Persistent Superprotonic Conductivity in the Order of 10(-1) S.cm(-1) Achieved Through Thermally Induced Structural Transformation of a Uranyl Coordination Polymer

Despite tremendous efforts being made in the exploration of new high-performance proton-conducting materials, studies on systems with superprotonic conductivity higher than 10(-1)S.cm(-1) remain scarce. Herein, we utilize bridging uranyl oxo atoms, traditionally termed cation-cation interaction (CCI), as the hydrogen bond acceptor to build a dense and ordered hydrogen bond network that leads to the formation of a unique uranyl-based proton-conducting coordination polymer, HUP-1, (H3O)(4)UO2(PO4)(2). This compound contains a densely connected hydronium network that is stabilized by uranyl oxo atoms and exhibits high proton conductivities over a wide temperature range. At 98 degrees C and 98% relative humidity, a superprotonic conductivity of 1.02 x 10(-1) S.cm(-1) is observed for the system, resulting in one of the highest values reported for a solid-state proton-conducting material. This property originates from the thermally induced phase transformation from HUP-1 to HUP-2, (H3O)UO2PO4 center dot(H2O)(3), another uranyl compound which also contains a CCI bond, and is accompanied by the partial generation of phosphoric acid. The phosphoric acid is further trapped in the structure of HUP-2, as is demonstrated by solid-state NMR analysis. The superprotonic conductivity of H3PO4@HUP-2 persisted under the testing conditions used. [GRAPHICS] .