Water-Stable Al(III) Coordination Polymer Glass with High Proton Conductivity toward Stable Electrolytes in a Fuel Cell

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