Recent developments in the technology of sulphur dioxide depolarized electrolysis

Abstract

The use of sulphur dioxide as an anode depolarizer in the electrolytic production of hydrogen can considerably reduce the electrical energy input to the electrolyzer. The present work deals with developments in the technology of SO₂-depolarized electrolysis. Recent achievements in electrode fabrication techniques and optimization of cell configuration have resulted in substantial improvements in both cell potential and performance stability. While operating in 50 wt% sulphuric acid at 50° C and 1 atm, the measured cell potentials at 200 and 400mA cm⁻² were ≈ 0.77 and 1.05V (including ohmic losses), respectively. A cell endurance test, performed at a constant current density of 100mA cm⁻², indicated that a stabilized cell potential of ≈ 675 mV was achieved after 80 hours of continuous operation. The resulting gas from the test cell contained 98.7 vol% hydrogen. The effect of acid concentration in the range 10–60 wt% on the performance characteristics of an SO₂-depolarized electrolyzer was also investigated. Experimental results revealed that the optimum acid concentration for operating SO₂-depolarized electrolyzers is approximately 30 wt%. The observed cell potential was only 0.71 V at 200mA cm⁻².