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 °C and 700 °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 × 10−4 S cm−1 at 700 °C. Semiconducting behaviour was also observed in 5% H2/Ar, albeit with a much smaller activation energy of 0.04(4) eV. Between 300 °C and 700 °C the conductivity ranged from 2.45 S cm−1 to 2.68 S 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.

Graphical abstractDuring our search for anode materials for application in intermediate temperature solid oxide fuel cells, we investigated the conductivity and redox stability of cobalt pyrovanadate.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ Co2V2O7 is an intrinsic semiconductor with a band gap of 1.16(3) eV. ▶ The conductivity of the sample in 5% H2/Ar also exhibits semiconductor behaviour. ▶ In 5% H2/Ar, the conductivity ranged from 2.45 S cm−1 to 2.68 S cm−1. ▶ Co2V2O7 degrade into Co2−xV1+xO4, CoO and VO on reduction. ▶ Co2V2O7 is not a suitable material for redox stable anode for solid oxide fuel cells.