Constructing Denser Hydrogen-Bonding Networks in Polyoxometalate-Based Coordination Polymers for Enhancing Proton Conduction

It is urgent and significant to design and fabricate long-range ordered crystalline proton-conductive materials and study their proton conduction mechanisms. Two new polyoxometalate-based coordination polymers, named CUST-963 and CUST-964, have been constructed by combining Keggin-type H₄SiW₁₂O₄₀ (SiW₁₂), nitrogen-rich ligand 2,5-di(1<i>H</i>-imidazole-1-yl)terephthalic acid (H₂DTA), and transition metal ions under hydrothermal conditions. X-ray diffraction analysis revealed that there are more uncoordinated nitrogen sites within CUST-963, which can collaboratively form a denser and continuous hydrogen-bonding network with surface oxygen atoms of SiW₁₂ and water molecules and act as proton hopping sites. The alternating current impedance tests suggested CUST-963 achieves a lower activation energy (0.14 eV) and a higher proton conductivity (1.88 × 10^-2 S cm^-1) than that of CUST-964 under 95 °C and 98% relative humidity. This work provided an effective strategy for designing high-performance proton-conductive materials.