Water-Stable\nAl(III)\nCoordination Polymer Glass with\nHigh Proton Conductivity toward Stable Electrolytes in a Fuel Cell

Coordination\npolymer (CP) glasses make up a class of\nsolid-state\nproton conductors as possible electrolytes for anhydrous H<sub>2</sub>/O<sub>2</sub> fuel cells. Toward these potential applications, the\ndevelopment of water-stable CP glasses is crucial to maintaining stable\npower generation over the long-term. Here, we report a water-stable\nAl(III)-based CP glass ((dema)<sub>0.9</sub>[Al(H<sub>2</sub>O)<sub>1.8</sub>(H<sub>2</sub>PO<sub>4</sub>)<sub>3.9</sub>(H<sub>3</sub>PO<sub>4</sub>)<sub>1.1</sub>]). Compared to previously reported\nZn-based CP glasses, the Al-based CP glass showed significantly higher\nhydrolytic stability due to stable coordination bonds. In addition\nto improved water stability, the Al-based CP glass exhibited high\nviscosity (η = 10<sup>1</sup>–10<sup>4</sup> Pa·s)\nand high ionic conductivity (>20 mS·cm<sup>–1</sup> at\n120 °C) under anhydrous conditions. This unique property is attributed\nto a Grotthuss-type selective proton transport mechanism. The H<sub>2</sub>/O<sub>2</sub> fuel cell power generation using this CP glass\nexhibited a high maximum power density (299 mW·cm<sup>–2</sup>) and high open-circuit voltage (0.93 V) under anhydrous conditions\nat 120 °C. These results demonstrate that the employment of Al(III)\nin CP glasses is a promising strategy for the practical application\nof CP glasses in fuel cell devices.