Coconstruction of MOF/CNT-Based Interconnected Acid–Base Pair Hybrid Materials for Improved Performance in Proton Exchange Membranes

UiO-66-NH₂ and UiO-66-SO₃H, which are fine proton conductors, have been extensively applied in the construction of composite proton exchange membranes, owing to their good thermal and chemical stabilities, easy functionalization, and an ideal source of acid-base pairs. In this study, an interconnected acid-base pair hybrid (UNSC, UiO-66-NH₂/-SO₃H-CNTs) was synthesized via the in situ cogrowth of UiO-66-NH₂ and UiO-66-SO₃H on carbon nanotubes (CNTs). The resulting continuous arrays of acid-base pairs promote the formation of ordered proton-transport channels and increase the density of proton-conducting sites, while the CNT-supported hybrid enhances particle dispersion and mechanical strength. Consequently, the achieved SPEEK/UNSC-1 composite membranes exhibited the highest proton conductivity of 39.4 mS/cm at 80 °C, which is 1.5 times higher than that of the recast sulfonated poly-(ether ether ketone) (SPEEK) of 26.1 mS/cm. Besides, the prepared composite membranes also exhibit superior signal cell performance and excellent durability. In direct methanol single-cell tests with 2 M methanol at 80 °C, SPEEK/UNSC-1 exhibited the highest power density of 55.7 mW/cm², which is much higher than that of SPEEK (41.3 mW/cm²). The durability test demonstrated that the composite membranes exhibit good stability in single-cell performance; although operated at 80 °C for 100 h with 2 M methanol, they still maintained an open-circuit voltage higher than 0.6 V.