Enhanced properties of sulfonated polyether ether ketone proton exchange membrane by incorporating carboxylic-contained zeolitic imidazolate frameworks

Abstract

Carboxylic contained zeolitic imidazolate frameworks (ZIF-COOH) were designed and synthesized using 1H-Imidazole-2-carboxylic acid and Zn(NO₃)₂·6H₂O. The ZIF-COOH was then applied in the fabrication of composite membranes with sulfonated polyether ether ketone (SPEEK) (SPEEK/ZIF-COOH). The properties of the composite membranes, including mechanical strength, proton conductivity, and methanol permeability were studied. The incorporation of ZIF-COOH generated a significant effect on SPEEK/ZIF-COOH composite membranes, due to the special structure and compositional characteristics of ZIF-COOH. In particular, the tensile strength of SPEEK/ZIF-COOH-5 showed an enhancement of 44.1 MPa, which was 42% higher than the pristine SPEEK. Simultaneously, the proton conductivity displayed an improvement of 46% as compared to the SPEEK. Most importantly, the methanol permeability values decreased to 1.1 × 10⁻⁷ cm² s⁻¹, which was only a tenth of the value of SPEEK.