Hybrid materials based on the Nafion membrane and acid salts of heteropoly acids MxH3 – xPW12O40 and MxH4 – xSiW12O40 (M = Rb and Cs)

Abstract

The effect of the modification of Nafion membranes with nanoparticles of acid salts of heteropoly acids has been described. Ion conductivity at high and low relative humidity (RH), diffusion permeability, and mechanical properties of hybrid materials have been studied. It has been shown that the membrane modification with the acid salts of heteropoly acids makes it possible to increase the ionic conductivity both at high and low humidity, with the conductivity being determined by the amount of charge carriers at the surface of the dopant particles. The most significant effect of dopant incorporation is observed at low humidity. The conductivity of the sample Nafion + 5 wt % of Cs_xH_{4 – x}SiW₁₂O₄₀ at room temperature is σ = 4.1 mS/cm and it is more than two times as high as the conductivity of the initial Nafion membrane at RH = 30%. By modifying with the acid salts of heteropoly acids, the diffusion permeability of the hybrid membranes is reduced as compared to the initial membrane, thereby suggesting an increase in cation transport selectivity along with an increase in proton conductivity. Introduction of small amounts of the dopant do not cause deterioration of the mechanical properties of the membrane.