Abstract
Substitutional solid solutions based on polyantimonic acid H2Sb2 – xNbxO6·nH2O \(\left( {n \geqslant 1} \right)\) and their composites H2Sb2 – xNbxO6·0.5yNb2O5 nH2O \(\left( {n \geqslant 1} \right)\) the promising components for low-temperature fuel cell membranes, are synthesized by coprecipitation. The Nb5+ ions which have the similar radius and electronegativity as the Sb5+ ions are used as the dopant. The elemental composition of samples (the Nb5+/Sb5+ ratio) is refined using X-ray fluorescence analysis. The solid solution composition, limiting as regards the dopant concentration, i.e., H2Sb1.6Nb0.4O6·nH2O ions increase the lattice parameter for the samples with 0 < x ≤ 0.4. By analyzing the dielectric properties and the protonic conductivity of samples at a temperature of 25°C and a relative humidity of 58%, it is shown that the sample with x = 0.6 has the best transport properties. Its protonic conductivity is 11.5 × 10–3 S/m. The protonic conductivity of polyantimonic acid and the solid solution with the limiting dopant concentration (x = 0.4) is 7.2 × 10–3 and 5.0 × 10–3 S/m, respectively. A possible mechanism of protonic conduction is proposed, namely, the correlated proton transport along a certain chain of hydrogen bonds through channels in the pyrochlore structure and through the intergranular space that contains adsorbed water and niobic acid.
