Phosphoric Acid Electrolyte Uptake and Retention Analysis on UiO-66-NH₂ Polybenzimidazole Nanocomposite Membranes

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) have a major advantage over low-temperature fuel cells due to their better tolerance to higher carbon monoxide content in the hydrogen feed, simpler fuel processing, and better heat management. However, a key challenge in the development of HT-PEMFCs is the potential for acid leaching from phosphoric acid-doped polybenzimidazole membranes, which can reduce overall fuel cell performance. This study investigates the effect of post-synthetic modification of the UiO-66-NH₂ metal–organic framework (MOF) on the acid electrolyte uptake and retention of MOF/poly(4,4ʹ-diphenylether-5,5ʹ-bibenzimidazole) (OPBI) nanocomposite membranes. Thermogravimetric analysis (TGA) was used to correlate the membrane properties with acid uptake. This work revealed that the presence of MOF with functional groups that can form hydrogen bonds with phosphoric acid molecules was able to alleviate the acid retention in the OPBI membrane with lower acid uptake. TGA demonstrated that the lower bound moisture content in the nanocomposite membranes was correlated to the lower acid uptake. In addition, the thermal stability of the nanocomposite membranes was found to improve.