Rational Tuning the Proton Conductivity and Stability\nof Hydrogen-Bonded Organic Frameworks

In\nthe development of proton conductors, it is crucial to regulate\nproton conduction pathways and enhance structural stability. In this\nstudy, we designed and constructed three hydrogen-bonded organic frameworks\n(HOFs), namely, NKM-HOF-9, NKM-HOF-10, and NKM-HOF-11, with different\ndimensional hydrogen-bonding pathways using 4,4′-sulfonyldibenzoic\nacid and various bases. They are cost-effective and easy to synthesize,\nallowing for their large-scale production at room temperature. By\npurposefully altering the ammonium ions, we achieved enhancements\nin the conductivity and stability of these HOFs. Proton conductivity\nstudies at different humidities and temperatures revealed that at\n85 °C and 98% relative humidity, the proton conductivity of NKM-HOF-10\nreached 1.7 × 10<sup>–3</sup> S cm<sup>–1</sup>, surpassing that of NKM-HOF-9 by 1 order of magnitude. This improvement\nwas accomplished by increasing the number of proton donors from the\nbase, which resulted in a transition of the hydrogen bond network\nfrom discontinuous to continuous, thereby enhancing the proton conduction\nperformance. Moreover, stability tests showed that raising the base’s\np<i>K</i><sub>a</sub> could improve the stability of these\nframeworks. NKM-HOF-11, which features the highest p<i>K</i><sub>a</sub>, demonstrated superior stability by maintaining its\nstructural integrity even at 450 °C.