Recently, we have compared the supercapacitance of MnFe 2O 4, CoFe 2O 4, and NiFe 2O 4 nanoparticles, and found that MnFe 2O 4 exhibits better supercapacitance properties 14, 15. It has also been demonstrated that the spinel ferrites of these metals (MFe 2O 4, M is a transition metal) deliver much better electrochemical performance due to their richer valence electron, different redox states, synergistic effects between their metal ions, electrochemical stability, and chemical and mechanical stability, suitable for batteries and supercapacitors 14, 25, 26, 27, 28, 29. In particular, few-layer MoS 2 nanosheets have been found promising because of their large surface area, which acts as a substrate to hold other nanoparticles, and high thermal stability 16.Īmong various transition metals 17, nickel, manganese, and cobalt are promising in the field of supercapacitors due to their high electrochemical activity and low cost as well as the abundance of their oxide/hydroxide compounds 18, 19, 20, 21, 22, 23, 24. In general, TMDs make use of fast and reversible faradaic redox reactions (also known as pseudocapacitance) that involve ions and electrons in their charge storage mechanism 14, 15. Recent developments suggest that 2D transition metal dichalcogenides (TMDs) such as MoS 2, MoSe 2, WS 2, TiS 2, NbS 2, and VS 2 have great potential to fill the gap between the current performance and the modern requirements of energy-storage devices as electrodes of electrochemical supercapacitors 10, 11, 12, 13. There has been recently growing attention to two-dimensional (2D) layered materials for a variety of applications including energy production and storage, sensors, photocatalysts, etc. However, it is yet challenging to design and develop electrode materials to realize these anticipated features and efficiently store/deliver energy 4, 5, 6. There are two classifications for supercapacitors based on their energy storage mechanisms: (1) electrochemical double-layer capacitors that accumulate charges at their electrode/electrolyte interface and (2) pseudocapacitors that handle charges via fast and reversible redox reactions on electrochemically active sites 3. Supercapacitors are among the most-promising energy-storage devices owing to their longer lifespan than secondary batteries and their higher capacitance and reliability than conventional dielectric capacitors 2. Therefore, it is indispensable to develop energy-storage devices with high energy capacities, long lifetimes, and high cycling stability to overcome the impending exhaustion of fossil fuel reserves and alleviate environmental concerns 2. There have been increasing demands in the past few decades for superior energy storage and conversion devices to address the basic energy-related needs of the ever-growing population in the world 1. A density functional theory study was also performed on the MnFe 2O 4/MoS 2 interface to analyze how a MoS 2 monolayer can enhance the electronic properties of MnFe 2O 4 towards a higher specific capacitance. We also demonstrated a real-world application of the MnFe 2O 4/MoS 2 nanocomposite in a two-cell asymmetric supercapacitor setup. Electrochemical tests showed that the incorporation of MoS 2 nanosheets largely increased the specific capacitance of MnFe 2O 4 from 600 to 2093 F/g (with the corresponding energy density and power density of 46.51 Wh/kg and 213.64 W/kg, respectively) at 1 A/g, and led to better charge–discharge cycling stability.
UV–visible absorption photospectrometry indicated a decrease in the bandgap of MnFe 2O 4 by MoS 2, resulting in a higher conductivity that is suitable for capacitance. Transmission electron microscopy images showed the uniform size distribution of MnFe 2O 4 nanoparticles (~ 13 nm) on few-layer MoS 2 nanosheets. X-ray diffractometry and Raman spectroscopy confirmed the crystalline structures and structural characteristics of the nanocomposite. Manganese ferrite (MnFe 2O 4) nanoparticles were synthesized via a hydrothermal method and combined with exfoliated MoS 2 nanosheets, and the nanocomposite was studied as a supercapacitor.
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