Investigation on sulfuric acid sulfonation of in-situ sol–gel derived Nafion/SiO2 composite membrane

In this paper, an effective method to cover the conductivity loss of Nafion/SiO2 through sulfonation and its mechanism are studied. Nafion/SiO2 composite membranes are prepared via an in-situ sol–gel route, and then sulfonated with concentrated sulfuric acid (marked as Nafion/S-SiO2). The effects of the sulfonation on properties of the Nafion/SiO2 composite membrane are investigated. The results show that sulfonation can improve the proton conductivity of the Nafion/SiO2 effectively, though it brings water-uptake loss to the composite membrane to some extent simultaneously. According to the results of FT–IR, UV resonance Raman spectroscopy, 29Si solid-state MAS NMR and XRD, it’s proved that higher conductivity of Nafion/S-SiO2 should be relevant to hydrogen bonds & chemical bonds between SiO2 nano particles and sulfuric acid molecules. While, lower water uptake & swelling ratio should be caused by hydroxyl-elimination on the surface of SiO2 nano-particles during sulfonation. Single cell tests show that the performance of Nafion/S-SiO2 composite membranes substantially exceeds Nafion/SiO2 at 110 °C and 59%RH, and in the initial testing stage no performance reduction is observed.