Keeping Superprotonic Conductivity over a Wide Temperature Region via Sulfate Hopping Sites-Decorated Zirconium-Oxo Clusters

Metal-oxo clusters have emerged as advanced proton conductors with well-defined and tunable structures. Nevertheless, the exploitation of metal-oxo clusters with high and stable proton conductivity over a relatively wide temperature range still remains a great challenge. Herein, three sulfate groups decorated zirconium-oxo clusters ( Zr 6 , Zr 18 , and Zr 70 ) as proton conductors are reported, which exhibit ultrahigh bulk proton conductivities of 1.71 × 10 −1 , 2.01 × 10 −2 , and 3.73 × 10 −2 S cm −1 under 70 °C and 98% relative humidity (RH), respectively. Remarkably, Zr 6 and Zr 70 with multiple sulfate groups as proton hopping sites show ultralow activation energies of 0.22 and 0.18 eV, respectively, and stable bulk conductivities of >10 −2 S cm −1 between 30 and 70 °C at 98% RH. Moreover, a time-dependent proton conductivity test reveals that the best performing Zr 6 can maintain high proton conductivity up to 15 h with negligible loss at 70 °C and 98% RH, representing one of the best crystalline cluster-based proton conducting materials.