Polybenzimidazole Membranes for Hydrogen and Sulfuric Acid Production in the Hybrid Sulfur Electrolyzer

The hybrid sulfur (HyS) thermochemical cycle has been investigated as a means to produce large quantities of clean hydrogen at efficiencies higher than those possible from water electrolysis. Recent studies have shown that traditional proton exchange membranes, such as Nafion, may limit HyS electrolyzer performance because concentrated sulfuric acid produced during electrolysis dehydrates the membrane. In this paper, we report the use of sulfonated polybenzimidazole (s-PBI) membranes in the HyS electrolyzer. The advantage of s-PBI membranes over Nafion is that conductivity does not decrease at low water content. We have evaluated s-PBI membranes over a range of current densities at 80 and 90°C, and report favorable performance compared to that of Nafion with the possibility of producing higher sulfuric acid concentrations and lower voltages at elevated temperatures.