An Oxide Ion and Proton Co-Ion Conducting Sn(0.9)In(0.1)P(2)O(7) Electrolyte for Intermediate-Temperature Fuel Cells

The ionic conductivity of Sn(0.9)In(0.1)P(2)O(7) ceramic was investigated under various atmospheres within the temperature range of 130-230 degrees C. Similar to mixed-conductive perovskite oxides at high temperatures (such as SrCe(0.95)Yb(0.05)O(3-alpha,)La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(3-alpha) at 600-1000 degrees C), Sn(0.9)In(0.1)P(2)O(7) can conduct both protons and oxide ions at low temperatures (130-230 degrees C). The conductivity of Sn(0.9)In(0.1)P(2)O(7) reaches 0.019 S/cm at 200 degrees C in wet nitrogen. Its transport numbers determined by steam concentration cells are around 0.76 for a proton and 0.12 for an oxide ion. The performance of direct methanol fuel cells at 170 degrees C using mixed-ion conductive Sn(0.9)In(0.1)P(2)O(7) electrolyte is higher than that at 235 degrees C using pure proton conductive CsH(2)PO(4) electrolyte. This is attributed to direct oxidation of CO at the anode by the oxide ions generated at the cathode and moved through the Sn(0.9)In(0.1)P(2)O(7) electrolyte. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.2988135] All rights reserved.