High temperature proton exchange membranes based on various heteropoly acids (HPW, HSiW, HPMo or HSiMo) functionalized silica nanocomposites with tunable mesoporous structure and superior proton conductivity for fuel cells

摘要

Our recent results on the synthesis and characteristics of high temperature proton exchange membranes based on various heterpoly acids (e.a. phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid) functionalized mesoporous silica nanocomposite were investigated in details for applications in PEMFC and direct methanol fuel cells (DMFCs). The HPA-meso-silica nanocompsoites were characterized by small angle FTIR, TGA, TEM, conductivity and fuel cell performance. Spectroscopy results indicate the interactions between the Keggin anions of HPW (H3PW_(12)O_(40) ·nH2O) and meso-silica and the possible formation of (≡SiOH_2~+)(H2P4W_(12)O_(40)~- ) species. The results show that the proton conductivity of the HPA-meso-silica nanocomposites depends strongly on the content of HPW and exhibits three distinct regions as a function of HPW contents. The threshold for a good proton conductivity of the nanocomposite is ～10 wt%. The best proton conductivity is 0.14 Scm~(-1) at 100 °C under 90 %RH with activation energy of ～13.5 kJ mol~(-1) , obtained on 80%HPW-meso-silica nanocomposites.