Flexible MnO2 Research Articles

Boosting the pseudocapacitance of BiFeO3 by Zn doping for flexible battery-supercapacitor hybrid devices

Perovskite BiFeO3 (BFO) as a type of battery-type electrode materials, usually suffers from poor electrolyte ion transport in the BFO crystal. We propose a novel strategy of Zn doping to improve the ion transport and boost the faradaic pseudocapacitance of BFO for flexible battery-supercapacitor hybrid (BSH) devices. The Zn-doped BFO (Z-BFO-1) with the low Zn doping content, can maintain the crystal structure of BFO and the uniform distributions of elements. The oxygen vacancy content can be increased from BFO to Z-BFO-1, reflecting the influence of the Zn doping on the crystal structure of BFO. The Z-BFO-1 electrode with the stable crystal structure in the charge/discharge process, can provide the highest specific capacitance (223 F g−1 at 0.2 A/g) and the largest Li+ diffusion coefficient (2.386 × 10−11 cm2 s−1) among these BFO-based electrodes with different Zn doping contents. The first-principles calculations reveal that the Zn doping in BFO can significantly enhance the built-in electric fields and greatly lower the Li+ migration energy barriers (from 2.08 eV to 1.43 eV). This flexible MnO2//Z-BFO-1 BSH device with the high energy density (37.5 Wh kg−1 at 0.23 kW kg−1), opens up a new avenue for developing high-performance electrochemical energy storage devices.

In-situ electronic modulation of ultra-high-capacity S-modified Cu/Cu2O electrodes for energy storage applications

Due to the modification of anions, an electron redistribution occurs at the metal ions can affect the electronic structure, and induce excellent specific capacity. Herein, we report an effective and low time-consuming method by in-situ wet chemical reduction at room temperature to construct S-modified Cu/Cu2O negative electrode material. Moreover, the sulfur can occupy partial O sites in Cu2O to play a crucial role in the electronic structure of the material, demonstrated by DFT calculation, XRD, XPS and XAS measurements. The prepared S-Cu/Cu2O samples exhibit excellent electrochemical performance with high specific capacity of 669 mAh·g−1 at 1 A·g−1, even 450 mAh·g−1 at 10 A·g−1. When the materials are composed as pseudo capacity-type cathode//battery-like anode (MnO2//S-Cu/Cu2O), and (+) battery-type//battery-type (-) (Ni-Cu hydroxide/Cu(OH)2/CF//S-Cu/Cu2O) hybrid capacitors, they show the energy density of 47.7 and 147.3 Wh·kg−1 at the power density of 636.2 and 800 kW·kg−1, respectively. Otherwise, the flexible MnO2//S-Cu/Cu2O hybrid capacitor is assembled, which also exhibits good performance at different bending conditions. This work can provide a simple method to prepare the electrode materials via in situ anion modification for high-energy density battery-like energy storage systems.

Flexible Ammonium-Ion Pouch Cells Based on a Tunneled Manganese Dioxide Cathode.

Aqueous ammonium-ion (NH4+) batteries are becoming the competitive energy storage candidate on account of their safety, affordability, sustainability, and intrinsically peculiar properties. Herein, an aqueous NH4+-ion pouch cell is investigated based on a tunneled manganese dioxide (α-MnO2) cathode and a 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) anode. The MnO2 electrode possesses a high specific capacity of ∼190 mA h g-1 at 0.1 A g-1 and displays excellent long cycling performance after 50,000 cycles in 1 M (NH4)2SO4, which outperforms the most reported ammonium-ion host materials. Besides, a solid-solution behavior is revealed about the migration of NH4+ in the tunnel-like α-MnO2. The battery displays a splendid rate capacity of 83.2 mA h g-1 even at 10 A g-1. It also exhibits a high energy density of ∼78 W h kg-1 as well as a high power density of ∼8212 W kg-1 (based on the mass of MnO2). What is more, the flexible MnO2//PTCDA pouch cell based on the hydrogel electrolyte shows excellent flexibility and good electrochemical properties. The topochemistry results of MnO2//PTCDA point to the potential practicability of ammonium-ion energy storage.

Fabrication of Flexible All-Solid-State Asymmetric Supercapacitor Device via Full Recycling of Heated Tobacco Waste Assisted by PLA Gelation Template Method.

In this study, a flexible all-solid-state asymmetric supercapacitor (FASC) device has been successfully fabricated via full recycling of heated tobacco waste (HTW). Tobacco leaves and cellulose acetate tubes have been successfully carbonized (HTW-C) and mixed with metal oxides (MnO2 and Fe3O4) to obtain highly active materials for supercapacitors. Moreover, poly(lactic acid) (PLA) filters have been successfully dissolved in an organic solvent and mixed with the as-prepared active materials using a simple paste mixing method. In addition, flexible MnO2- and Fe3O4-mixed HTW-C/PLA electrodes (C-MnO2/PLA and C-Fe3O4/PLA) have been successfully fabricated using the drop-casting method. The as-synthesized flexible C-MnO2/PLA and C-Fe3O4/PLA electrodes have exhibited excellent electrical conductivity of 378 and 660 μS cm-1, and high specific capacitance of 34.8 and 47.9 mF cm-2 at 1 mA cm-2, respectively. A practical FASC device (C-MnO2/PLA//C-Fe3O4/PLA) has been assembled by employing the C-MnO2/PLA as the positive electrode and C-Fe3O4/PLA as the negative electrode. The as-prepared FASC device showed a remarkable capacitance of 5.80 mF cm-2 at 1 mA cm-2. Additionally, the FASC device manifests stable electrochemical performance under harsh bending conditions, verifying the superb flexibility and sustainability of the device. To the best of our knowledge, this is the first study to report complete recycling of heated tobacco waste to prepare the practical FASC devices. With excellent electrochemical performance, the experiments described in this study successfully demonstrate the possibility of recycling new types of biomass in the future.

Facile and green synthesis of nanocellulose with the assistance of ultraviolet light irradiation for high-performance quasi-solid-state zinc-ion batteries

Benefiting from excellent mechanical properties, large surface area, rich hydroxyl groups, good sustainability, etc., nanocellulose is highly promising for various applications. However, intense chemical treatment and long-term processing are usually required to fabricate nanocellulose. Herein, a new synthesis method of nanocellulose is developed by using ultraviolet light irradiation-assisted delignification and subsequent sonification. This method is more cost-effective, time-saving, and environmentally benign compared to most of previously reported synthesis methods of nanocellulose. The obtained nanocellulose contains a small amount of lignin, which is unfavorable for high-temperature stability and optimal transparency. However, a small amount of lignin is beneficial to mechanical properties and in-water stability. With this nanocellulose, flexible MnO2 cathode film and hydrogel electrolyte are constructed and a quasi-solid-state zinc-ion battery is assembled. The battery exhibits 233.3 mAh g−1 after 1000 cycles at 1 A g−1 and 20 ℃. And more than half of that capacity can be maintained at –20 ℃. The battery also possesses great rate capability and good endurance to external forces. This work provides new insights into the synthesis and application of nanocellulose.

Preparation of MnO2 Loaded Hydrothermal Carbon-coated Electrospun PAN Fiber Membranes for Highly Efficient Adsorption and Separation of Cationic Dye

Hydrothermal carbonaceous materials and MnO2 have been proved to be promising adsorbents to remove organic dyes from wastewater. In this study, flexible MnO2 loaded hydrothermal carbon-coated electrospun polyacrylonitrile(AC/MnO2/PAN) fiber membranes were fabricated by a facile one-step hydrothermal method and activated by NaOH solution. The composite fibers exhibited large adsorption capacity toward cationic dyes and excellent mechanical properties. The adsorption performance can be fitted well with pseudo-second-order model and Langmuir isotherm model. The maximum adsorption for methylene blue(MB), methyl violet(MV) and malachite green(MG) are 1173.27, 1106.31 and 1129.89 mg/g, respectively, according to Langmuir fitting. The AC/MnO2/PAN fiber membrane also showed satisfactory performances for selective adsorption and recyclability. In addition, based on selective adsorption, the AC/MnO2/PAN fiber membranes that are repulsive to the anionic dye methyl orange(MO) can separate the MB/MO mixture solution by dynamic filtration. Thus, this work not only provides a facile strategy to fabricate large capacity adsorbents, but also demonstrates the potential applications in the dye wastewater treatment field.

Porous MnO2–CNTs–Cellophane Nanocomposite for High-Voltage Flexible Supercapacitors

Flexible MnO2–CNTs–cellophane electrode was easily fabricated via addition of NaHCO3 in matrix of manganese dioxide-carbon nanotubes-cellophane composite followed by selective etching of NaHCO3 in acidic solution to produce a porous network structure as result of CO2 (g) bubbling. Under the optimized mass loading, the flexible-porous electrode presented favorite electrochemical capacitance behavior with the areal capacitance of 121 and 55.5 mF cm−2 at the current density of 0.6 mA cm−2 in 1.0 M H2SO4 and Na2SO4 electrolytes, respectively. A symmetric all-solid-state supercapacitor assembled with the flexible MnO2/CNTs/cellophane electrode showed a wide working voltage (2.0 V), a high areal capacitance of 82.5 mF cm−2 at a current density of 2.0 mA cm−2, favorite flexibility and good cycling stability (83% after 2000 cycles at a current density of 2.0 mA cm−2). Therefore, such a simple and scalable procedure to produce flexible supercapacitor device based MnO2–CNTs composite is offering for future flexible energy storage systems. Flexible solid-state supercapacitor device based on MnO2–CNTs–cellophane electrode.

Electrodeposition of silver (Ag) nanoparticles on MnO2 nanorods for fabrication of highly conductive and flexible paper electrodes for energy storage application

Metal oxide based electrodes are attractive for energy storage applications with limited characteristics of flexibility due to inherent rigid structure. However, incorporation of flexible insulating matrix within metal oxide composites result in poor electrically conductive and energy storage characteristics. This study presents the fabrication of flexible MnO2 based composite electrodes prepared by incorporation of lignocelluloses (LC) fibers, directly collected from a self-growing plant, Monochoria Vaginalis. Furthermore electrodeposition of silver (Ag) nanoparticles was performed on LC/MnO2 in potentiostatic mode to address the electrically conductive characteristics. Morphology, structural, conductive and energy storage properties of fabricated electrodes are analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), impedance analyzer and potentiostat, respectively. SEM images clearly indicate the deposition of Ag nanoparticles on MnO2 nanorods embedded in LC fibers whereas FTIR results confirm the bonding of the functional groups. Cyclic voltammetry measurements showed efficient kinetics of LC/MnO2 after electrodeposition of Ag nanoparticles. The effects on electrical properties associated with blending MnO2 nanorods in lignocelluloses fibers and Ag deposition on MnO2 in LC/MnO2 are explored in wide frequency range between 10 Hz and 5 MHz. However, deposition of Ag nanoparticles on MnO2 nanorods surfaces acts as a conductive path and reduces the associated resistance. Incorporated flexibility in rigid structure of MnO2 and further improvements in conductive and energy storage characteristics will open the possibilities to be used as electrode in modern bendable energy storage devices.

MnO2 nanoparticles anchored on carbon nanotubes with hybrid supercapacitor-battery behavior for ultrafast lithium storage

Developing hybrid supercapacitor-battery energy storage devices for applications in electric vehicles is attractive because of their high energy density and short charge/discharge time. In this study, flexible MnO2 nanoparticle-coated air-oxidized carbon nanotube (MnO2/aCNT) electrodes are fabricated by the in situ redox reaction of KMnO4 and aCNTs at room temperature. The MnO2 nanoparticles have diameters of ∼10 nm. There is a strong chemical interaction between the MnO2 active material and aCNTs as a result of the Mn–O–C linkage. The flexible aCNT network can alleviate the strain from the MnO2 volume change and maintain the electrode integrity during rapid charge/discharge. The aCNT framework also provides a continuous and rapid electron pathway and ensures uniform dispersion of the MnO2 nanoparticles. The presence of MnO2 nanoparticles provides short pathways for Li-ion diffusion and allows interfacial capacitive lithium storage for ultrafast and reversible lithium storage. We report the best high-current performance to date for MnO2/C electrodes, of 395.8 mA h g−1 at 10 A g−1, and 630.2 mA h g−1 after 150 cycles at 2 A g−1. The excellent electrochemical performance, combined with the capacitive dominating process of the electrode, will further the design of high-performance hybrid supercapacitor-battery energy storage devices.

Carbon Quantum Dot-Induced MnO2 Nanowire Formation and Construction of a Binder-Free Flexible Membrane with Excellent Superhydrophilicity and Enhanced Supercapacitor Performance.

Manganese oxides (MnO2) are regarded as typical and promising electrode materials for supercapacitors. However, the practical electrochemical performance of MnO2 is far from its theoretical value. Nowadays, numerous efforts are being devoted to the design and preparation of nanostructured MnO2 with the aim of improving its electrochemical properties. In this work, ultralong MnO2 nanowires were fabricated in a process induced by carbon quantum dots (CQDs); subsequently, a binder-free flexible electrode membrane was easily obtained by vacuum filtration of the MnO2 nanowires. The effects of the CQDs not only induced the formation of one-dimensional nanostructured MnO2, but also significantly improved the wettability between electrode and electrolyte. In other words, the MnO2 membrane demonstrated a superhydrophilic character in aqueous solution, indicating the sufficient and abundant contact probability between electrode and electrolyte. The binder-free flexible MnO2 electrode exhibited a preeminent specific capacitance of 340 F g-1 at 1 A g-1; even when the current density reached 20 A g-1, it still maintained 260 F g-1 (76% retention rate compared to that at 1 A g-1). Moreover, it also showed good cycling stability with 80.1% capacity retention over 10 000 cycles at 1 A g-1. Furthermore, an asymmetric supercapacitor was constructed using the MnO2 membrane and active carbon as the positive and negative electrodes, respectively, which exhibited a high energy density of 33.6 Wh kg-1 at 1.0 kW kg-1, and a high power density of 10 kW kg-1 at 12.5 Wh kg-1.

Fabrication of high performance flexible all-solid-state asymmetric supercapacitors with a three dimensional disc-like WO3/stainless steel electrode

The schematic of steps involved in fabrication of flexible MnO2//WO3 ASCs device.