Preparation and characterisation of α-layered zirconium phosphate sulfophenylenphosphonates with variable concentration of sulfonic groups

Zirconium phosphate sulfophenylenphosphonates of general formula Zr(HPO4)2−x(SPP)x·nH2O, with SPP = O3PC6H4SO3H and x in the range 0.4–1.35, were precipitated from solutions containing H3PO4, H2SPP and ZrF62−. The SPP/HPO4 ratio in the solids is equal to the H2SPP/H3PO4 ratio in the starting solutions for x ≤ 1 and lower for x > 1. The results coming from 31P MAS NMR, X-ray powder diffraction, FTIR-PAS spectroscopy and density measurements, as well as from the intercalation of α,ω-alkyl diamines in Zr(HPO4)1.00(SPP)1.00, suggest that the solids have a layered structure built up by the packing of symmetric α-layers where SPP and HPO4 groups are uniformly distributed on both layer faces. Proton conductivity, at 100 °C and 70% relative humidity, increases with x and reaches a maximum of 0.04 S cm− 1 for x = 1.35. The conductivity of Zr(HPO4)0.65(SPP)1.35·nH2O was determined as a function of the water content at 100 °C and compared with that of Nafion 117 and of a sulfonated polyetherketone.