Facile synthesis route of porous MnCo2O4 and CoMn2O4 nanowires and their excellent electrochemical properties in supercapacitors

Abstract

Two types of porous cobalt manganese oxide nanowires (MnCo₂O₄ and CoMn₂O₄) with different structures have been successfully synthesized by thermal decomposition of organometallic compounds for the first time. Nitrilotriacetic acid (NA) was used as a chelating agent to coordinate Co(II) and Mn(II) ions in various molar ratios, in a hydrothermal condition. The microstructure of as-synthesized cobalt manganese oxides, composed of numerous nanoparticles, completely retains the 1D network structure of the Co–Mn–NA coordination precursors without structure collapse. Electrochemical properties of the cobalt manganese oxide materials have been tested for supercapacitors at room temperature. Both the MnCo₂O₄ and CoMn₂O₄ electrodes display the outstanding capacitive behaviors and superior electrochemical properties. The CoMn₂O₄ nanowire shows excellent capacitance and desirable rate performance (2108 F g⁻¹ at 1 A g⁻¹ and 1191 F g⁻¹ at 20 A g⁻¹) compared to that of the MnCo₂O₄ nanowire (1342 F g⁻¹ at 1 A g⁻¹ and 988 F g⁻¹ at 20 A g⁻¹). Electrochemical impedance spectra (EIS) results also reconfirm that the CoMn₂O₄ nanowires display more facile electrolyte diffusion and higher capacitor response frequency than MnCo₂O₄ nanowires. This can be ascribed to the facile electrolyte/OH⁻ ion penetration and better Faradaic utilization of the electroactive surface sites that generated by the smaller particle size and higher surface area.