One-step large scale combustion synthesis mesoporous MnO2/MnCo2O4 composite as electrode material for high-performance supercapacitors

In-situ construction of binder-free MnO2/MnSe heterostructure membrane for high-performance energy storage in pseudocapacitors

Manganese (Mn)-based oxides are considered suitable positive electrode materials for supercapacitors (SCs). However, their cycle stability and specific capacitance are significantly hindered by key restrictions such as structural instability and low conductivity. Herein, we demonstrated a novel nanorod (NR)-shaped heterostructured manganese dioxide/manganese selenide membrane (MnO2/MnSe) on carbon cloth (CC) (denoted as MnO2/MnSe-NR@CC) with a high aspect ratio by a straightforward and facile hydrothermal process. Experiments have demonstrated that doping selenium atoms to oxygen sites reduce electronegativity, increasing the intrinsic electronic conductivity of MnO2, decreasing electrostatic interactions with electrolyte ions, and thus boosting the reaction kinetics. Further, the selenium doping results in an amorphous surface with extensive oxygen defects, which contributed to the emergence of additional charge storage sites with pseudocapacitive characteristics. As expected, novel heterostructured MnO2/MnSe-NR@CC as an electrode for SC exhibits a high capacitance of 740.63 F/g at a current density of 1.5 A/g, with excellent cycling performance (93% capacitance retention after 5000 cycles). The MnO2/MnSe-NR@CC exhibited outstanding charge storage capability, dominating capacitive charge storage (84.6% capacitive at 6 mV/s). To examine the practical applications of MnO2/MnSe-NR@CC-ASC as a positive electrode, MnO2/MnSe-NR@CC//AC device was fabricated. The MnO2/MnSe-NR@CC//AC-ASC device performed exceptionally well, with a maximum capacitance of 166.66 F/g at 2 A/g, with a capacitance retention of 94%, after 500 GCD cycles. Additionally, it delivers an energy density of 75.06 Wh/kg at a power density of 1805.1 W/kg and maintains 55.044 Wh/kg at a maximum power density of 18,159 W/kg. This research sheds fresh information on the anionic doping method and has the potential to be applied to the synthesis of positive electrode materials for energy storage applications.

Facile Hydrothermal Synthesis of Binder-Free Hexagonal MnO2 Nanoparticles for a High-Performance Supercapacitor’s Electrode Material

Manganese dioxide (MnO2)-based nanostructures are promising electrode materials for supercapacitors (SCs) due to their low cost, eco-friendly nature, and high theoretical capacitance. However, the conductivity of MnO2 is poor, which is a big problem when trying to achieve the desired capacitance value. Herein, hexagonal-phase MnO2 nanoparticles (NPs) are directly grown on a 3D conductive carbon cloth (CC) (denoted as MnO2-NPs@CC) as a binder-free electrode through a simple and scalable hydrothermal strategy. The results show that MnO2-NPs@CC with a large specific surface area and high porosity could be employed as a positive electrode material for high-performance SCs. Owing to these attractive properties, the MnO2-NPs@CC electrode delivers a high specific capacitance of 660 F/g at a current density of 2 A/g in 6 M KOH aqueous electrolytes. Moreover, the MnO2-NPs@CC electrode demonstrates excellent cycling stability with high capacitance retention of 92.8% over 10,000 cycles. Such remarkable findings suggest that MnO2-NPs@CC with enhanced electrochemical performance is a favorable electrode material for next-generation high-performance SCs.

Effective regeneration of mixed composition of spent lithium-ion batteries electrodes towards building supercapacitor

Recycling of different manufacturers of spent lithium-ion batteries cathode and anode via a simple regeneration process has an opportunity to fabricate new energy devices. In this study, the different manufacturers of spent LIB cathode pieces were subjected to lixiviation process and found the best-optimized conditions such as tartaric acid concentration (2.5 M), H₂O₂ concentration (7.5 vol%), solid-liquid ratio (80 g/L), temperature (80 °C), and lixiviation time (80 min) for maximum ~ 99% extraction efficiency of metals. Further, 3D-MnCo₂O₄ (MCO) spheres were regenerated from the cathode lixivium containing metal ions via hydrothermal technique. Besides, anode graphite and Al foils after cathode lixiviation were exploited to prepare reduced graphene oxide (RGO) at room temperature in a simple method. The electrochemical performance of both regenerated electrodes from spent LIBs was explored in the half-cell configuration using the 1 M Na₂SO₄ electrolyte. Additionally, the constructed MCO//RGO asymmetric supercapacitor device offers an operational voltage of 1.8 V and displays a high energy density of ~ 23.9 Wh kg^-1 at 450 W kg^-1 with 8000 cycles. This alternative recycling method proposes the possibility to construct high-energy storage devices from different compositions of spent LIBs.

Porous carboxymethyl cellulose carbon of lignocellulosic based materials incorporated manganese oxide for supercapacitor application

The present work developed porous carboxymethyl cellulose (CMC) carbon film from lignocellulosic based materials as supercapacitor electrode. Porous CMC carbon films of bamboo (B) and oil palm empty fruit bunch (O) were prepared through simple incipient wetness impregnation method followed by calcination process before incorporation with manganese oxide (Mn₂O₃). The carbonization produced porous CMC carbon whereby CMCB exhibited higher surface area than CMCO. After Mn₂O₃ incorporation, the crystallite size of CMCB and CMCO were calculated as 50.09 nm and 42.76 nm, respectively whereas Mn₂O₃/CMCB and Mn₂O₃/CMCO composite films were revealed to be 26.71 nm and 35.60 nm in size, respectively. Comparatively, the Mn₂O₃/CMCB composite film exhibited higher electrochemical performance which was 31.98 mF cm^-2 as compared to 24.15 mF cm^-2 by Mn₂O₃/CMCO composite film and both CMC carbon films with fairly stable cycling stability after 1000 charge-discharge cycles. Therefore, it can be highlighted that Mn₂O₃/CMC composite film as prepared from bamboo and oil palm fruit can potentially become the new electrode materials for supercapacitor application.

The Influence of the Electrodeposition Parameters on the Properties of Mn-Co-Based Nanofilms as Anode Materials for Alkaline Electrolysers

In this work, the influence of the synthesis conditions on the structure, morphology, and electrocatalytic performance for the oxygen evolution reaction (OER) of Mn-Co-based films is studied. For this purpose, Mn-Co nanofilm is electrochemically synthesised in a one-step process on nickel foam in the presence of metal nitrates without any additives. The possible mechanism of the synthesis is proposed. The morphology and structure of the catalysts are studied by various techniques including scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The analyses show that the as-deposited catalysts consist mainly of oxides/hydroxides and/or (oxy)hydroxides based on Mn²⁺, Co²⁺, and Co³⁺. The alkaline post-treatment of the film results in the formation of Mn-Co (oxy)hydroxides and crystalline Co(OH)₂ with a β-phase hexagonal platelet-like shape structure, indicating a layered double hydroxide structure, desirable for the OER. Electrochemical studies show that the catalytic performance of Mn-Co was dependent on the concentration of Mn versus Co in the synthesis solution and on the deposition charge. The optimised Mn-Co/Ni foam is characterised by a specific surface area of 10.5 m²·g⁻¹, a pore volume of 0.0042 cm³·g⁻¹, and high electrochemical stability with an overpotential deviation around 330–340 mV at 10 mA·cm⁻²_geo for 70 h.

Facile Synthesis of Yolk-Shelled CuCo2Se4 Microspheres as a Novel Electrode Material for Supercapacitor Application

Recently, metal selenides have attracted much attention in the energy storage applications. This attention is due to the outstanding properties of metal selenides (lower cost, lower electronegativity, and environmental friendliness) compared to metal sulfides and oxides. In this work, novel yolk-shelled CuCo₂Se₄ (YS-CCS) microspheres are synthesized by a facile two-step hydrothermal method and used as an electrode material for high-performance supercapacitors (SCs) in alkaline media. The proposed YS-CCS electrode shows remarkable electrochemical performance, including fast kinetics, high reversibility, low internal resistance (0.45 Ω), excellent specific capacitance (512 F g^-1 at a current density of 1A g^-1), high rate capability (70.8% after increasing the current density six times), and good cycling stability (about 83.7% of the initial retention after 6000 successive charge-discharge cycles). Furthermore, an asymmetric supercapacitor (ASC) is assembled by using the YS-CCS (as a cathode electrode material) and active carbon (as an anode electrode material). The assembled device delivers a maximum energy density of 9.45 W h kg^-1 and a power density up to 850 W kg^-1 in a wide potential window of 1.70 V. Meanwhile, the ASC device exhibits superb rate capability (∼84.67%) after increasing the current density five times and very good capacitance retention (∼88%) after 6000 cycles.

Synthesis of MnCo2O4 nanoparticles as modifiers for simultaneous determination of Pb(II) and Cd(II)

The porous spinel oxide nanoparticles, MnCo₂O₄, were synthesized by citrate gel combustion technique. Morphology, crystallinity and Co/Mn content of modified electrode was characterized and determined by Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction pattern analysis (XRD), simultaneous thermogravimetry and differential thermal analysis (TG/DTA). Nanoparticles were used for modification of glassy carbon electrode (GCE) and new sensor was applied for simultaneous determination of Pb(II) and Cd(II) ions in water samples with the linear sweep anodic stripping voltammetry (LSASV).The factors such as pH, deposition potential and deposition time are optimized. Under optimal conditions the wide linear concentration range from 0.05 to 40 μmol/dm³was obtained for Pb(II), with limit of detection (LOD) of 8.06 nmol/dm³ and two linear concentration ranges were obtained for Cd(II), from 0.05 to 1.6 μmol/dm³ and from 1.6 to 40 μmol/dm³, with calculated LOD of 7.02 nmol/dm³. The selectivity of the new sensor was investigated in the presence of interfering ions. The sensor is stable and it gave reproducible results. The new sensor was succesfully applied on determination of heavy metals in natural waters.

A MnCo2 O4 @NiMoO4 Core-Shell Composite Supported on Nickel Foam as a Supercapacitor Electrode for Energy Storage

A MnCo₂ O₄ @NiMoO₄ composite was synthesized on nickel foam by a two-step method. The composite has a core-shell structure in which MnCo₂ O₄ nanoneedles are wrapped by NiMoO₄ nanoflakes. The MnCo₂ O₄ @NiMoO₄ /Ni foam is applied as a binder-free electrode for supercapacitors and it achieves a specific capacitance of up to 1718 F g^-1 at a current density of 1 A g^-1 , and 84 % capacitance retention after 6000 charge-discharge cycles. The capacitance of the MnCo₂ O₄ @NiMoO₄ composite is much higher than MnCo₂ O₄ nanoneedles and NiMoO₄ nanoflakes alone. Moreover, a hybrid supercapacitor is assembled by applying the MnCo₂ O₄ @NiMoO₄ /Ni foam as the positive electrode, activated carbon/Ni foam as the negative electrode. The hybrid supercapacitor reaches an energy density of up to 42.3 W h kg^-1 at a power density of 797 W kg^-1 , a power density of 6256 W kg^-1 at an energy density of 17.4 W h kg^-1 , and 86 % capacitance retention after 2000 charge-discharge cycles. The results suggest that the rational design of electrode materials with such structure and composition is an effective strategy to improve electrochemical performance.

Rational design of MnCo2O4@NC@MnO2 three-layered core–shell octahedron for high-rate and long-life lithium storage

With the depletion of fossil energy and rapid development of electronic equipment, the commercial lithium-ion batteries (LIBs) do not meet the current energy demand.

Morphology-Conserved Transformations of Metal-Based Precursors to Hierarchically Porous Micro-/Nanostructures for Electrochemical Energy Conversion and Storage

To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.

The synergistic effect achieved by combining different nitrogen-doped carbon shells for high performance capacitance

The superior capacitance performance was achieved by a mixture of two types of ellipsoid nitrogen-doped hollow carbon shells.

High-Performance Asymmetric Supercapacitors of MnCo2O4 Nanofibers and N-Doped Reduced Graphene Oxide Aerogel

The working potential of symmetric supercapacitors is not so wide because one type of material used for the supercapacitor electrodes prefers either positive or negative charge to both charges. To address this problem, a novel asymmetrical supercapacitor (ASC) of battery-type MnCo₂O₄ nanofibers (NFs)//N-doped reduced graphene oxide aerogel (N-rGO_AE) was fabricated in this work. The MnCo₂O₄ NFs at the positive electrode store the negative charges, i.e., solvated OH^-, while the N-rGO_AE at the negative electrode stores the positive charges, i.e., solvated K⁺. An as-fabricated aqueous-based MnCo₂O₄//N-rGO_AE ASC device can provide a wide operating potential of 1.8 V and high energy density and power density at 54 W h kg^-1 and 9851 W kg^-1, respectively, with 85.2% capacity retention over 3000 cycles. To understand the charge storage reaction mechanism of the MnCo₂O₄, the synchrotron-based X-ray absorption spectroscopy (XAS) technique was also used to determine the oxidation states of Co and Mn at the MnCo₂O₄ electrode after being electrochemically tested. The oxidation number of Co is oxidized from +2.76 to +2.85 after charging and reduced back to +2.75 after discharging. On the other hand, the oxidation state of Mn is reduced from +3.62 to +3.44 after charging and oxidized to +3.58 after discharging. Understanding in the oxidation states of Co and Mn at the MnCo₂O₄ electrode here leads to the awareness of the uncertain charge storage mechanism of the spinel-type oxide materials. High-performance ASC here in this work may be practically used in high-power applications.

MnO2 nanotubes with a water soluble binder as high performance sodium storage materials

Well dispersed MnO₂ nanotubes were synthesized via a hydrothermal method.

Flexible heterostructured supercapacitor electrodes based on α-Fe2O3 nanosheets with excellent electrochemical performances

Hybrid α-Fe₂O₃@Co₃O₄ and α-Fe₂O₃@MnCo₂O₄ composites are successfully synthesized on flexible carbon cloth, respectively. These as-obtained products as the supercapacitor electrodes show enhanced discharge areal capacitance.