Rare-earth-induced peroxo-phosphotungstates: Enhanced proton conductivity in corresponding membranes
Qianqian Shang, Keqin Shen, Dongyan Zhao, Xiaoyue Wang, Yuting Wei, Haiying Wang, Guan Wang, Dongdi Zhang, Jingyang Niu
Abstract
The rare-earth induced polyoxometalate clusters, two-dimensional [Ln<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>(OH)P<sub>2</sub>W<sub>6</sub>(O<sub>2</sub>)<sub>4</sub>O<sub>23</sub>]<sup>3</sup><sup>−</sup> (<strong>2D-Ln<sub>2</sub></strong>, Ln = Pr, Sm) and one-dimensional [Ln(H<sub>2</sub>O)<sub>4</sub>P<sub>4</sub>W<sub>6</sub>(O<sub>2</sub>)<sub>6</sub>(OH)<sub>4</sub>O<sub>24</sub>]<sup>5−</sup> (<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 {P<sub>3</sub>W<sub>6</sub>(O<sub>2</sub>)<sub>6</sub>} cluster. But although the original building block in {P<sub>3</sub>W<sub>6</sub>(O<sub>2</sub>)<sub>6</sub>} 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-Ln<sub>2</sub></strong>, [Ln<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>(OH)P<sub>2</sub>W<sub>6</sub>(O<sub>2</sub>)<sub>4</sub>O<sub>23</sub>]<sup>3</sup><sup>−</sup> is composed of a {P<sub>2</sub>W<sub>6</sub>(O<sub>2</sub>)<sub>4</sub>} polyanion unit that are linked by replacing {PW<sub>3</sub>(O<sub>2</sub>)<sub>3</sub>} with {PW<sub>3</sub>(O<sub>2</sub>)<sub>2</sub>}. While rare-earth cations connected with two symmetric {P<sub>2</sub>W<sub>3</sub>(O<sub>2</sub>)<sub>3</sub>} cores form <strong>1D-Ln</strong>. Furthermore, the proton conductivities of <strong>2D-Ln<sub>2</sub></strong> and <strong>1D-Ln</strong> compounds were investigated. Under the condition of 65 <sup>o</sup>C and 95 % RH, <strong>2D-Pr<sub>2</sub></strong> and <strong>1D-Tb</strong> exhibited conductivity of 2.62 × 10<sup>-3</sup> S cm<sup>-1</sup> and 2.78 × 10<sup>-3</sup> S cm<sup>-1</sup>, respectively. While the conductivities of their corresponding Nafion membranes were greatly improved and reached 1.65 × 10<sup>-1</sup> S cm<sup>-1</sup> and 1.44 × 10<sup>-1</sup> S cm<sup>-1</sup> under the same condition, respectively.