Adjusting the operating boundaries for the mitigation of SO2 crossover in sulphur depolarized electrolysers

Sulphur depolarized electrolysers (SDE) are a promising approach for hydrogen production, as they omit some of the problems present in water electrolysis (WE). In SDEs, SO2 is used as anodic feed, which lowers the theoretical potential to 0.158 V compared to the 1.23 V in WE. At the same time, this technology enables the utilisation of toxic waste gas such as SO2, while generating H2SO4 as a by-product. One of the key issues in SDE operation is the SO2 crossing over the membrane, which is then reduced in the cathode into elemental sulphur and can poison the catalyst and block the mass transport in the porous layers. Boundary studies on the operating conditions are performed to prevent cross over for a gas-fed SDE system by optimising the operating voltage, gas flow rates and catalyst loading. The effectiveness of the optimized conditions is evaluated over 4 h of continuous operation. It is shown that by maintaining a stoichiometry of 1.0 and a lower voltage boundary of 1.2 V, a current decrease of 0.1 mA/cm2h is obtained as compared to 20 mA/cm2h at a stoichiometry of 4.0 and a voltage of 1.0 V.