Improved electrochemical performance and charge storage mechanism of NiMnCoO4 by XPS study

Abstract

Ni and Mn-based oxides are gaining more attention in supercapacitor applications due to their high abundance and high specific capacitance. However, the charge storage mechanism is not yet clearly understood. In this study, we have synthesized NiMn2O4 and NiMnCoO4 by hydrothermal method followed by annealing at a temperature of 400 °C for 4 h and tried to understand their charge storage mechanism by XPS study. The capacitance property of synthesized materials NiMn2O4 (NMO) and NiMnCoO4 (NMCO) is evaluated for supercapacitor application. The NiMn2O4 exhibits a specific capacitance of 260 F g−1 when cycled at 0.6 A g−1. At the same specific current, NiMnCoO4 exhibits 298.5 F g−1. When both the samples were cycled at 2 A g−1, the capacitance retentions of NMO and NMCO are found to be 80% and 100%, respectively after 5000 cycles. The XPS study clearly indicates the involvement of Mn2+/Mn3+ and Mn3+/Mn4+ redox reaction in the charge storage of NiMn2O4 while that of Co2+/Co3+ redox couple in the charge storage process of NiMnCoO4. This result clearly indicates the higher specific capacitance and better cycling stability of NiMnCoO4 over NiMn2O4. Although, there are a lot of reports on the capacitance property of NMO, there is rare report on NMCO material. So, we have studied their electrochemical properties and charge storage mechanism by using XPS for supercapacitor application.