Issues of using inorganic proton conductor in the electrodes of polymer electrolyte fuel cells

Abstract

We clarify the issues to be addressed when inorganic materials are employed in the electrodes of low temperature fuel cells, which conventionally operate around 80 °C. The employed inorganic proton conductor is zirconium sulfophenyl phosphonate (ZrSPP), which is incorporated as an ionomer in the electrode catalyst layers by coating the Pt-supported carbon nanotubes with a ZrSPP layer (ZrSPP–Pt/CNTs). Compared with an MEA with an electrode comprising Nafion and Pt/CNT without a ZrSPP coating, a membrane–electrode assembly (MEA) with an electrode comprising ZrSPP–Pt/CNT exhibits an improved performance at elevated temperatures of 90 °C and 100 °C, illustrating an advantage of the inorganic proton conductors. However, a ZrSPP coating on the Pt/CNTs decreases the cell performance at 80 °C. A detailed in situ analysis using limiting-current measurements reveals that the oxygen transport resistance through the solid ionomers increases by approximately six times with the incorporation of the ZrSPP layer. These results indicate that the mass transport through the inorganic materials should be addressed when they are employed in electrodes. • Issues of using inorganic proton conductors in the electrodes of PEFCs are clarified. • An inorganic proton conductor, ZrSPP, is coated on the surface of Pt/CNTs. • An MEA with ZrSPP-coated Pt/CNTs shows improved performance at 90 °C and 100 °C. • In situ analysis of mass transport properties in the cathode of MEAs is performed. • Oxygen transport resistance through the solid ionomers increases by ZrSPP coating.