Supercapacitors are an alternative to batteries. They charge and discharge very fast, but usually have much smaller capacities. Co₃O₄ nanosheets are a material with a high theoretical specific capacitance, which could improve the energy storage capacity of supercapacitors.

Xuefeng Guo, Nanjing University and Huanggang Normal University, both China, and colleagues have synthesized a range of two-dimensional Co₃O₄ nanosheets with different amounts of oxygen vacancies for use in supercapacitors. The team first prepared cobalt hydroxide precursors, which were calcined at 300 °C in air to give Co₃O₄ nanosheets. The nanosheets were then reduced to create oxygen vacancies, either in a mixture of hydrogen and nitrogen or in an NaBH₄ solution. The resulting nanosheets have a thickness of about 20 nm and retain the overall structure of pristine Co₃O₄ nanosheets.

The researchers found an increasing number of oxygen vacancies from the pristine nanosheets, to the hydrogen-reduced ones, to the NaBH₄-reduced material. The electrical conductivities and specific capacitances of the respective nanosheets increase in the same order. The oxygen-vacancy-rich NaBH₄-reduced Co₃O₄ nanosheets have an excellent electrochemical performance, making them a promising material for supercapacitors.

• Two dimensional oxygen-vacancy-rich Co₃O₄ nanosheets with excellent supercapacitor performances,
  Kun Xiang, Zhicheng Xu, Tingting Qu, Zhengfang Tian, Yu Zhang, Yongzheng Wang, Mingjiang Xie, Xiangke Guo, Weiping Ding, Xuefeng Guo,
  Chem. Commun. 2017.
  DOI: 10.1039/c7cc07515d