Direct electro-synthesis of MnO2 nanoparticles over nickel foam from spent alkaline battery cathode and its supercapacitor performance

Preparation of Manganese Oxide Nanoparticles with Enhanced Capacitive Properties Utilizing Gel Formation Method

Development of efficient and environmentally benign materials is important to satisfy the increasing demand for energy storage materials. Nanostructured transition-metal oxides are attractive because of their variety in morphology, high conductivity, and high theoretical capacitance. In this work, the nanostructured MnO₂ was successfully fabricated using a gel formation process followed by calcination at 400 °C (MNO4) and 700 °C (MNO7) in the presence of air. The suitability of the prepared materials for electrochemical capacitor application was investigated using graphite as an electrode substrate. The chemical, elemental, structural, morphological, and thermal characterizations of the materials were performed with relevant techniques. The structural and morphological analyses revealed to be a body-centered tetragonal crystal lattice with a nano-tablet-like porous surface. The capacitive performances of the MNO4- and MNO7-modified graphite electrodes were examined with cyclic voltammetry and chronopotentiometry in a 0.5 M Na₂SO₄ aqueous solution. The synthesized MNO7 demonstrated a higher specific capacitance (627.9 F g^-1), energy density (31.4 Wh kg^-1), and power density (803.5 W kg^-1) value as compared to that of MNO4. After 400 cycles, the material MNO7 preserves 100% of capacitance as its initial capacitance. The highly conductive network of nanotablet structure and porous morphologies of MNO7 are most likely responsible for its high capacitive behavior. Such material characteristics deserve a good candidate for electrode material in energy storage applications.

Integrated Battery-Capacitor Electrodes: Pyridinic N-Doped Porous Carbon-Coated Abundant Oxygen Vacancy Mn-Ni-Layered Double Oxide for Hybrid Supercapacitors

Integrating the battery behavior and supercapacitor behavior in a single electrode to obtain better electrochemical performance has been widely researched. However, there is still a lack of research studies on an integrated battery-capacitor supercapacitor electrode (BatCap electrode). In this work, an integrated BatCap electrode porous carbon-coated Mn-Ni-layered double oxide (Mn-Ni LDO-C) was fabricated successfully using controllable heat treatment of polypyrrole-precoated Mn-Ni-layered double hydroxide (Mn-Ni LDH@PPy). This Mn-Ni LDO-C electrode was grown on Ni foam directly and possessed a hierarchical structure that consisted of a pyridinic N (N-6)-doped porous carbon shell and a Mn-Ni LDO core within abundant oxygen vacancies. Benefiting from the synergistic effect of N-6-doped porous carbon and increased oxygen vacancies, Mn-Ni LDO-C exhibited excellent electrochemical performance. The capacity of Mn-Ni LDO-C reached 2.36 C cm^-2 (1478.1 C g^-1) at 1 mA cm^-2 and remained at 92.1% of the initial capacity after 5000 cycles at a current density of 20 mA cm^-2. The aqueous battery-supercapacitor hybrid device Mn-Ni LDO-C//active carbon (Mn-Ni LDO-C//AC) also presented superior cycle stability: it retained 85.3% of the original capacity after 5000 cycles at 2 A g^-1. Meanwhile, Mn-Ni LDO-C//AC could work normally under a wider potential window (2.0 V), so that the device held the highest energy density of 78.2 Wh kg^-1 at a power density of 499.7 W kg^-1 and retained 39.1 Wh kg^-1 at the highest power density of 31.3 kW kg^-1. Two Mn-Ni LDO-C//AC devices connected in series could light a light-emitting diode (LED) bulb easily and keep the LED brightly illuminated for more than 10 min. In general, this work synthesized an integrated BatCap electrode Mn-Ni LDO-C; the integrated electrode exhibited high electrochemical performance, thus has a promising application prospect in the field of energy storage.

Synthesis of Carbon-Supported MnO2 Nanocomposites for Supercapacitors Application

In this study, carbon-supported MnO2 nanocomposites have been prepared using the microwave-assisted heating method followed by two different approaches. The MnO2/C nanocomposite, labeled as sample S1, was prepared directly by the microwave-assisted synthesis of mixed KMnO4 and carbon powder components. Meanwhile, the other MnO2/C nanocomposite sample labeled as S2 was prepared indirectly via a two-step procedure that involves the microwave-assisted synthesis of mixed KMnO4 and MnSO4 components to generate MnO2 and subsequent secondary microwave heating of synthesized MnO2 species coupled with graphite powder. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy have been used for characterization of MnO2/C nanocomposites morphology, structure, and composition. The electrochemical performance of nanocomposites has been investigated using cyclic voltammetry and galvanostatic charge/discharge measurements in a 1 M Na2SO4 solution. The MnO2/C nanocomposite, prepared indirectly via a two-step procedure, displays substantially enhanced electrochemical characteristics. The high specific capacitance of 980.7 F g−1 has been achieved from cyclic voltammetry measurements, whereas specific capacitance of 949.3 F g−1 at 1 A g−1 has been obtained from galvanostatic charge/discharge test for sample S2. In addition, the specific capacitance retention was 93% after 100 cycles at 20 A g−1, indicating good electrochemical stability.

Synthesis of V-shaped MnO2 nanostructure and its composites with reduced graphene oxide for supercapacitor application

A unique V-shaped MnO₂ nanostructure is synthesized with a weak acid (acetic acid) using the microwave-assisted hydrothermal technique. To improve the performance of MnO₂ in supercapacitor applications, its composite was prepared with reduced graphene oxide (rGO), i.e., MnO₂/rGO, with different weight ratios of MnO₂ and rGO. The specific capacitance values of the as-synthesized V-shaped MnO₂ nanostructure and MnO₂/rGO nanocomposite were calculated to be 64.75 and 88.95 F g^-1 at a current density of 0.5 A g^-1, respectively, in 1 M Na₂SO₄ electrolyte. Furthermore, a two-electrode asymmetric supercapacitor device was fabricated using the MnO₂/rGO nanocomposite as a positive electrode and activated carbon as a negative electrode. The device has shown energy densities of 25.14 and 17.95 W h kg^-1 at 0.25 and 1 kW kg^-1 power densities, respectively. These values suggest that the MnO₂/rGO nanocomposite is a promising material for supercapacitor devices.

Mechanism orienting structure construction of electrodes for aqueous electrochemical energy storage systems: a review

Aqueous electrochemical energy storage systems (AEESS) are considered as the most promising energy storage devices for large-scale energy storage. AEESSs, including batteries and supercapacitors, have received extensive attention due to their low cost, eco-friendliness, and high safety. However, the insufficient energy densities of the state-of-the-art AEESSs limit their practical applications which are mainly dominated by the electrochemical performances of individual electrode materials. Understanding the underlying relationship between structures, reaction mechanisms, and performances can further lead to the design and optimization of structures of the electrodes instructively, thereby harvesting favorable performances. This review classified the intrinsic logic of structure-mechanism-performance by taking some prevailing mechanisms with some classical structures of materials as examples. Moreover, some problem-oriented structural engineering strategies are proposed aiming to optimize their performance. Finally, comprehensive structural design engineering and some suggestions for fine modifications of electrode materials at the atomic and molecular levels are proposed to combine the advantages of supercapacitor- and battery-type materials for designing excellent electrode materials for AEESSs.

Low-temperature-synthesized Mn-doped Bi2Fe4O9 as an efficient electrode material for supercapacitor applications

Manganese-doped Bi2Fe4O9, a new material synthesized at a low temperature with a micro-rectangular-shaped particles, is used for supercapacitor applications.

Turning carbon-ZnMn2O4 powder in primary battery waste to be an effective active material for long cycling life supercapacitors: In situ gas analysis

A simple and chemical-free recycled carbon-ZnMn₂O₄ powder (composite) from the spent Zn-carbon batteries is proposed as an effective active material for the supercapacitor. This approach may amplify the economic and environmental benefits of the recycling process. We also synthesized the spherical MnO_x nanoparticles by the calcination followed by the chemical treatment. Recycled composite and the MnO_x nanoparticles were comprehensively characterized. Symmetrical supercapacitors with the composite and the MnO_x nanoparticles show specific capacitances of 118 F g^-1 and 88 F g^-1 at 0.1 A g^-1, respectively. Also, the supercapacitor with the composite offers a specific energy of 8.0Whkg^-1 at 0.1A g^-1 while 4.3Whkg^-1 is obtained for MnO_x nanoparticles. The stable cell potential limits of 1.4 V and 1.2 V were established for the supercapacitors of the composite and MnO_x nanoparticles with the capacitance retention of 83% and 96%, respectively at the end of 100,000 cycles at 2.5Ag^-1. Also, the excellent energy efficiencies of 80% and 72% with the coulombic efficiency of 100% are estimated for the supercapacitors of the composite and the MnO_x nanoparticles, respectively. Finally, in situ gas analysis of the symmetrical supercapacitors are carried out using the differential electrochemical mass spectrometry. The proposed approach may be more economical and the environmentally benign recycling of spent Zn-carbon battery for circular economy and sustainability.

Non-selective synthesis and controllable transformation of parallel MnO2 with hydrogen ions

Acids play a vital role in the controlled synthesis of parallel MnO₂; the appropriate acid groups with highest oxidation state have no effect on the parallel structure, but acid groups with reducibility can promote its formation.