An Oxide Ion and Proton Co-Ion Conducting Electrolyte for Intermediate-Temperature Fuel Cells

The ionic conductivity of Sn0.9In0.1P2O7 ceramic was investigated under various atmospheres within the temperature range of 130-230oC. Similar to mixed-conductive perovskite oxides at high temperatures (such as SrCe0.95Yb0.05O3-Ą, La0.9Sr0.1Ga0.8Mg0.2O3-Ą at 600-1000oC), Sn0.9In0.1P2O7 can conduct both protons and oxide-ions at low temperatures (130-230oC). The conductivity of Sn0.9In0.1P2O7 reaches 0.019 S/cm at 200oC in wet nitrogen. Its transport numbers determined by steam concentration cells are about 0.8 for proton and 0.1 for oxide-ion. The performance of direct methanol fuel cells at 170oC using mixed-ion conductive Sn0.9In0.1P2O7 electrolyte is higher than that at 235oC using pure proton conductive CsH2PO4 electrolyte. This is attributed to direct oxidation of CO at the anode by the oxide-ions generated at the cathode and moved through the Sn0.9In0.1P2O7 electrolyte.