A versatile Heptazine-COF hybridized ABPBI composite proton exchange membrane with enhanced conductivity and durability for high temperature fuel cell

The leaching of phosphoric acid (PA) from PA-doped polybenzimidazole (PBI) membrane caused by the weak interaction is the origin of its proton conductivity attenuation, which seriously hinders the performance and durability of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). In this study, the Heptazine-COF (Hep-COF) featuring abundant basic C = N units and microporous structure was hybridized with the poly (2,5-benzimidazole) (ABPBI) to fabricate the composite membrane for HT-PEMFC applications. The introduced Hep-COF reinforced acid-base interaction with PA, enhanced the capacity to absorb PA, and simultaneously formed robust and continuous hydrogen bond networks among PA, ABPBI, and Hep-COF, resulting in the enhanced conductivity and PA retention ability of PA-Hep-ABPBI membrane under the HT-PEMFC operation. Furthermore, these hydrogen bond networks additionally contribute to enhanced mechanical properties and chemical stability of the composite membranes. Consequently, the optimized sample 20Hep-ABPBI composite membrane showed a considerable proton conductivity of 105 mS cm − 1 at 180 ℃, enabling a peak power density of 479 mW cm − 2 in single cell test- 2.3 times higher than that of pristine ABPBI membrane. In addition, the PA loss rate (26.95 ng h − 1 cm − 2 ) and voltage degradation rate (25 mV h − 1 ) of the single cell with PA-20Hep-ABPBI membrane were also lower than that of pristine ABPBI membrane after the continuous 120 h operation at 180 ℃. This work offered a valuable strategy for designing and developing a kind of high-performance proton exchange membranes.