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⁻ (<strong>2D-Ln₂</strong>, Ln = Pr, Sm) and one-dimensional [Ln(H₂O)₄P₄W₆(O₂)₆(OH)₄O₂₄]⁵⁻ (<strong>1D-Ln</strong>, 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 <strong>2D-Ln₂</strong>, [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 <strong>1D-Ln</strong>. Furthermore, the proton conductivities of <strong>2D-Ln₂</strong> and <strong>1D-Ln</strong> compounds were investigated. Under the condition of 65 ^oC and 95 % RH, <strong>2D-Pr₂</strong> and <strong>1D-Tb</strong> 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.