A three-compartment electrolytic cell for anodic oxidation of sulfur dioxide and cathodic production of hydrogen☆

Abstract A three-compartment electrolytic cell with a minimized ohmic resistance avoiding the cathodic reduction of sulfur dioxide was constructed. Since sulfur dioxide penetrates all separators studied, sulfur dioxide migration from anode to cathode compartment is prevented by an additional electrolyte flow through an intermediate compartment. The intermediate compartment is limited by two cation exchanger membranes in order to avoid electrolyte interchange by pressure variations. NEOSEPTA membranes turned out to be stable at sulfuric acid concentrations up to 55 w/o and 90°C. Resistivity is sufficiently low. Graphite felt flow-through electrodes fitted onto the membranes and additional catalysts were used. Other cell materials were impregnated graphite, PVDF and copper. The cell voltage was 455, 565, 665, 770, 880 mV at 100, 200, 300, 400, 500 mA cm −2 , respectively, with 50 w/o sulfuric acid at 88°C.