Long-Term, Stable Alkaline Electrolysis with a Durable Crystalline Polybenzimidazole Membrane

To overcome the shortcomings of conventional alkaline electrolyzers, polybenzimidazole (PBI) is used to develop novel alkaline electrolysis membranes. In this study, highly crystalline poly(2,2-p-phenylene-5,5-bibenzimidazole) (p-PBI) is synthesized; specifically, the crystallinity of p-PBI is increased during in situ membrane fabrication by introducing an innovative yet simple biaxial stretching step. The biaxially stretched p-PBI (fe-p-PBI) exhibits high crystallinity, which directly affects the electrolytic cell performance. fe-p-PBI is evaluated using platinum-group metal (PGM) and Ni-based catalysts for alkaline electrolysis under various KOH solution feed conditions at different temperatures. The PGM and Ni-based cells exhibit current densities of 4.3 and 0.9 A cm^-2, respectively, at 1.9 V. Further, the electrolysis proceeds without significant damage to the membrane for 900 h at 60 °C. The high crystallinity of fe-p-PBI contributes to the high performance and long-term stability of the alkaline electrolyzer, rendering it suitable for use in practical alkaline water electrolysis applications.