Proton Conductivity of Proton Exchange Membrane Synergistically Promoted by Different Functionalized Metal–Organic Frameworks

Abstract

In this study, two functionalized metal-organic frameworks (MOFs), UiO-66-SOH and UiO-66-NH, were synthesized. Then, different composite proton exchange membranes (PEMs) were prepared by single doping and codoping of these two MOFs, respectively. It was found that codoping of these two MOFs with suitable sizes was more conducive to the proton conductivity enhancement of the composite PEM. A synergistic effect between these two MOFs led to the the formation of more consecutive hydration channels in the composite PEM. It further greatly promoted the proton conductivity of the composite PEM. The proton conductivity of the codoped PEM reached up to 0.256 S/cm under 90 °C, 95% RH, which was ∼1.17 times higher than that of the recast Nafion (0.118 S/cm). Besides, the methanol permeability of the codoped PEM was prominently decreased owing to the methanol trapping effect of the pores of these two MOFs. Meanwhile, the high water and thermal stabilities of these two MOFs were beneficial to the high proton conductivity stability of the codoped PEM under high humidity and high temperature. The proton conductivity of the codoped PEM was almost unchanged throughout 3000 min of testing under 90 °C, 95% RH. This work provides a valuable reference for designing different functionalized MOFs to synergistically promote the proton conductivities of PEMs.

Improving the performance of sulfonated polymer membrane by using sulfonic acid functionalized hetero‐metallic metal‐organic framework for DMFC applications

“…This may be attributed to the strong interaction between the MOF particles with the polymer backbone. The added MOF particles suppressing the membrane decomposition temperature might be the reason for the enhanced thermal stability …”

“…The product was washed with methanol several times and dried under vacuum. Similarly, Zr‐SO 3 H MOF was synthesized as reported in the literature …”

“…They found that the co‐doping of the two different MOFs in Nafion caused more continuous hydration channels that greatly enhanced the proton conductivity. The co‐doped PEM showed improved methanol resistance due to the trapping ability of MOF pores …”

“…The co-doped PEM showed improved methanol resistance due to the trapping ability of MOF pores. 30 To date, several bi-metallic MOF (or hetero-metallic MOF) were reported for gas adsorption, catalysis, and proton conduction. [31][32][33][34] Integration of two different metals into the framework forms hetero-metallic MOF, which provides the MOF with new functionalities.…”

“…Nevertheless, several protons conducting MOF were used to improve the properties of Nafion and other polymer membranes, [38][39][40] Zirconium (Zr) based MOF (especially UiO-66-SO 3 H) displayed better proton conductivity and stability. 30 The presence of sulfonic acid group on UiO-66-SO 3 H can furnish more proton-conducting channel to the membrane by absorbing water at the interface between the MOF and polymer. 41,42 Based on the above excellent characteristics, in this work, Zr was selected as a primary metal for synthesizing the MOF.…”