Preparation of Covalent-Ionically Cross-Linked UiO-66-NH2/Sulfonated Aromatic Composite Proton Exchange Membranes With Excellent Performance

Abstract

Metal-organic frameworks (MOFs), as newly emerging filler materials for polyelectrolytes, show many compelling intrinsic features, such as variable structural designability and modifiability of proton conductivity. In this manuscript, UiO-66-NH 2 , a stable MOF with -NH 2 functional groups in its ligands, was selected to achieve a high-performance sulfonated poly(arylene ether nitrile)s (SPENs)/UiO-66-NH 2 -x covalent-ionically cross-linked composite membrane. Simultaneously, the obtained composite membranes displayed excellent thermal stability and dimensional stability. The as-prepared SPEN/UiO-66-NH 2 -x cross-linked membranes exhibited higher proton conductivity than recast SPENs, which can be attributed to the construction of ionic clusters and well-connected ionic nanochannels along the interface between UiO-66-NH 2 -x and SPEN matrix via molecular interactions. Meanwhile, the methanol permeability of the SPEN/UiO-66-NH 2 -x composite membrane had been effectively reduced due to the barrier effect of cross-linking and the addition of UiO-66-NH 2 -x. The SPEN/UiO-66-NH 2 -5 composite membrane had the highest selectivity of 6.42 × 10 5 S·s·cm −3 : 14.3-times higher than that of Nafion 117. The preparation of cross-linked UiO-66-NH 2 /SPEN composite was facile, which provides a new strategy for preparing high performance proton exchange membrane.

High Proton Conductivity of the UiO-66-NH2-SPES Composite Membrane Prepared by Covalent Cross-Linking

“…(2) The interaction between MOFs and SPES limits the chain migration and delayed the disintegration of the polymer chain so that the thermostability of the compound film is enhanced. 29 Water Uptake (WU) and Swelling Ratio (SR) Test. Water absorption is one of the important parameters for the dimension steadiness of the compound film.…”

“…Metal–organic frameworks, new nanoporous materials, , have great development space in many fields due to their high porosity and structural designability − in separation, catalysis, energy, and other advantages. − In recent years, with the rise of proton exchange film, the study of MOFs in proton transport has attracted more and more attention. However, when MOFs are used as proton conduction materials, their own conductivity is poor, and the technology of directly preparing MOFs into membranes is not yet mature, which makes their practical application limited . Polymers with outstanding flexibility and excellent stability are ideal matrices.…”

Enhancing proton conductivity of proton exchange membranes via anchoring imidazole‐loaded MIL‐101‐NH 2 onto sulfonated poly (arylene ether ketone sulfone) by chemical bonding

“…In addition, imidazole molecules inside the channel of Im@MIL‐101‐NH 2 would interact with water molecules, acting as additional proton carriers 53 . Furthermore, the sulfonamide groups formed between Im@MIL‐101‐NH 2 and C‐SPAEKS could devote protons and construct proton transport channels between MOFs and polymers by hydrogen bonding 31,54 . The Im@MIL‐101‐NH 2 could also construct a complete proton transport channel in membranes 55 …”

“…53 Furthermore, the sulfonamide groups formed between Im@MIL-101-NH 2 and C-SPAEKS could devote protons and construct proton transport channels between MOFs and polymers by hydrogen bonding. 31,54 The Im@MIL-101-NH 2 could also construct a complete proton transport channel in membranes. 55 As shown in Figure 11B We proposed the proton transport path for the composite membranes.…”

“…And then these protons transferred on the interface between the Im@MIL-101-NH 2 and C-SPAEKS, which would form a complete proton conduction path from the membrane to the MOFs, and improve the transmission efficiency of protons. 31,33,54,56…”