One-pot self-assembly synthesis of H3+xPMo12−xVxO40@[Cu6O(TZI)3(H2O)9(NO3)n]·(H2O)15 for enhanced proton conduction materials

Abstract

Due to their strict operating conditions, complicated manufacturing process and unacceptable costs, commercial Nafion-based membranes for fuel batteries are blocked for large-scale applications. Thus, the development of new types of proton conduction materials for fuel cells is impending. Herein, we develop a simple self-assembly solvothermal method to synthesize a series of complexes PMoV_x@rht-MOF-1 (PMoV_x = molybdovanadophosphoric acids, rht-MOF-1 = [Cu₆O(TZI)₃(H₂O)₉(NO₃)]_n·15H₂O) in which a series of PMoV_x are encapsulated in the porous rht-MOF-1 framework. The crystal structures of PMoV_x@rht-MOF-1 have been confirmed by X-ray diffraction analysis. Complexes 1–4 (1, x = 1; 2, x = 3; 3, x = 5; 4, x = 8) are further characterized by FT-IR, TGA, PXRD, SEM analyses and N₂ adsorption–desorption isotherms. The systematic Nyquist experiments reveal that the proton conductivity of complexes 1–4 is dominated by the number of protons in the polyoxometalates (POMs). Strikingly, complex 4 exhibits an outstanding proton conductivity of 8.03 × 10⁻³ S cm⁻¹ at 343 K under 98% RH among the POMs@MOFs composites. Further, the co-relationship between the structures in terms of PMoV_x, water molecules in pore channels and proton conductivity of complexes 1–4 has been investigated. The mechanism of proton conductivity is proposed. This approach provides an easy route to prepare POMs@MOFs, which can effectively prompt the proton conductivity of POMs and prevent the leaching of the POMs in POMs@MOFs.