SiO₂/sulfonated poly ether ether ketone (SPEEK) composite nanofiber mat supported proton exchange membranes for fuel cells

A composite membrane of silica (SiO₂)/sulfonated poly (ether ether ketone) (SPEEK) nanofiber mat impregnated with Nafion was fabricated and evaluated for its potential use as a proton conductor for high temperature polymer electrolyte membrane fuel cells. The supporting SiO₂/SPEEK composite nanofibrous skeleton was prepared via electrospinning of a mixture of SPEEK solution and silica sol prepared from tetraethyl orthosilicate (TEOS). The control of hydrolysis and condensation of TEOS enabled to form entangled SiO₂ networks miscible to SPEEK solution. The prepared SiO₂/SPEEK nanofiber mat was impregnated with Nafion^® to completely fill the inter-fiber voids to prepare a dense membrane. The morphology of the nanofiber mat and the composite membrane were observed by scanning electron microscopy and the presence of SiO₂ and SPEEK in the prepared nanofibers was confirmed by FTIR spectroscopy. Proton conductivity and swelling of the membrane were measured. The H₂/O₂ single cell test using the composite membrane as a PEM was performed. At a high temperature and low humidity condition (120 °C and 40 % RH), the maximum power density was 170 mW/cm² for the Nafion-impregnated SiO₂/SPEEK (40/60 w/w) composite nanofiber membrane that was 2.4 times higher than recast Nafion (71 mW/cm²) while SPEEK film failed.