Effects of solvent on the morphology of nanostructured Co₃O₄ and its application for high-performance supercapacitors

Graphical abstract: - Highlights: • Nano-structured cobalt oxides (Co₃O₄) with various morphologies (sheet-like, herbs-like and net-like) synthesized on the surfaces of nickel foam via a facile solvothermal method. • Ethanol, ethylene glycol (EG) and glycerol (GR) were used to investigate the effects of solvent on the size and morphology of nanocrystals in detail. • The open structure improves the contact between the electrode and the electrolyte. • Results showed that net-like Co₃O₄ have good electrochemical property. - Abstract: Nano-structured cobalt oxides (Co₃O₄) with various morphologies (sheet-like, herbs-like and net-like) have been in situ synthesized on the surface of nickel foam via a facile solvothermal method. Ethanol, ethylene glycol (EG) and glycerol (GR) were used to investigate the effects of solvent on the size and morphology of nanocrystals in detail. The possible formation mechanisms have been proposed that the dielectric constants and viscosity of solvents is speculated to be the main factor to determine the morphology of Co₃O₄ crystal. Applied for supercapacitor, the fabricated Co₃O₄ electrodes show the desired properties of macroporosity, allowing facile electrolyte flow and fast electrochemical reaction kinetics. Results show that the nanonet-like Co₃O₄ electrode synthesized in glycerol solvothermal condition has the highest capacitance (1063 F/g at a discharge current density of 10 mA/cm²), and good rate capability, excellent electrochemical stability (90.8% retention after 1000 cycles). The enhanced electrochemical performance is attributed to the open and ultrathin nanostructure of net-like Co₃O₄ electrode, which facilitates the electron transport. The findings in this work demonstrate the importance of solvents used for solvothermal reaction, and are meaningful in understanding the self-assembly process of various Co₃O₄ nanostructures