Reduced magnesium titanate electrodes for solid oxide fuel cells

Abstract

The solid solution series Mg2−yTi1+yO4,0<y<0.5 with average Ti oxidation state, x (3.3<x<3.9), has b een investigated as a possible high temperature anode for fuel cell and electrochemical reactor application. Reduced magnesium titanate spinels, have been shown to have good stability in reducing atmospheres and to resist oxidation in air up to 500°C. Good electronic conductivity is exhibited, with room temperature conductivities in the range 10−4 to 0.5 S cm−1. On increasing temperature, conductivity increases and Arrhenius conductivity dependence is observed, activation energies vary from 50–400 meV from x=3.3 to x=3.9. Thermal expansion coefficients obtained from high temperature powder diffraction studies, ≈1×10−5K−1, demonstrate structural compatibility with 8% yttria-stabilised zirconia electrolytes. Some evidence was found for chemical reaction between (Y2O3)0.08(ZrO2)0.92 and reduced spinel powders at very high temperatures. The product of this reaction was found to be electronic ally conductive; indicating that problems at the electrode/electrolyte interface would not be encountered.