Proton Conducting Self-Assembled Metal–Organic Framework/Polyelectrolyte Hollow Hybrid Nanostructures

Abstract

Herein, a room temperature chemical process to synthesize functional, hollow nanostructures from zeolitic imidazolate framework-8 (ZIF-8) and poly(vinylphosphonic acid) (PVPA) is reported. Syntheses are initiated by physically blending the components-a process that is accompanied first by encapsulation of ZIF-8 crystallites by PVPA and then by fragmentation of the crystallites. The fragmentation process is driven by partial displacement of the methyl-imidazolate ligands of Zn(II) in ZIF-8 by phosphonate groups on PVPA. Differences in rates of diffusion for the components of the reactive mixture yield a Kirkendall-like effect that is expressed as a hollow-particle morphology. The obtained hollow nanostructures feature hybrid shells containing PVPA, ZIF-8, and their cross-reacted products. The hybrid structures display substantial proton conductivities that increase with increasing temperature, even under the anhydrous conditions prevailing at temperatures above the boiling point of water. For example, at T = 413 K the proton conductivity of ZIF-8@PVPA reaches 3.2 (±0.12) × 10(-3) S cm(-1), a value comparatively higher than that for PVPA (or ZIF-8) in isolation. The high value may reflect the availability in the hybrid structures of free (and partially free), amphoteric imidazole species, and their hydrogen-bonding interactions with phosphonate and/or phosphonic acid units. The persistence of ample conductivity at high temperature reflects the elimination of phosphonic acid group dehydration and dimerization-an effect that strikingly degrades the conductivity of pure PVPA under anhydrous conditions.

Proton Conductivity of Composite Polyelectrolyte Membranes with Metal‐Organic Frameworks for Fuel Cell Applications

“…In a later study, these researchers reported on the room temperature synthesis of functional hollow nanostructures composed of poly(vinylphosphonic acid) (PVPA) and ZIF‐8 . For that, hollow hybrid nanostructures were fabricated by physical blending methods at room temperature, which possessed lower accessible surface areas that ZIF‐8 nanoparticles, due to the blocking of ZIF‐8 pores by the PVPA polymer.…”

“…A) Chemical structure of PVPA polymer. B) Plot of proton conductivity at different temperatures of PVPA@ZIF8 hollow nanostructures under anhydrous conditions …”

Significant Enhancement of Proton Transport in Bioinspired Peptide Fibrils by Single Acidic or Basic Amino Acid Mutation

“…Ceramic materials, as well as polymers, have been extensively studied for these applications. Furthermore, new types of materials including zeolites, solid acids, graphene oxide, carbon nanotubes, covalent organic frameworks, and metal organic frameworks (MOFs) have also demonstrated promising proton transport characteristics. Lately, a new porous bioinspired MOF (bioMOFs) design was reported to be a good proton conductor alternative as well .…”

Advances in Metal−Organic Ligand Systems for Polymer Electrolyte Membranes: A Review

“…These types of compounds display proton conductivities which increase with increasing temperature under anhydrous conditions, which may be the result of hydrogen bonding. A schematic representation is given in Figure . The reported results of Zn‐aminotriazolato‐oxalate and a sulfonated poly(phthalazinone ether sulfone ketone) compound showed enhanced proton conductivity and low permeability as compared to Nafion .…”

“…(b) Potential mechanism for proton transfer in zeolite imidazolate frameworks and PVPA hollow nanostructures. (Reprinted with the permission of ACS . )…”