Intermediate-Temperature Anhydrous High Proton Conductivity Triggered by Dynamic Molecular Migration in Trinuclear Cluster Lattice

Summary

Building an efficient and uninterrupted hydrogen-bond network by visualized crystal-structure phase transformation to improve anhydrous proton conductivity and to elucidate the proton-transfer mechanism is desirable but rare. Here, we have discovered a proton conductivity "hysteresis" phenomenon triggered by an obvious structural transformation in which the dynamic molecular migration in a trinuclear cluster (NNU-66) results in the reorganization of the H-bond network. The cluster structure after transformation (NNU-66a) exhibits a remarkable proton conductivity of 1.94 × 10⁻³ S cm⁻¹ and a superior performance durability of 24 h at 180°C. The peculiar "SCN⁻ passageway" in NNU-66a plays a vital role in building an effective hydrogen-bond network for fast proton transfer. Moreover, the corresponding density functional theory results indicate that the introduction of the SCN⁻ passageway dramatically lowers the energy required for proton hopping. Additionally, NNU-66a is further fabricated into a proton-exchange membrane and used in H₂/O₂ fuel cells.