Conductivity and Transport Properties of Aqueous Phosphotungstic and Silicotungstic Acid Electrolytes for Room-Temperature Fuel Cells

Conductivity measurements were performed on phosphotungstic and silicotungstic aqueous electrolyte solutions. The conductivity obtained from complex impedance plots had non-Arrhenius dependence on temperature and could be fit by the Vogel-Tamman-Fulcher expression, T1/2exp[Qc/(T­To)]. Conductivities reached 0.257 and 0.32Scm−1 at 298 K for the 60 wt % phosphotungstic and silicotungstic solutions, respectively. Low concentration silicotungstic solutions obeyed the Kohlrausch relation allowing for the determination of infinite dilution molar conductivity, 1637Scm2 mol−1, with the anionic species 14[SiW12O40]4− having a molar conductivity of 237Scm2 mol−1. The diffusion coefficient of the anionic species at 303 K was 4.8×10−6 cm2 s−1 with a hydrodynamic radius of 5.78 Å. Analysis of the charge transference numbers indicated that the conductivity was predominantly protonic, and suitable for room-temperature fuel cells. © 2003 The Electrochemical Society. All rights reserved.