Study on the PI/SPEEK nanofiber composite proton exchange membrane for fuel cells

Sulfonated poly ether ether ketone (SPEEK) can be selected as the candidate for proton exchange membrane (PEM) used in the fuel cell for its cheap price, great proton conductivity and stability. To further improve its performance, more SO₃H were induced into SPEEK but would result in excessive swelling and losing its stability. Polyimide (PI) nanofibers have excellent mechanical properties and can be a supporter to improve stability. In this work, the PI nanofiber was put in the middle of the SPEEK to create the PI/SPEEK nanofiber composite membranes (NCMs). Its morphology of PI/SPEEK NCMs observed by SEM showed that PI nanofiber was almost in the middle of these NCMs. The proton conductivity and swelling ratio of 3%PI/SPEEK were 271.7 mScm^-1 and 20.0% at 60°C and 100% RH, which is 29.6% higher and 90.4% lower than that of pristine SPEEK. It was intact after the single-cell test in the fuel cell and its power density was 199.1 mWcm^-2, but for pure SPEEK there was some broken area on it. The reason was that PI/SPEEK can maintain the durability of the channels for the proton to transport and it can be attributed to an interaction at their interface of PI nanofiber and SPEEK. The 3%PI/SPEEK NCM will have a broad application prospect in PEM fuel cells.