Triazine-rich covalent organic framework composited proton exchange membranes for flexible operating temperature and enhanced long-term stability fuel cells

The high temperature proton exchange membranes (HT-PEMs) possessing both high dimensional stability and excellent proton conductivity is currently a challenge for the development of high temperature proton exchange membrane fuel cells (HT-PEMFCs). The covalent organic frameworks (COFs) are competitive fillers to avoid the above trade-off due to their porous backbone and high specific surface area. In this work, a triazine-rich COF named EB-COF-1 is facilely synthesized at room temperature. Subsequently, a series of COF-doped HT-PEMs are prepared by incorporating varying contents of EB-COF-1 into poly [2,2’-(p-oxydiph-enylene)-5,5′-benzimidazole (OPBI) matrix. The incorporating of EB-COF-1 containing abundant triazine structure can significantly enhance both dimensional and mechanical stability of the hybrid membrane while maintaining its phosphoric acid uptake. Moreover, the EB-COF-1 can promote the establishment of dense hydrogen bonds network within membrane and improve its proton conductivity. Among them, the membrane containing 7 wt% EB-COF-1 exhibits highest peak power density (236.45 mW cm −2 at 80 °C and 768.41 mW cm −2 at 180 °C, under anhydrous conditions) over a flexible operating temperature range as well as an excellent proton conductivity of 0.1799 S cm −1 at 180 °C. Moreover, its voltage decay rate (0.069 mV h −1 ) is only 14.22 % of OPBI after 150 h long-term stability test.