Effect of various aqueous electrolytes on the electrochemical performance of α-MnO2 nanorods as electrode materials for supercapacitor application

Significant Electrode of Supercapattery Devices: the Induced Charge Storage Capability of MoSe2/rGO Nanosheets Bedecked by MnO2 Nanorod Composites

This work emphasizes the procedure with three stages, including a forthright hydrothermal technique for synthesizing a composite material of layered MoSe2/rGO and MnO2 nanorods. The developed electrodes explicitly show the supercapacitor and battery storage capability (i.e., supercapattery), unveiling a higher operating potential value and energy density. This is mainly attributed to the structure and high surface-to-volume ratio of 2D MoSe2/rGO nanosheets, which provide rapid charge storage aptitudes, enormous active sites, decreased electronic/ionic resistance, and rich electron transfer characteristics. The MnO2/MoSe2/rGO composite has an optimum surface area (78.24 m2 g-1) and an immense microspore structure (12.9 nm), which is due to the layered construction of MoSe2 with rGO nanosheets. The MnO2/MoSe2/rGO composite has robust electrochemical characteristics, achieving 950 F g-1 of specific capacitance at 1 A g-1 of current density and demonstrating cyclic stability of 90% after 10,000 continuous cycles. In addition, an asymmetric supercapattery device of AC//MnO2/MoSe2/rGO showcased the specific capacitance and capacity of 85.1 F g-1 and 153.18 C g-1 at 1 A g-1, as well as achieved an energy and power density of 30.2 W h/kg and 807 W/kg in 1.8 V. Also, a real-time practical device is tested using two distinct varieties of light-emitting diodes and offered with an effective discharge time of 14 min. The enriched electrochemical performances of MnO2/MoSe2/rGO composites and the extensive features of supercapattery electrodes may have potential for the expanded charge storage realm in modern energy storage materials.

Research Progress on Microwave Synthesis of 3d Transition Metal (Mn, Fe, Co, and Ni) Oxide Nanomaterials for Supercapacitors

3d transition metal oxides composed of Mn, Fe, Co, and Ni have emerged as promising candidates for supercapacitor electrode materials due to their high theoretical specific capacitance, abundant redox-active sites, variable oxidation states, environmental friendliness, and low cost. Various synthesis strategies have been developed to fabricate these nanostructures, including hydrothermal/solvothermal methods, sol-gel processing, and microwave-assisted synthesis. Among them, microwave irradiation technology, with its rapid heating characteristics and unique thermal/non-thermal effects, offers significant advantages in controlling crystallinity and particle size distribution, suppressing particle agglomeration, and enhancing material purity. Furthermore, microwave effects facilitate the self-assembly and morphological evolution of transition metal oxides, promote the formation of crystal defects, and strengthen interfacial interactions. These effects enable precise microstructural tuning, leading to an increased specific surface area and a higher density of active sites, ultimately enhancing specific capacitance, rate capability, and cycling stability. In recent years, microwave-assisted synthesis has made significant progress in constructing 3d transition metal oxides and their composites, particularly in the development of single-metal and binary-metal oxides, as well as their hybrids with carbon-based materials (e.g., graphene and carbon nanotubes) and other metal oxides. This review systematically summarizes the research progress on microwave-assisted techniques for 3d transition metal oxide-based nanomaterials, with a particular focus on the role of microwave effects in morphology control, interfacial optimization, and electrochemical performance enhancement. Additionally, key challenges in current research are critically analyzed, and potential optimization strategies are proposed. This review aims to provide new insights and perspectives for advancing microwave-assisted synthesis of 3d transition metal oxides in energy storage applications.

Improved MnO2 based electrode performance arising from step by step heat treatment during electrodeposition of MnO2 for determination of paracetamol, 4-aminophenol, and 4-nitrophenol

The design of electrochemical sensors is crucial considering important factors such as efficiency, low cost, biocompatibility, and availability. Manganese oxides are readily available, low-cost, and biocompatible materials, but their low conductivity limits their efficiency as sensors. Today, morphology engineering of manganese oxide has been one of the most common research topics, because manganese oxides' electrochemical properties are highly dependent on their morphologies. In this study, a method for reducing the charge transfer resistance (Rct) of MnO2-based electrodes was established by the cyclic voltammetry technique accompanied by step-by-step heat treatment to electrodeposition MnO2 nanofilm, which remarkably improved the Rct. Next, the sensing performance of MnO2/FTO for two separate measurements was examined, one for the simultaneous measurement of paracetamol (PAR) and 4-aminophenol (4-APh), and the other for the measurement of 4-nitrophenol (4-NP). Under the optimum conditions, the linear ranges of 4-APh, PAR, and 4-NP, were 0.8 to 22.0 µM, 2.0 to 55.0 µM, and 0.1-250 µM, with limits of detection (LOD) of 0.19 µM, 0.60 µM, and 0.01 µM, respectively. It also was unaffected by a 200-fold excess of interferences. In addition, the designed sensor was successfully applied to the analysis of real samples.

Unravelling the effect of crystal lattice compression on the supercapacitive performance of hydrothermally grown nanostructured hollandite α-MnO2 induced by incremental growth time

Manganese oxide (α-MnO2) nanoparticles are highly recognised for their use in supercapacitor applications. This study demonstrates the successful synthesis of flower-like and nanorods hollandite α-MnO2 by a simple one-pot hydrothermal technique at various reaction times. The synthesised nanoparticles were characterised by various physicochemical and electrochemical characterisation techniques. The influence of the various reaction times on the structural and morphological properties was evaluated by X-ray diffraction (XRD) and scanning electron microscope. XRD patterns revealed that the synthesized MnO2 nanoparticles are tetragonal structures with crystallite sizes ranging from 13.69 to 20.37 nm estimated from the Williamson-Hall method. Moreover, the functional groups and surface area were examined by Fourier transform infrared spectroscopy and Bruner-Emmert-Teller, respectively. Furthermore, the compositional elements were studied by X-ray photoemission spectroscopy and energy-dispersive X-ray spectroscopy. Finally, the electrochemical performances were studied using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS). The GCD characteristics revealed that the optimised α-MnO2 has a good capacitive behaviour, which predicts the potential application in energy storage. Electrochemical studies revealed that the 3 h-MnO2 sample exhibited a superior electrochemical behaviour and demonstrated a high specific capacitance of 132 F/g at a current density of 1A/g.

Facile Preparation of Carbon Nanotubes/Cellulose Nanofibrils/Manganese Dioxide Nanowires Electrode for Improved Solid-Sate Supercapacitor Performances

Wearable energy storage devices require high mechanical stability and high-capacitance flexible electrodes. In this study, we design a flexible supercapacitor electrode consisting of 1-dimensional carbon nanotubes (CNT), cellulose nanofibrils (CNF), and manganese dioxide nanowires (MnO2 NWs). The flexible and conductive CNT/CNF-MnO2 NWs suspension was first prepared via ultrasonic dispersion approach, followed by vacuum filtration and hot press to form the composite paper electrode. The morphological studies show entanglement between CNT and CNF, which supports the mechanical properties of the composite. The CNT/CNF-MnO2 NWs electrode exhibits lower resistance when subjected to various bending angles (-120-+120°) compared to the CNT/CNF electrode. In addition, the solid-state supercapacitor also shows a high energy density of 38 μWh cm-2 and capacitance retention of 83.2% after 5000 cycles.

Incorporation of α-MnO2 Nanoflowers into Zinc-Terephthalate Metal-Organic Frameworks for High-Performance Asymmetric Supercapacitors

Herein, we report the synthesis of α-MnO₂ nanoflower-incorporated zinc-terephthalate MOFs (MnO₂@Zn-MOFs) via the conventional solution phase synthesis technique as an electrode material for supercapacitor applications. The material was characterized by powder-X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The prepared electrode material exhibited a specific capacitance of 880.58 F g^-1 at 5 A g^-1, which is higher than the pure Zn-BDC (610.83 F g^-1) and pure α-MnO₂ (541.69 F g^-1). Also, it showed a 94% capacitance retention of its initial value after 10,000 cycles at 10 A g^-1. The improved performance is attributed to the increased number of reactive sites and improved redox activity due to MnO₂ inclusion. Moreover, an asymmetric supercapacitor assembled using MnO₂@Zn-MOF as the anode and carbon black as the cathode delivered a specific capacitance of 160 F g^-1 at 3 A g^-1 with a high energy density of 40.68 W h kg^-1 at a power density of 20.24 kW kg^-1 with an operating potential of 0-1.35 V. The ASC also exhibited a good cycle stability of 90% of its initial capacitance.

N-Doped carbon as the anode and ZnCo2O4/N-doped carbon nanocomposite as the cathode for high-performance asymmetric supercapacitor application

Herein, we report a one-pot hydrothermal assisted synthesis of ZnCo₂O₄/N-doped carbon nanocomposite (ZC/NC) for high-performance asymmetric supercapacitor applications.