Highly proton conductive and mechanically robust SPEEK composite membranes incorporated with hierarchical metal–organic framework/carbon nanotubes compound

Abstract

The preparation of composite proton exchange membranes (PEMs) by incorporating metal- organic frameworks (MOFs) into polymeric substrates has become a hot research topic in the field of fuel cells in recent years. In this work, ZSC was prepared by in-suit reacted with the precursor of ZIF-8 (Zeolitic Imidazolate Framework 8) and silica coated carbon nanotubes (SiO2@CNTs). The as-prepared ZSC was introduced into sulfonated poly (ether ether ketone) (SPEEK) to fabricate a series of composite proton exchange membranes SPEEK/ZSC-x (where x is the mass percentage between ZSC and SPEEK). The coating treatment of carbon nanotubes (CNTs) by silica not only can avoid the direct contacting among CNTs and enhance the dispersion in SPEEK matrix, but also realize the regulation of nucleation and crystallization process of ZIF-8 particles along the morphology of CNTs. The obtained SPEEK/ZSC composite membranes show improved performance owing to construction of interconnected network architecture and the compositional advantages of the ZSC materials. The proton conductivity of SPEEK/ZSC-0.5 membrane was up to 38.10 mS/cm at 80 °C, which was 1.8 times that of the pure SPEEK membrane (21.12 mS/cm) under the same condition. Moreover, the SPEEK/ZSC-0.5 showed better performance with peak power density of 38.9 mW/cm2 in 2 M methanol solution, which was 1.3 times that of the pure SPEEK membrane of 30.3 mW/cm2, the further stability tests confirmed that the composite film maintained good voltage stability even after 100 h of continuous operation at 80 °C. These results indicate that the strategy of construction MOFs and functional CNTs hybrid materials show promising application prospects in the preparation of high performance PEMs.

Keywords

• ZIF-8
• Carbon nanotubes
• Sulfonated poly (ether ether ketone)
• Composite membranes
• Proton conductivity