Rare-earth-induced peroxo-phosphotungstates: Enhanced proton conductivity in corresponding membranes

Two rare-earth-induced peroxo-polyoxotungstates (peroxo-POTs), namely, two-dimensional [Ln₂(H₂O)₄(OH)P₂W₆(O₂)₄O₂₃]³⁻ (2D-Ln₂, Ln = Pr, Sm) and one-dimensional [Ln(H₂O)₄P₄W₆(O₂)₆(OH)₄O₂₄]⁵⁻ (1D-Ln, Ln = Gd, Tb, Dy, Ho), were successfully prepared by similar synthesis methods based on that used to synthesize {P₃W₆(O₂)₆} clusters. However, although the original {P₃W₆(O₂)₆} building block remained, a completely new structure was achieved in these two lanthanide-based peroxo-POT derivatives that was induced by the rare-earth cations. 2D-Ln₂ was composed of {P₂W₆(O₂)₄} polyanion units linked by replacing {PW₃(O₂)₃} with {PW₃(O₂)₂}, while 1D-Ln was composed of two symmetric {P₂W₃(O₂)₃} cores connected by rare-earth cations. Furthermore, the proton conductivities of 2D-Ln₂ and 1D-Ln were investigated. At 65 °C and 95% relative humidity (RH), 2D-Pr₂ and 1D-Tb exhibited conductivities of 2.62 × 10⁻³ and 2.78 × 10⁻³ S∙cm⁻¹, respectively, while the conductivities of their corresponding Nafion membranes were considerably higher, with values of 1.65 × 10⁻¹ and 1.44 × 10⁻¹ S∙cm⁻¹, respectively, under the same conditions.