CATALYTIC AND SENSOR PROPERTIES OF Co3O4 PREPARED BY COMBUSTION SYNTHESIS ROUTE

Abstract

Cobalt oxide, Co3O4, has shown great potentials for various practical applications due to excellent electronic, magnetic and redox properties. Its high catalytic activity in combustion of CO is well known for a longer period. However, this material has also drawn some research interest as a p-type metal oxide gas sensor. A powerful strategy to improve both catalytic and sensor performance is the utilization of a nanocrystalline powder with a high surface to volume ratio. Thus, a strong interaction between the surrounding gas and the material is enabled. The nanocrystalline Co3O4 powder was synthesised by the nitrate-glycine combustion route. The glycine/metal ion ratio was adjusted to provide stoichiometric or fuel-lean conditions of the redox reaction. The auto-ignition of gels with the evolution of large amounts of gases was occurred at approximately 180 °C, and the process was spontaneously underwent to a smouldering combustion and formation of a voluminous powder. According to the X-ray diffraction analysis the phase-pure Co3O4 was obtained only when the precursor powder was prepared from the 50% fuel-lean redox reaction. The field emission scanning electron micrographs revealed the spongy aspect of the calcined powder, where small primary particles formed the agglomerates. For the screen-printing, the Co3O4 powder was mixed with the organic binder to achieve a viscous paste suitable for printing. The paste was screen printed onto Al2O3 substrates with interdigitated Pt electrodes for read-out of the resistance and a Pt heater for operation at well controlled temperatures, and fired at 400 °C in air. The catalytic conversion of the Co3O4 powder and the sensor signal of the corresponding sensors were checked under different concentrations of the reducing test gases. The excellent catalytic activity of the Co3O4 powder was confirmed. The sensor signal was the best to ethanol at the operating temperature of 150 °C, which was found to be 100 °C lower than for comercial SnO2 sensors.