Facilitating the proton conductivity of polyvinyl alcohol based proton exchange membrane by phytic acid encapsulated Zn-azolate MOF

Abstract

It is important but still challenging to develop high-performance proton exchange membranes (PEMs) which should meet the following requirements: consecutive proton-conducting channels, efficient proton transfer, and excellent stability. In this study, polyvinyl alcohol (PVA) composite membranes were constructed by loading post synthetically phytic acid (PA) encapsulated Zn-MOF, denoted as PVA@PA@Zn-MOF-X (X = 0, 2, 4, 6. wt%). The novel Zn-MOF with high thermal and pH stability has been synthesized from the zinc salt and dual ligands (H2NDI: 2,7-bis(3,5-dimethyl) dipyrazol-1,4,5,8-naphthalene-tetracarboxydiimide; HBTA: 1 H-benzotriazole) which can be employed to host PA as proton carriers. Composite membranes were evaluated by microstructure, thermal stability, mechanical property, dimensional stability, proton conductivity, and so forth. It is found that the codoping of PA encapsulated Zn-MOF with suitable content is more stability of the composite membranes. Furthermore, PVA@PA@Zn-MOF-4 shows the highest proton conductivity of 1.85 × 10-2 S cm-1 at 80 oC and 90% RH with relatively lower value for ion exchange capacity (0.58 mmol g-1) among the composite membranes. This phenomenon is attributed to the consecutive hydrogen bonding networks which are composed of the carbonyl oxygen sites within Zn-MOF, phosphate groups of PA, and hydroxyl groups of PVA, enhancing the efficiency of proton transport. This is a referable strategy for designing and constructing the high-performance PEMs for fuel cells.