Proton Conduction of Nafion Hybrid Membranes Promoted by NH₃-Modified Zn-MOF with Host–Guest Collaborative Hydrogen Bonds for H₂/O₂ Fuel Cell Applications

Abstract

It is of great significance to develop creative proton exchange membrane materials for proton exchange membrane fuel cells (PEMFCs). The strategy of doping metal-organic frameworks (MOFs) with guest molecules into the Nafion matrix is adopted to improve the electrochemical performance of Nafion hybrid membranes. Various and abundant hydrogen bonds can make a tremendous contribution to the proton conduction of hybrid membranes. In this work, we used high proton-conducting Zn-MOFs with the characteristics of host-guest collaborative hydrogen bonds as the filler to prepare Zn-MOF/Nafion hybrid membranes. Alternating current (AC) impedance tests show that when the doping amount of Zn-MOF is 5%, the proton conductivity reaches 7.29 × 10^-3 S·cm^-1, being 1.87 times that of the pure Nafion membrane at 58% relative humidity (RH) and 80 °C. In an attempt to prove the promotion effect of guest NH₃ on proton conductivity of Nafion hybrid membranes, Zn-MOF-NH₃ was filled into the Nafion matrix. Under the same conditions, its proton conductivity reaches the maximum value of 2.13 × 10^-2 S·cm^-1, which is 5.47 times that of the pure Nafion membrane. Zn-MOF-NH₃/Nafion-5 was used to fabricate a proton exchange membrane for application in H₂/O₂ fuel cells. The maximum power density of 212 mW cm^-2 and a current density of 630 mA cm^-2 reveal a respectable single cell performance. This study provides a promising method for optimizing the structure of MOF proton conductors and inspires the preparation of high-performance Nafion hybrid membranes.