Conductivity and stability of cobalt pyrovanadate

Cobalt pyrovanadate was successfully synthesised by a solid state route and the conductivity in both oxidising and reducing environments was determined for the first time. Impedance measurements between 300 degrees C and 700 degrees C in air determined that Co2V2O7 is an intrinsic semiconductor with activation energy of 1.16(3) eV. The conductivity in air reached a maximum of 4 x 10(-4) S cm(-1) at 700 degrees C. Semiconducting behaviour was also observed in 5% H-2/Ar, albeit with a much smaller activation energy of 0.04(4) eV. Between 300 degrees C and 700 degrees C the conductivity ranged from 2.45 S cm(-1) to 2.685 cm(-1), which is approaching the magnitude required for SOFC anode materials. Thermogravimetric analysis found a significant weight loss upon reduction of the compound. X-ray diffraction analysis, coupled with data from previous research, suggested compound degradation into Co2-xV1+xO4, CoO and VO. The redox instability and the low conductivity lead us to the conclusion that cobalt pyrovanadate is unsuitable for utilisation as an anode material for SOFCs although the conductivity is reasonable in a reducing atmosphere. (C) 2010 Elsevier B.V. All rights reserved.