Preparation and Electrochemical Performance of Tungstovanadophosphoric Heteropoly Acid and Its Hybrid Materials

Tungstovanadophosphoric heteropoly acid H6PW9V3O40·(13.81 ± 0.13)H2O (abbreviated as PW9V3) has been synthesized by the stepwise acidification and the stepwise addition of element solutions. The crystal structure was determined from single crystal X-ray diffraction. The complex crystallizes in the space group R3̅m, with a = 16.4374 (9) Å, b = 16.4374 (9) Å, c = 25.3866 (14) Å, α = 90°, β = 90°, γ = 120°, V = 5940.20 Å, and Z = 6. The product possesses Keggin structure, and its conductivity was 1.730 × 10–2 S·cm–1 at 26 °C and 75% relative humidity by electrochemical impedance spectroscopy (EIS) measurement. Two conducting systems were prepared with a mixture of as-synthesized PW9V3 and organic polymers [polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG)] at the weight ratio 80:20. The hybrid materials exhibit high proton conductivities with 7.110 × 10–3 and 1.050 × 10–2 S·cm–1 (PW9V3/PEG) at 26 °C and 75% relative humidity, respectively. Their activation energies of proton conduction are 15.23 and 13.67 kJ·mol–1, which are lower than that of pristine heteropoly acid (25.68 kJ·mol–1). Their mechanisms of proton conduction are also proposed.