Coordinated water molecule-induced solid-state superprotonic conduction by a highly scalable and pH-stable coordination polymer (CP)

The effective design of new efficient crystalline solid-state proton conductors (SSPCs) is relevant to the advancement of clean energy applications. Although it is well known that metal ions enhance the acidity of their coordinated water molecules, proton-conducting coordination polymers (CPs) and metal-organic frameworks (MOFs) in which coordinated water molecules act as sole intrinsic proton sources are largely unexplored. Considering such a design principle, we present a highly scalable and highly robust (stable over a wide pH range of 2-10, in open air for six months, water and boiling water) CP, IITKGP-101, in which Cu-4(mu(3)-OH)(4) SBUs are coordinated with ample water molecules and display superprotonic conductivity in both the single crystal and pellet forms. The 1D chains with hydrophilic interlayer spaces within the framework housing abundant coordinated water as the sole proton source, which make an extended H-bonding pathway for efficient proton migration and thus exhibit a conductivity value of 5.2 x 10(-4) S cm(-1) in single crystal form and 2.45 x 10(-4) S cm(-1) in pellet form at 80 degrees C and 98% RH. The easy scalability in gram scale in an aqueous medium and highly robust nature make this framework a promising candidate as an SSPC.

Automated summary

The effective design of new efficient crystalline solid-state proton conductors (SSPCs) is necessary for clean energy applications. In this study, a coordination polymer (CP), IITKGP-101, is presented as a highly scalable and robust SSPC that exhibits superprotonic conductivity. The CP utilizes coordinated water molecules as the sole intrinsic proton sources, allowing for efficient proton migration and high conductivity values.