Composite Nafion/Sulfated Zirconia Membranes: Effect of the Filler Surface Properties on Proton Transport Characteristics

Abstract

Due to their strong acidity and water affinity, sulfated zirconia nanoparticles were evaluated as inorganic additives in the formation of composite Nafion-based membranes. Two types of sulfated zirconia were obtained according to the preparation experimental conditions. Sulfated zirconia-doped Nafion membranes were prepared by a casting procedure. The properties of the composite membranes were compared with those of an unfilled Nafion membrane obtained by the same preparation method. The water uptake, measured at room temperature in a wide relative humidity range, was higher for the composite membranes, this confirming the hydrophilic nature of the selected additives. The membrane doped by zirconia particles having the highest sulphate group concentration showed the highest water diffusion coefficient in the whole range of temperature and relative humidity investigated due to the presence of SO42− providing extra acid sites for water diffusion. The proton diffusivity calculated from impedance spectroscopy measurements was compared with water self diffusion coefficients measured by NMR Spectroscopy. The difference between proton and water diffusivity became significant only at high humidification levels, highlighting the role of water in the intermolecular proton transfer mechanism. Finally, great improvements were found when using the composite membrane as electrolyte in a fuel cell working at very low relative humidity.

Development of Nafion/Tin Oxide Composite MEA for DMFC Applications

“…It appears then that at such loading the presence of the filler allowed to extend to higher temperatures the stability range of proton conductivity. This finding is in good agreement with previous work on the effect of superacid zirconia on the proton conductivity of Nafion membranes [12,23,25].…”

“…The enlarged stability domain of proton conductivity has been related to the higher stiffness of the composite membranes and thus to their enhanced dimensional stability [20]. The use of acidic fillers, such as heteropolyacids or sulfated metal oxides, has been also explored [21][22][23][24][25]. The acidic surface functionalities of inorganic fillers have been found to play a key role towards the improvement of the water retention properties of the composite membrane and thus of their transport properties.…”

Development of glucose oxidase-based bioanodes for enzyme fuel cell applications

“…To obtain direct electron transfer between the redox center of GOx and electrode surface we have exploited the combination of the excellent properties of carbon nanotubes in terms of dimension, stability and electrical conductivity [8,23,24] with the unique structure and transport properties of Nafion [25,26] as immobilizing matrix. The combined use of spectroscopy and electrochemistry was used as a tool for investigating structure property relationship of the enzyme electrode.…”

On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

“…Many types of inorganic fillers have been reported to decrease the methanol crossover of Nafion membrane. Although some improved electrochemical characteristics have been reported, especially when intrinsically proton conducing fillers have been used, most of the composite membranes have lower proton conductivity than the pure Nafion membrane [9][10][11][12][13][14][15][16][17][18][19].…”