Cell voltage increases with increase in I2/Hi ratio.
► Cell voltage increases with increase in concentration of sulphuric acid beyond 10 N.