Proton Conduction of a Hydrothermally Synthesized Hexaazatriphenylene‐Based Covalent Organic Framework

Abstract Recently, hexaazatriphenylene (HA)‐based covalent organic frameworks have garnered attention as polymer electrolyte membranes (PEMs) in polymer electrolyte fuel cells due to their robust framework and strong ion‐trapping capabilities. In this study, quinone‐functionalized HA‐based covalent organic frameworks (HAQ‐COFs) are synthesized by hydrothermal synthesis. This method is much simpler than the synthesis methods previously reported, and is also suitable for mass production. X‐ray diffraction (XRD) and Fourier‐transform infrared measurements reveal that HAQ‐COF exhibits a crystal structure where 2D molecular layers, formed by HA units and bridging paraquinone units, are stacked, creating pores that align to form channels for ion transport. Thermogravimetry and XRD measurements, as a function of temperature, demonstrate that HAQ‐COF exhibits high water retention capacity at room temperature and atmospheric pressure and has greater thermal stability than other PEMs. Electrochemical impedance spectroscopy measurements indicate that the proton conductivity of HAQ‐COF remains nearly unaffected by changes in external humidity, allowing it to sustain high proton conductivity even under sudden humidity drops. Moreover, the activation energy for proton hopping conduction in HAQ‐COF is significantly lower compared to that of similar proton conductors.