Polydopamine-coated polyimide nanofiber to anchor HPW and construct the pocket-like composite membrane with excellent proton conductivity and stability

Solid heteropolyacids with high intrinsic proton conductivity , like phosphotungstic acid (HPW), were added to further enhance the proton conductivity of sulfonated poly ether ketone (SPEEK). The great solubility of solid acid within water, however, would produce a dramatic decline in stability and durability. In this study, we utilized polydopamine (PDA) coated polyimide (PI) nanofiber to form the acid-base pair between PDA@PI nanofiber and HPW/SPEEK to anchor the HPW. Additionally, a pocket was constructed in the sandwich-structure PDA@PI/SPEEK + HPW membrane to help better anchor the HPW. After 6 weeks of durability treatment during 60 °C and 100% RH, proton conductivity of PDA@PI/SPEEK + HPW-20 was 163.5 mS cm −1 , which was only 23.0% lower than that of the initial state . By sharp contrast, it was 55.2% lower than the initial state for pristine SPEEK. And its swelling ratio is only 54% compared with 128% of pristine SPEEK under the same condition. We first revealed and investigated the acid-base pair created by PDA@PI and HPW/SPEEK, which was beneficial for proton conductivity and durability. This pocket-like PDA@PI/SPEEK + HPW membrane would inspire a wide application in PEM among excellent proton conductivity, better stability, with endurance.