Swift Proton\nRelease Enhancing Proton Conductivity\nin Anderson-Polyoxometalates-Based Metal–Organic Frameworks

Swift proton release in solid-state proton conductors\ncan enhance\nthe proton conductivity. Two new polyoxometalates-based metal–organic\nframeworks (POMOFs), [Cu<sub>2</sub>(HBip)<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>(TeMo<sub>6</sub>O<sub>24</sub>)] (CUST-860) and [Co<sub>3</sub>(Bip)<sub>2</sub>(H<sub>2</sub>O)<sub>10</sub>(TeMo<sub>6</sub>O<sub>24</sub>)] (CUST-861), have been fabricated via combining Anderson-type\nPOMs (TeMo<sub>6</sub>), 3,5-bis(imidazole-1-yl)pyridines (Bips),\nand transition metal ions under hydrothermal method. The related tests\nsuch as powder X-ray diffraction (PXRD) and thermogravimetric analysis\n(TGA) indicated that both compounds exhibit excellent thermal stabilities\nand water stabilities. Alternating current (AC) impedance tests showed\nthat the highest proton conductivity of CUST-861 was 2.96 × 10<sup>–2</sup> S cm<sup>–1</sup> under 90 °C and 98%\nrelative humidity (RH), which is 3 orders of magnitude higher than\nCUST-860. Furthermore, theoretical calculation results indicated that\nthe uncoordinated pyridine nitrogen sites of ligands in CUST-861 have\na lower p<i>K</i><sub>a</sub> value than the uncoordinated\nimidazole nitrogen sites of ligands in CUST-860, which is more conductive\nto proton transfer. This study provides insights into the synthesis\nof solid proton conductors based on POMs.