New Cathode Catalyst for Room Temperature Carbonate Fuel Cells

Synthesis of calcium ruthenate pyrochlores was performed using a hydrothermal route. The resulting material was physically characterized by x-ray diffraction, BET gas adsorption and scanning electron microscopy. The use of low concentration KMnO4 (10mM) in the hydrothermal synthesis, in combination with high pH (similar to 14) and moderate temperature (200 degrees C), yielded a highly crystalline, thermally stable Ca2Ru2O7-y pyrochlore. Micron-sized primary particles with a high density of surface nanocrystallites were obtained. The presence of the nanocrystallites gave the pyrochlore a high surface area, 174 m(2)/g. Thin-film disk electrode experiments showed a slight increase in the kinetic current for O-2/CO2 reduction, compared to O-2-only reduction. Fuel cell experiments showed a considerable increase in current and open circuit voltage when CO2 is added to the O-2 cathode stream, showing high selectivity for carbonate formation.