Enhanced Proton Conductivity of an Ionic Hydrogen-Bonded Organic Framework-Embedded Nafion Matrix

Abstract

Herein, we prepared three ionic hydrogen-bonded organic frameworks (iHOFs) of [(La1)·(H2Lb1)·(H2O)2]n (1), [(La1)2·(H2Lb2)·(H2O)2]n (2), and [(La2)·(H2Lb2)·(H2O)]n (3) by organic acid–base reactions (H2La1 = 1,5-naphthalene disulfonic acid, NaHLa2 = monosodium 3-amino-2,7-naphthalenedisulfonate, Lb1 = 3,3′-diaminobenzidine, and Lb2 = 4,4′-diaminodiphenylmethane). There were abundant weak hydrogen bonds and strong ionic bonding interactions between anions and cations in the three iHOF structures, which made them have good thermal stability and high conductivity. An alternating current impedance test showed that the proton conductivity of 1 could reach 1.16 × 10–3 S·cm–1 at 100 °C and 98% relative humidity (RH), and the proton conductivity maximum of 2 and 3 was 1.63 × 10–3 and 3.34 × 10–4 S·cm–1 at 98% RH and 90 °C, respectively. iHOFs had been doped into the Nafion solution, and the hybrid membranes were triumphantly made. The proton conductivity of 6%-1/Nafion and 9%-2/Nafion was calculated to be 2.7 × 10–3 (80 °C) and 1.0 × 10–2 (100 °C) S·cm–1 at 98% RH, which were 2.3- and 6.2-fold higher than that of the original iHOFs, respectively.