MoS₂-Modified Zinc Magnetite Nanocomposites for High-Performance Asymmetric Supercapacitors

The demand for sustainable energy storage drives the development of eco-friendly, energy-efficient methods for high-performance electrode materials. Conventional synthesis of transition metal oxides often involves high-temperature calcination, resulting in high energy consumption and carbon emissions. Here, we present a calcination-free, low-temperature co-precipitation method to synthesize ZnMn₂O₄ (ZMO) and its nanocomposite with two-dimensional MoS₂ (MS), denoted as ZnMn₂O₄/x%MoS₂ (x-ZMS). Incorporating MS significantly enhances the ZMO-specific capacitance, ion diffusion, and structural stability. The optimized ZnMn₂O₄/20%MoS₂ (20-ZMS) composite delivers a specific capacitance of 575 F g^-1 at 0.5 Ag^1-, with 95% retention over 10,000 cycles at 7 Ag^1- and a Coulombic efficiency of ∼100%. These improvements arise from the synergy between the ZMO redox activity and MS layered structure, high conductivity, and large electroactive surface area. The composite also exhibits a high surface area (99.76 m² g^-1) and hierarchical porosity, enabling efficient charge transport. An asymmetric supercapacitor (ASC) using 20-ZMS as a positive electrode, activated carbon (AC) as a negative electrode, and PVA-KOH gel as both an electrolyte and a separator delivers an energy density of 48 Wh kg^-1 and a power density of 16 kW kg^-1, retaining 98% capacitance after 20,000 cycles. Two such devices light three green LEDs for 4 min, demonstrating strong practical potential.