title: 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.
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Unal
authors.initials: U
authors.lastname: Sen
authors.forename: Mustafa
authors.initials: M
authors.lastname: Erkartal
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.|Department of Chemical Engineering, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Chung-Wei
authors.initials: CW
authors.lastname: Kung
authors.affiliation: Center for Electrochemical Science and Engineering, Department of Chemical and Biological Engineering, Illinois Institute of Technology , 10 West 33rd Street, Chicago, Illinois 60616, United States.
authors.forename: Vijay
authors.initials: V
authors.lastname: Ramani
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Hupp
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.|Department of Chemistry, Faculty of Science, King Abdulaziz University , Jeddah, Saudi Arabia.
authors.forename: Omar K
authors.initials: OK
authors.lastname: Farha
keywords: PVPA; ZIF-8; fuel cell; hollow nanostructures; proton conductivity