One pot, rapid synthesis of Co₃O₄ by solution combustion method and its electrochemical properties in different electrolytes

Nano-crystalline Co₃O₄ is synthesized using solution combustion method. Characterization is done using XRD, TEM and BET surface area analysis. XRD shows pure nano-crystalline phase of Co₃O₄. Crystallinity of as prepared material improves by calcining the compound at 900 °C for 10 h while no effect is seen at 600 °C. TEM studies show that particles of around 50 nm size are formed at 400 °C. At 600 °C a well-defined hexagonal morphology could be seen both by TEM and SEM and the particle size is around 70 nm. However, TEM of the sample at 900 °C shows big agglomerates of cobalt oxide and no specific geometry could be obtained. Estimated BET surface area for the sample calcined at 600 °C is 10 m²/g. Detailed electrochemical studies are carried out in neutral and basic electrolytes where Ag/AgCl is used as the reference electrode. It is found that Co₃O₄ is active for oxygen evolution reaction in basic medium as well as in neutral medium. KOH is used as the basic medium while KNO₃, K₂SO₄ and phosphate buffer is used for neutral medium. However, it is not active for hydrogen evolution reaction in any of the medium even at − 1.0 V. This is confirmed by gas analysis of the output gas in the cell by using a mass spectrometer. When compared with the buffer medium, it is observed that local pH changes in KNO₃ and K₂SO₄ medium are possibly affecting the oxygen evolution reaction.