Interconnected network of ultrafine MnO2 nanowires on carbon cloth with weed-like morphology for high-performance supercapacitor electrodes

Facile Synthesis of Polypyrrole/MnO2/Carbon Cloth Composites for Supercapacitor Electrodes

In the development of flexible smart electronics, fabricating electrodes with optimized architectures to achieve superior electrochemical performance remains a significant challenge. This study presents a two-step synthesis and characterization of a polypyrrole (PPy)-MnO2/carbon cloth (CC) nanocomposite. The MnO2/CC substrate was first prepared via the hydrothermal method, followed by uniform PPy coating through vapor-phase polymerization in the presence of an oxidizing agent. Electrochemical measurements revealed substantial enhancement in performance, with the specific capacitance increasing from 123.1 mF/cm2 for the MnO2/CC composite to 324.5 mF/cm2 for the PPy/MnO2/CC composite at a current density of 2.5 mA/cm2. This remarkable improvement can be attributed to the synergistic effects between the conductive PPy polymer and MnO2/CC substrate and the formation of additional ion transport channels facilitated by the PPy coating. This work provides valuable insights for designing high-performance electrode materials and advances the development of composite-based energy storage devices.

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.

High-Valence-Manganese Driven Strong Anchoring of Iridium Species for Robust Acidic Water Oxidation

Designing an efficient and durable electrocatalyst for the sluggish anodic oxygen evolution reaction (OER) has been the primary goal of using proton exchange membrane electrolyzer owing to the highly acidic and oxidative environment at the anode. In this work, it is reported that high-valence manganese drives the strong anchoring of the Ir species on the manganese dioxide (MnO2 ) matrix via the formation of an Mn-O-Ir coordination structure through a hydrothermal-redox reaction. The iridium (Ir)-atom-array array is firmly anchored on the Mn-O-Ir coordination structure, endowing the catalyst with excellent OER activity and stability in an acidic environment. Ir-MnO2 (160)-CC shows an ultralow overpotential of 181 mV at j = 10 mA cm-2 and maintains long-term stability of 180 h in acidic media with negligible decay, superior to most reported electrocatalysts. In contrast, when reacting with low-valence MnO2 , Ir species tend to aggregate into IrOx nanoparticles, leading to poor OER stability. Density functional theory (DFT) calculations further reveal that the formation of the Mn-O-Ir coordination structure can optimize the adsorption strength of *OOH intermediates, thus boosting the acidic OER activity and stability.

Preparation of MnO2-Carbon Materials and Their Applications in Photocatalytic Water Treatment

Water pollution is one of the most important problems in the field of environmental protection in the whole world, and organic pollution is a critical one for wastewater pollution problems. How to solve the problem effectively has triggered a common concern in the area of environmental protection nowadays. Around this problem, scientists have carried out a lot of research; due to the advantages of high efficiency, a lack of secondary pollution, and low cost, photocatalytic technology has attracted more and more attention. In the past, MnO₂ was seldom used in the field of water pollution treatment due to its easy agglomeration and low catalytic activity at low temperatures. With the development of carbon materials, it was found that the composite of carbon materials and MnO₂ could overcome the above defects, and the composite had good photocatalytic performance, and the research on the photocatalytic performance of MnO₂-carbon materials has gradually become a research hotspot in recent years. This review covers recent progress on MnO₂-carbon materials for photocatalytic water treatment. We focus on the preparation methods of MnO₂ and different kinds of carbon material composites and the application of composite materials in the removal of phenolic compounds, antibiotics, organic dyes, and heavy metal ions in water. Finally, we present our perspective on the challenges and future research directions of MnO₂-carbon materials in the field of environmental applications.

Lamellar structured Ni3P2O8: first-ever use to design 1.8 V operated flexible all-solid-state symmetric supercapacitor

Increasing demand for microelectronic devices necessitates the development of highly flexible energy storage technologies with a wide operating voltage. Thus, flexible electrodes and their devices with the requisite mechanical and electrochemical characteristics have prime importance. In this regard, the present article demonstrates the feasibility of designing a flexible all-solid-state supercapacitor using a chemically grown Ni₃P₂O₈ lamellar microstructured electrode embedded with carboxy methyl cellulose-Na₂SO₄ (CMC-Na₂SO₄) gel electrolyte. The formed symmetric device impressively exhibited a maximum working voltage window of 1.8 V with a high specific energy of 44.7 W h kg^-1 and specific power of 3.3 kW kg^-1 along with prolonged cycle life. Also, the device's high deformation tolerance (95%) when bent at 170° with a flashing light-emitting diode (LED) working demonstration showcases its viability for advanced flexible energy storage applications.

Sodium Pre-Intercalation-Based Na3-δ-MnO2@CC for High-Performance Aqueous Asymmetric Supercapacitor: Joint Experimental and DFT Study

Electrochemical energy storage devices are ubiquitous for personal electronics, electric vehicles, smart grids, and future clean energy demand. SCs are EES devices with excellent power density and superior cycling ability. Herein, we focused on the fabrication and DFT calculations of Na₃-δ-MnO₂ nanocomposite, which has layered MnO₂ redox-active sites, supported on carbon cloth. MnO₂ has two-dimensional diffusion channels and is not labile to structural changes during intercalation; therefore, it is considered the best substrate for intercalation. Cation pre-intercalation has proven to be an effective way of increasing inter-layered spacing, optimizing the crystal structure, and improving the relevant electrochemical behavior of asymmetric aqueous supercapacitors. We successfully established Na⁺ pre-intercalated δ-MnO₂ nanosheets on carbon cloth via one-pot hydrothermal synthesis. As a cathode, our prepared material exhibited an extended potential window of 0-1.4 V with a remarkable specific capacitance of 546 F g^-1(300 F g^-1 at 50 A g^-1). Moreover, when this cathode was accompanied by an N-AC anode in an asymmetric aqueous supercapacitor, it illustrated exceptional performance (64 Wh kg^-1 at a power density of 1225 W kg^-1) and incomparable potential window of 2.4 V and 83% capacitance retention over 10,000 cycles with a great Columbic efficiency.

Electrochemical Performance of MnO2/Graphene Flower-like Microspheres Prepared by Thermally-Exfoliated Graphite

To enhance the electrochemical performance of MnO₂/graphene composite, herein, thermally-exfoliated graphite (TE-G) is adopted as a raw material, and a hydrothermal reaction is conducted to achieve the exfoliation of TE-G and the loading of MnO₂ nanosheets. Through optimizing the TE-G/KMnO₄ ratio in the redox reaction between carbon and KMnO₄, flower-like MnO₂/G microspheres (MnO₂/G-10) are obtained with 83.2% MnO₂ and 16.8% residual graphene. Meanwhile, corresponding MnO₂/rGO composites are prepared by using rGO as raw materials. Serving as a working electrode in a three-electrode system, MnO₂/G-10 composite displays a specific capacitance of 500 F g⁻¹ at 1 A g⁻¹, outstanding rate performance, and capacitance retention of 85.3% for 5,000 cycles. The performance is much better than that of optimized MnO₂/rGO composite. We ascribe this to the high carbon fraction in TE-G resulting in a high fraction of MnO₂ in composite, and the oxygen-containing groups in rGO reduce the resulting MnO₂ fraction in the composite. The superior electrochemical performance of MnO₂/G-10 is dependent on the hierarchical porous structure constructed by MnO₂ nanosheet arrays and the residual graphene layer in the composite. In addition, a supercapacitor assembled by TE-G negative electrode and MnO₂/G positive electrode also exhibits superior performance. In consideration of the low cost of raw materials, the MnO₂/G composite exhibits great application potential in the field of supercapacitors.

CoMnO2-Decorated Polyimide-Based Carbon Fiber Electrodes for Wire-Type Asymmetric Supercapacitor Applications

In this work, we report the carbon fiber-based wire-type asymmetric supercapacitors (ASCs). The highly conductive carbon fibers were prepared by the carbonized and graphitized process using the polyimide (PI) as a carbon fiber precursor. To assemble the ASC device, the CoMnO₂-coated and Fe₂O₃-coated carbon fibers were used as the cathode and the anode materials, respectively. Herein, the nanostructured CoMnO₂ were directly deposited onto carbon fibers by a chemical oxidation route without high temperature treatment in presence of ammonium persulfate (APS) as an oxidizing agent. FE-SEM analysis confirmed that the CoMnO₂-coated carbon fiber electrode exhibited the porous hierarchical interconnected nanosheet structures, depending on the added amount of APS, and Fe₂O₃-coated carbon fiber electrode showed a uniform distribution of porous Fe₂O₃ nanorods over the surface of carbon fibers. The electrochemical properties of the CoMnO₂-coated carbon fiber with the concentration of 6 mmol APS presented the enhanced electrochemical activity, probably due to its porous morphologies and good conductivity. Further, to reduce the interfacial contact resistance as well as improve the adhesion between transition metal nanostructures and carbon fibers, the carbon fibers were pre-coated with the Ni layer as a seed layer using an electrochemical deposition method. The fabricated ASC device delivered a specific capacitance of 221 F g^-1 at 0.7 A g^-1 and good rate capability of 34.8% at 4.9 A g^-1. Moreover, the wire-type device displayed the superior energy density of 60.2 Wh kg^-1 at a power density of 490 W kg^-1 and excellent capacitance retention of 95% up to 3000 charge/discharge cycles.

In Situ Growing Double-Layer TiO2 Nanorod Arrays on New-Type FTO Electrodes for Low-Concentration NH3 Detection at Room Temperature

A novel double-layer TiO₂ nanorod array (NRA) gas sensor for room-temperature detection of NH₃ was fabricated by employing etched fluorine-doped tin dioxide (FTO) glass as the in situ growing substrate and the new-type gas-sensing electrode via the facile droplet-coating and hydrothermal methods. Due to the synergistic effect of forces, special double-layer TiO₂ NRAs with a cross-linked and bridgelike structure is formed, in which adequate point junctions can be generated to construct self-assembled electron pathways required for gas-sensing tests. Gas-sensing tests indicate that all samples obtained at different growth times have an excellent gas-sensing response to low-concentration NH₃ at room temperature. Among them, the TiO₂ NRAs obtained at 6 h (S2) exhibit the highest gas-sensing response to 100 ppm NH₃ with a value of 102%. In addition, the growth mechanism, the gas reaction mechanism, and the effect of humidity on the gas-sensing performance are also discussed in the present paper.

Multidimensional structure of CoNi2S4 materials: structural regulation promoted electrochemical performance in a supercapacitor

Multidimensional architectures of CoNi2S4 electrode materials are rationally designed by engineering the surface structure toward that of high-performance supercapacitors. The fabrication of a special morphology is highly dependent on the synergistic effect between the guidance of Co-Ni precursor arrays and a subsequent sulfidation process. The unparalleled CoNi2S4 electrode materials (NS-3) deliver a significantly enhanced specific capacitance (3784.6 F g-1 at 3 A g-1), accompanied by an extraordinary rate capability (2932.3 F g-1 at 20 A g-1) and excellent cycling life. The outstanding supercapacitor performance stated above stems from the advantages of a multidimensional structure generated by crosslinking 2D microsheets/1D nanowires/2D ultrathin nanosheets; this structure supplies additional efficient active sites and a large contact area at the electrode-electrolyte interface, providing faster transport kinetics for electrons and ions. For practical applications, asymmetric devices based on an NS-3 positive electrode and active carbon negative electrode exhibit a high energy density of 38.5 W h kg-1 accompanied by a power density of 374.9 W kg-1 (22 W h kg-1 at 7615.4 W kg-1). The above results indicate that the design of multidimensional Co-Ni-S materials is an effective strategy to achieve a high-performance supercapacitor.

Cobalt-Doped Porous Carbon Nanosheets Derived from 2D Hypercrosslinked Polymer with CoN₄ for High Performance Electrochemical Capacitors

Cobalt-doped graphene-coupled hypercrosslinked polymers (Co-GHCP) have been successfully prepared on a large scale, using an efficient RAFT (Reversible Addition-Fragmentation Chain Transfer Polymerization) emulsion polymerization and nucleophilic substitution reaction with Co (II) porphyrin. The Co-GHCP could be transformed into cobalt-doped porous carbon nanosheets (Co-GPC) through direct pyrolysis treatment. Such a Co-GPC possesses a typical 2D morphology with a high specific surface area of 257.8 m² g^-1. These intriguing properties of transition metal-doping, high conductivity, and porous structure endow the Co-GPC with great potential applications in energy storage and conversion. Utilized as an electrode material in a supercapacitor, the Co-GPC exhibited a high electrochemical capacitance of 455 F g^-1 at a specific current of 0.5 A g^-1. After 2000 charge/discharge cycles, at a current density of 1 A g^-1, the specific capacitance increased by almost 6.45%, indicating the excellent capacitance and durability of Co-GPC. These results demonstrated that incorporation of metal porphyrin into the framework of a hypercrosslinked polymer is a facile strategy to prepare transition metal-doped porous carbon for energy storage applications.

Ultrafine MnO2 nanowires grown on RGO-coated carbon cloth as a binder-free and flexible supercapacitor electrode with high performance

Reduced graphene oxide coated carbon cloth has been used as a substrate for the growth of ultrafine MnO2 nanowires (CC/RGO/MnO2), forming binder-free and flexible supercapacitor electrode materials. The experimental results indicate that a maximum area-specific capacitance of 506.8 mF cm-2 was gained from the CC/RGO/MnO2 electrode at the current density of 0.128 mA cm-2. Furthermore, the electrode exhibits excellent cycling stability (98.6% specific capacitance was still retained after 10 000 galvanostatic charge-discharge (GCD) tests when the current density was 1.28 mA cm-2). What's more, the area-specific capacitance of the CC/RGO/MnO2 electrode was hardly changed, when the electrode was operated under bending mechanical conditions. In addition, the charge storage performance and mechanism of the MnO2 nanostructures was discussed.