Structure-property relationship analysis of metal-organic frameworks(MOFs) doped proton exchange membrane(PEM)
R. Chen, Jiapeng Li, Pengyu Zhao, Ivan Tolj, Song Li, Zhengkai Tu
Abstract
The introduction of metal-organic frameworks (MOFs) into proton exchange membranes (PEM) to improve their proton conductivity has received growing research interests in recent studies. However, given the enormous number of MOFs, the guidelines to select suitable MOFs for designing high-performing composite membranes are still elusive. In order to reveal the underlying structure-property relationships of composite membranes, a MOFs doped PEM (MOF@PEM) database was established based on the collected proton conductivity of composite membranes from literature in this work. By analyzing the impacts of measurement conditions, MOF loading, water uptake, and MOF modification strategies on the proton conductivity of MOF@PEM, it is found that Grotthuss mechanism plays a dominant role in proton transfer in composite membrane with activation energy below 0.4 eV. The proton conductivities of most MOF@PEM exhibit an initial increase followed by a decrease with MOF loading owing to the disrupted proton transfer channels resulting from MOF aggregation. Besides, although water uptake imposes positive impacts on their proton conductivity, the reduced proton conductivity of specific MOF@PEM at high water uptake demonstrates that other factors such as the spatial distribution of MOF particles and interactions between MOF particles may play critical roles in affecting their proton conductivity. Moreover, chemically or physically modified MOFs as dopants enables the improved proton conductivity of composite membrane owing to the increased proton carriers, reduced tortuosity of proton transfer channels or enhanced water uptake. The current limitations and future perspective for developing high-performance MOF@PEM was proposed in this work.