Hydrothermal Synthesis, Structure, and Electrochemical Properties of a Three-dimensional Vanadium-Nickel Phosphate (C2H10N2)4[H2Ni(H2O)2(VO)8(OH)4(PO4)8]·H2O

Synthesis of Phosphovanadate-Based Porous Inorganic Frameworks with High Proton Conductivity

Materials with high proton conductivity have attracted significant attention for their wide-ranging applications in proton exchange membrane fuel cells. However, the design of new and efficient porous proton-conducting materials remains a challenging task. The structure-controllable and highly stable metal phosphates can be synthesized into layer or frame networks to provide proton transport capabilities. Herein, we have successfully synthesized three isomorphic metal phosphovanadates, namely, H2(C2H10N2)2[MII(H2O)2(VIVO)8(OH)4(PO4)4(HPO4)4] (C2H8N2 = 1,2-ethylenediamine; M = Co, Ni, and Cu), by the hydrothermal method employing ethylenediamine as a template. These pure inorganic open frameworks exhibit a cavity width ranging from 6.4 to 7.5 Å. Remarkably, the proton conductivity of compounds 1-3 can reach 1 × 10-2 S·cm-1 at 85 °C and 97% relative humidity (RH), and they can remain stable at high temperatures as well as long-term stability. This work provides a novel strategy for the development and design of porous proton-conducting materials.