Influence of activated protons and acid–base pairs on proton conduction in imino-functionalized MOF-based hybrid membranes

Abstract

The rich activated protons and effective proton-conducting paths are of importance to improve conductivities of conductors. Herein, a series of Brönsted acids as proton carrier and proton transfer sites is introduced into the highly stable MOF, contributing to create plentiful hydrogen bonds within frameworks. Consequently, the trifluoromethanesulfonic acid-embedded JUC-1000 ([Cu24(BDPO)12(H2O)12]) displays the relatively highest conductivity of 7.04 × 10−4 S cm−1 under ∼98% RH and 328 K, ∼16 times that of JUC-1000 (4.47 × 10−5 S cm−1). When TMSA@JUC-1000 (TMSA = CF3SO3H) blended with chitosan (CS), the proton conductivity of TMSA@JUC-1000/CS-15 is the highest at ∼76% RH and 328 K (1.01×10−2 S cm−1), which is six times higher than that of JUC-1000/CS (1.85×10−3 S cm−1). The CS contains abundant –NH2 and –OH groups as proton jumping sites, which would activate the –NH– or –OH bonds of JUC-1000 and the acidic groups in Brönsted acids. These would result in an increased content of activated protons and effective formation of H-bonding nets by acid-base interactions. The findings provide valuable insights into the potential application of MOFs materials in energy devices.