A class of phosphonic acid-grafted hybrid inorganic-organic polymer membranes was synthesized using a sol-gel process. Their thermal stability, water uptake, and proton conductivity were investigated. TGA-DSC analysis indicated that these membranes are thermally stable up to at least 220 uC in dry air. The proton conductivities of the new membranes increase with -PO 3 H 2 group content and relative humidity, reaching 6.2 6 10 22 S cm 21 at 100 uC with y100% relative humidity, comparable to those of Nafion 1 under similar conditions. These new membranes have high proton conductivity at low relative humidity and thus have great potential to be used as electrolytes for high-temperature, low-humidity PEM fuel cells and other electrochemical applications. The proton conductivity of the membranes in the anhydrous state was enhanced by substitution of -CH 2 -PO 3 H 2 groups with -CF 2 -PO 3 H 2 groups owing to the large electronwithdrawing effect of C-F bonds. However, it was found that the concentration of -PO 3 H 2 groups and the molecular structures of the new membranes are the key factors for the proton transport process in a humidified environment.

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Non‐fluorinated sulphonated polyphosphazene (SPOP) was synthesised and characterised for utilisation as an electrode binder. Polarisation curves were obtained at 80 °C and 95% RH in a H2/air fuel cell. SPOP has the proper properties for a cathode binder in a fuel cell, as its polarisation curve traced that of Nafion® binder for the same operating conditions.

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High-density acid model electrolyte was synthesized by sol-gel method and the effect of acid density on proton conductivity was investigated. Model electrolyte showed high proton conductivity (over 0.01 S/cm) at high temperature and low humidity (120 °C, below 1 %RH). In model electrolyte, dense ion channel was formed and proton conduction by grotthuss mechanism became dominance than that by vehicle mechanism at low relative humidity.