Enhancing Proton Conductivity of Nafion Membrane by Incorporating Porous Tb-Metal-Organic Framework Modified with Nitro Groups.

Abstract

A rigid carboxylate ligand with a nitro functional group was selected to coordinate with Tb(III) cation, and Tb-MOF ({[Tb4(L)4(OH)4(H2O)3]·8H2O}n, H2L = 2-nitroterephthalic acid) with large porous and excellent hydrophilicity was obtained successfully. The obtained Tb-MOF was filled into the Nafion matrix to improve its proton conduction performance. The Tb-MOF/Nafion composite membrane was characterized by PXRD, IR, and thermogravimetry (TG) and for water uptake, area swelling, and proton conductivity. The activity energy, Ea, value of the composite membrane, which is a very important factor affecting the proton conduction performance of the membrane, was fitted and calculated. It was revealed that Tb-MOF can improve the proton conductivities of composite membranes, and the improvement degree and Ea value were both affected by Tb-MOF content. When Tb-MOF content was 5%, the proton conductivity of the composite membrane was 1.53 × 10-2 S·cm-1 at 100% RH and 80 °C, which is 1.81 times that of the pure Nafion membrane. A MOF containing a nitro functional group was first doped into Nafion in this study and exhibited excellent performance for improving composite membrane proton conductivity. This study will provide a valuable reference for designing different functionalized MOFs to promote the proton conductivities of proton exchange membranes.