Facile in-situ grown spinel MnCo2O4/MWCNT and MnCo2O4/Ti3C2 MXene composites for high-performance asymmetric supercapacitor with theoretical insight

The logical construction of electrode materials along with greater electrochemical features and solid architectural design is a strategic approach for boosting the electrochemical performance of supercapacitors. However, it is tough and complicated to develop diverse composite materials with better electronic conductivity and greater specific capacitance via rapid and cost-effective synthesis procedures. Herein, we propose a straightforward and simple approach by employing the hydrothermal technique for the synthesis of spinel MnCo2O4 composite nanostructures using 1D MWCNT and 2D MXene (Ti3C2Tx) materials with detailed analysis of the supercapacitor performance as compared to existing literature on similar studies. The MCO/TCX (MnCo2O4/Ti3C2Tx) composite shows an impressive capacitance of 860.22 F/g at a current density of 2 A/g after electrochemical optimization. Furthermore, an asymmetric supercapacitor device (ASCs) was constructed using MCO and its composites MCO/MWCNT and MCO/TCX as a positive, and AC was employed as a negative electrode to test its device capability. Comparatively, the MCO/TCX//AC SC device demonstrated exceptional energy storage properties with a better specific capacitance value of 126.58 F/g at 0.8 A/g of current density, an elevated energy density of 40 Wh/kg, with a power density of 4828 W/kg along a capacitance retention rate of 87 % over 5000 cycles, suggesting better cycle life. Whereas, the MCO/MWCNT//AC device shows a better cycling performance of 91 % after 5000 cycles with a superior energy and power density of 27.04 Wh/kg and 1448 W/kg respectively. Also the theoretical insight for further understanding of the charge-storage mechanism through DFT calculations provides an estimate of electronic properties and quantum capacitance calculated for the pristine MCO and its hybrids with CNT and Ti3C2Tx MXene and information on the interactions between orbitals, the bonding process, and the charge transfer capabilities of each electrode material. The theoretical studies also confirm that the electronic properties and therein charge storage performance have an increasing trend in the order of MCO < MCO/CNT < MCO/TCX consistent with the experimental findings. Additionally, these simulations conclude that the hybrid MCO/TCX has the largest quantum capacitance which is in accordance with the findings of the experiments. The improved performance of MCO/TCX is due to the enlarged surface area that allows higher charge transfer from TCX to MCO. The charge transferred from the C 2p orbital of TCX to the Mn 3d orbital of MCO is the leading cause for the capacitance improvement mechanism of hybrid MCO/TCX. This work offers a simple procedure for developing energy storage devices using spinel MnCo2O4-based composite electrode materials supported by 1D carbon nanotube and 2D MXene that offer superior electrochemical performance and the fabricated electrodes that could be employed further for energy storage-based applications.