Studies of heteropoly acid/polyvinylidenedifluoride–hexafluoroproylene composite membranes and implication for the use of heteropoly acids as the proton conducting component in a fuel cell membrane

Complete polarization curves for a number of heteropoly acids (HPAs), H₃PW₁₂O₄₀, α-H₃P₂W₁₈O₆₂, H₆P₂W₂₁O₇₁, and H₆As₂W₂₁O₆₉ as the only proton conducting component are presented for the first time. Both thin pellets of HPA and composite membranes of 1:1 (w/w) of HPA and polyvinylidenedifluoride–hexafluoropropylene (PVDF–HFP) are investigated. Although the pellets are somewhat variable, the HPA phase changes can be observed by electrochemistry and these materials show promise for solid acid fuel cell performance at >200 °C. The high proton conductivities reported for HPAs at RT are demonstrated in fuel cells using HPA/PVDF–HFP composites with limiting current densities as high as 1.6 A cm⁻² using dry O₂ and H₂. Moderate fuel cell activity is demonstrated for α-H₃PW₁₈O₆₂ at 120 °C and 25%RH. Unfortunately all of the materials studied were somewhat porous and the open circuit potentials observed were somewhat low. We were also able to show that an HPA fuel cell could be shorted by reduction of the HPA to a heteropoly blue under exceptional circumstances.