Confining Macrocyclic Molecules into a Porous Metal-Organic Framework for Enhanced Proton Conduction

Given the critical need for high-performance proton-exchange materials in clean energy devices, design and synthesis of composite materials based on metal-organic frameworks (MOFs) has emerged as a highly promising strategy due to their unique porosities, tunable functionalities, and high surface areas. Herein, functional macrocyclic molecules (Cucurbit[6]uril, CB[6]) were entrapped into the pore channels of the MIL-101(Cr) MOFs through an encapsulation strategy. By regulating the synthesis conditions, a series of composite materials with varying loading amounts of CB[6] were successfully synthesized, denoted as CB[6]@MIL-W%, where W represents the mass percentage of CB[6] incorporated (W = 18, 26, or 30). Their proton conduction behaviors have been investigated. Among various CB[6]@MIL-W%, the CB[6]@MIL-26% exhibited a higher proton conductivity of 8.54 × 10^-3 S cm^-1 at 95 °C and 98% relative humidity (RH), surpassing that of MIL-101 by five times which is due to the encapsulated CB[6] molecules could form a denser and more continuous hydrogen-bonding network in the pores of MIL-101, effectively enhancing the proton conductivity of composite material. This work opens a new pathway for enhancing proton conductivities of MOFs through a host-guest strategy.