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

The rare-earth induced polyoxometalate clusters, 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) peroxopolytungstates (peroxo-POTs), have been successfully obtained by a similar synthesis method evolved from that of {P₃W₆(O₂)₆} cluster. But although the original building block in {P₃W₆(O₂)₆} species remained, something completely new was made in the first two examples of peroxo-POTs lanthanide derivatives, which show different structures induced by rare-earth cations. In 2D-Ln₂, [Ln₂(H₂O)₄(OH)P₂W₆(O₂)₄O₂₃]³⁻ is composed of a {P₂W₆(O₂)₄} polyanion unit that are linked by replacing {PW₃(O₂)₃} with {PW₃(O₂)₂}. While rare-earth cations connected with two symmetric {P₂W₃(O₂)₃} cores form 1D-Ln. Furthermore, the proton conductivities of 2D-Ln₂ and 1D-Ln compounds were investigated. Under the condition of 65 oC and 95 % RH, 2D-Pr₂ and 1D-Tb exhibited conductivity of 2.62 × 10⁻³ S cm⁻¹ and 2.78 × 10⁻³ S cm⁻¹, respectively. While the conductivities of their corresponding Nafion membranes were greatly improved and reached 1.65 × 10⁻¹ S cm⁻¹ and 1.44 × 10⁻¹ S cm⁻¹ under the same condition, respectively.