A new class of proton-conducting polymer was developed via the sol-gel process from amino-containing organic-inorganic hybrids by the treatment of poly (allylamine) with 3-glycidoxypropyltrimethoxysilane doped with ortho-phosphoric acid. The polymer matrix contains many hydrophilic sites and consists of a double-cross-linked framework of polysiloxane and amine/epoxide. Differential scanning calorimetry results suggest that hydrogen bonding or electrostatic forces are present between H3PO4 and the amine nitrogen, resulting in an increase in the glass-transition temperature of the poly(allylamine) chain with an increasing P/N ratio. The 31P magic-angle spinning NMR spectra indicate that three types of phosphate species are involved in the proton conduction, and the motional freedom of H 3PO4 is increased with increasing P/N ratios. The conductivity above 80 °C does not drop off but increases instead. Under a dry atmosphere, a high conductivity of 10-3 S/cm at temperatures up to 130 °C has been achieved. The maximum activation energy obtained at P/N = 0.5 suggests that a transition of proton-conducting behavior exits between Grotthus- and vehicle-type mechanisms. The dependence of conductivity on relative humidity (RH) above 50% is smaller for H3PO 4-doped membranes compared with H3PO4-free ones. These hybrid polymers have characteristics of low water content (23 wt %) and high conductivity (10-2 S/cm at 95% RH), making them promising candidates as electrolytes for fuel cells.
|Number of pages||9|
|Journal||Journal of Polymer Science, Part A: Polymer Chemistry|
|Publication status||Published - 2005 Aug 1|
All Science Journal Classification (ASJC) codes
- Polymers and Plastics
- Organic Chemistry
- Materials Chemistry