MnO2 Nanowires Research Articles

Electrochemically Fabricated Superhydrophilic/Superaerophobic Manganese Oxide Nanowires at Discontinuous Solid–Liquid Interfaces for Enhanced Oxygen Evolution Performances

AbstractThe design of an electrode surface is critical to the oxygen evolution reaction (OER) during electrochemical water splitting since the catalytic activity depends strongly on surface characteristics, such as the coating uniformity of the catalysts, electrolyte wetting, and the gas‐bubble release ability. Here, nonprecious‐metal electrocatalysts (MnO nanowires) are electrochemically deposited on the surface of a porous gold microgrid. The discontinuous solid–liquid contact lines, which are formed by the microgrids during the liquid‐phase electrochemical reaction, generate MnO nanowires with high coating uniformity. The micro/nanostructure of the electrode induces a superhydrophilic surface, which facilitates the wetting of the alkaline electrolyte and increases the electrochemical active surface area. Simultaneously, the underwater superaerophobicity of the electrode promotes the release of the oxygen products, thus reducing the occupation of the catalytic sites by the gas bubbles. The synergistic effect of electrolyte wetting and gas release ensures that this superhydrophilic/superaerophobic electrode exhibits a current density of 10 mA cm−2 for the OER at an overpotential of 530 mV in 0.1 m KOH, placing the catalyst among the best MnO catalysts for OER. This work avails a new basis for synergistically optimizing the synthesis methods (electrolyte wetting and gas‐bubble release) toward high‐performance OER electrodes.

Investigation on the effect of metal contacts on the vertical MnO2 nanowire array-based Schottky barrier diodes

Investigation on the effect of metal contacts on the vertical MnO2 nanowire array-based Schottky barrier diodes

Fabrication of MnO2 nanowires and their nanohybrid with flat conductive matrix for the treatment of industrial effluents

In recent times, nanostructured semiconductive materials and nanohybrid with flat (2D) MXene sheets have gained considerable attention for photocatalytic applications. Here, we fabricated MnO2 nanowires (NWs, 1D) and their nanohybrid with MXene, as an innovative photocatalyst, to remove organic pollutants (organic dyes) and bacteria from industrial effluents. Indeed, MXene has excellent surface properties, owing to its flat structure. However, it's higher affinity to restack and oxidize is the problem that masks its other inherent features. We developed an innovative design to improve the stability of MXene and to reduce the resistivity and photocorrosion of semiconductive photocatalysts. The crystalline structure, morphology, specific surface area, thermal stability, and nanohybrid formation between MnO2 and MXene have been analyzed and confirmed via well-established conventional and advanced techniques. The prepared materials' photocatalytic and antimicrobial properties were evaluated under solar illumination using crystal violet (CV) dye and a Staphylococcus aureus(S.aureus) bacterial strain, respectively. Compared to pure MnO2 and MXene/MnO2 nanohybrid photocatalysts, H2O2-supported MXene/MnO2 nanohybrid demonstrated significantly greater photocatalytic activity for CV dye elimination. After 50 min of continuous illumination, the MXene/MnO2@H2O2 photocatalyst demonstrated approximately 91.5% dye degradation at a rate constant (0.045 min−1) higher than MnO2 (0.025 min−1) and MXene/MnO2 (0.029 min−1). The current work demonstrates that the MXene/MnO2 nanohybrid photocatalyst is capable of photodegrading dyes efficiently and inhibiting the rapid growth of microbes found in industrial discharges.

Oxidative degradation of aqueous organic contaminants over shape-tunable MnO2 nanomaterials via peroxymonosulfate activation

Cryptomelane-type MnO2 nanomaterials with a-crystalline phase were prepared by heat treatment of the mixture of MnCO3 and potassium oxalate followed by acid treatment. The evolution of the crystalline phase and morphology from MnCO3 to cryptomelane was investigated by XRD, BET, SEM and TEM. Moreover, MnO2 in nanoparticle, nanorod and nanofiber shapes could be controlled by adjusting the reaction time and temperature in the acid-treatment step. MnO2 nanofibers demonstrated promoted catalytic activity and recyclability for the oxidative degradation of various organic dyes, tetracyclines and bisphenol A via peroxymonosulfate (PMS) activation. About 99% of RhB, AO7, MB, red 2 and bisphenol A at a concentration of 20–50 mg/L could be degraded over MnO2 nanofibers within 12 min. Furthermore, antibiotics, like tetracycline, chlortetracycline and oxytetracycline, and bisphenol A could be mineralized efficiently, and 69–81% TOC removal was obtained. Compared to MnO2 nanowires synthesized by the traditional method with KMnO4, MnO2 nanofibers showed enhanced surface area (102 m2/g), more labile lattice oxygen species and higher oxygen vacancy content, which might be responsible for the superior catalytic performances. The radical quenching test and EPR analysis proved that radical (O2−, SO4− and OH) and non-radical (1O2) processes both existed, and the latter dominantly contributed to the degradation. Based on kinetic study, the activation energy of MnO2 nanofibers/PMS for RhB degradation was only 10.55 kJ/mol, which was lower than that of MnO2 nanowires (16.80 kJ/mol). This study not only offered a new, simple and economical protocol for the scaled-up synthesis of nano-scale MnO2 materials, but also demonstrated its potential in water remediation.

Nitrogen-doped carbon–cobalt-modified MnO nanowires as cathodes for high-performance lithium sulfur batteries

The shuttle effect and slow redox reaction kinetics of Li–S batteries due to the dissolution of lithium polysulfides (LiPSs) during charging and discharging lead to a remarkable decrease in the cycle life and sulfur utilization of Li–S batteries. In this paper, MnO 2 nanowires were embedded in ZIF-67 by polyvinylpyrrolidone modification and then carbonized at high temperature to obtain N -doped carbon (NC)-Co@MnO composites with high specific surface area and mesoporous structure for high sulfur loading. This conductive network structure provides a strong conductive pathway for LiPSs, promotes the adsorption of LiPSs, effectively facilitates electron transport, and enhances the trapping ability of LiPSs in the cathode. The prepared NC-Co@MnO@S cathode has excellent electrochemical performance and stable charge–discharge performance because of the combination of the high conductivity of NC-Co with high specific surface area, as well as the strong interaction between MnO and polysulfide. The initial discharge specific capacity was 1175 mAh/g. The NC-Co@MnO@S composite can still maintain a stable discharge capacity of 700 mAh/g after 200 cycles at a current density of 0.2 C with a capacity retention rate of 72%. This composite material has great promise for application as a low-cost, high-performance electrode for Li–S batteries.

Nest-Like MnO2 Nanowire/Hierarchical Porous Carbon Composite for High-Performance Supercapacitor from Oily Sludge.

In the aim to go beyond the performance tradeoffs of classic electric double-layer capacitance and pseudo-capacitance, composites made out of carbon and pseudo-capacitive materials have been a hot-spot strategy. In this paper, a nest-like MnO2 nanowire/hierarchical porous carbon (HPC) composite (MPC) was successfully fabricated by a controllable in situ chemical co-precipitation method from oily sludge waste. Due to the advantages of high surface area and fast charge transfer for HPC as well as the large pseudo-capacitance for MnO2 nanowires, the as-prepared MPC has good capacitance performance with a specific capacitance of 437.9 F g−1 at 0.5 A g−1, favorable rate capability of 79.2% retention at 20 A g−1, and long-term cycle stability of 78.5% retention after 5000 cycles at 5 A g−1. Meanwhile, an asymmetric supercapacitor (ASC) was assembled using MPC as the cathode while HPC was the anode, which exhibits a superior energy density of 58.67 W h kg−1 at the corresponding power density of 498.8 W kg−1. These extraordinary electrochemical properties highlight the prospect of our waste-derived composites electrode material to replace conventional electrode materials for a high-performance supercapacitor.

Ultrafine Mn3O4 nanowires synthesized by colloidal method as electrode materials for supercapacitors with a wide voltage range

Manganese oxide is considered an ideal pseudo-capacitive electrode material for supercapacitors due to its low cost, environmental friendliness and large theoretical capacity. However, it is difficult to obtain manganese electrodes with a high specific capacitance and a large voltage range. In this study, ultrafine Mn3O4 nanowires with an average diameter of 4.0 nm were synthesized using a colloidal method. They have a large specific surface area of 175.1 m2 g−1, and can provide numerous active sites to enhance their specific capacitances. They also show a large pore volume of 0.7960 cm3 g−1, which can provide essential channels for ion transport during charging and discharging processes. The supercapacitor electrode made of these ultrafine Mn3O4 nanowires exhibits a predominant surface capacitive behavior during charge/discharge processes, and achieves a large specific capacitance of 433.1 F g−1 at a current density of 0.5 A g−1 with a very wide voltage range from -0.5 to 1.1 V in 1 M Na2SO4 electrolyte. An asymmetric supercapacitor (ASC) was assembled using a cathode electrode made of these ultrafine Mn3O4 nanowires and an active carbon (AC) anode electrode, and a high energy density of 26.68 Wh kg−1 at a power density of 442 W kg−1 was achieved. The ASC showed a good cycling stability, and its capacitance value was still maintained at 75.8% after 64,000 charge/discharge cycles.

Influence of nickel doping on MnO2 nanoflowers as electrocatalyst for oxygen reduction reaction

Doping is promising strategy for the alteration of nanomaterials to enhance their optical, electrical, and catalytic activities. The development of electrocatalysts for oxygen reduction reactions (ORR) with excellent activity, low cost and durability is essential for the large-scale utilization of energy storage devices such as batteries. In this study, MnO2 and Ni-doped MnO2 nanowires were prepared through a simple co-perception technique. The influence of nickel concentration on electrochemical performance was studied using linear sweep voltammetry and cyclic voltammetry. The morphological, thermal, structural, and optical properties of MnO2 and Ni-doped MnO2 nanowires were examined by SEM, ICP-OES, FT-IR, XRD, UV–Vis, BET and TGA/DTA. Morphological analyses showed that pure MnO2 and Ni-doped MnO2 had flower-like and nanowire structures, respectively. The XRD study confirmed the phase transformation from ε to α and β phases of MnO2 due to the dopant. It was also noted from the XRD studies that the crystallite sizes of pure MnO2 and Ni-doped MnO2 were in the range of 2.25–6.6 nm. The band gaps of MnO2 and 0.125 M Ni-doped MnO2 nanoparticles were estimated to be 2.78 and 1.74 eV, correspondingly, which can be seen from UV–Vis. FTIR spectroscopy was used to determine the presence of functional groups and M–O bonds (M = Mn, Ni). The TGA/TDA examination showed that Ni-doping in MnO2 led to an improvement in its thermal properties. The cyclic voltammetry results exhibited that Ni-doped MnO2 nanowires have remarkable catalytic performance for ORR in 0.1 M KOH alkaline conditions. This work contributes to the facile preparation of highly active and durable catalysts with improved catalytic performance mainly due to the predominance of nickel.Article HighlightsMnO2 and Ni-doped MnO2 nanowires were synthesized via a facile co-perception approach.Nickel doping in MnO2 induces the formation of wire-like nanostructures.Nickel doping enhances the electrochemical activity and thermal stability of MnO2 nanoflowers.The addition of nickel into MnO2 promoted the catalytic activity for oxygen reduction reaction.A higher catalytic activity was achieved in 0.125 M Ni-MnO2 nanowires.Graphic abstract

Design of core–shell structure NC@MoS2 hierarchical nanotubes as high-performance electromagnetic wave absorber

Using MnO2 nanowires as a template and coating with polydopamine, the MoS2 nanosheets are uniformly grown on the surface and the core–shell structure MnO2@NC@MoS2 nanowires are obtained after annealing. By etching and removing the MnO2 nanowires template with acid solution, NC@MoS2 wave absorber with tubular hollow structure is obtained. The design of the core–shell structure, the growth of MoS2 nanosheets, the existence of heterogeneous interfaces and the construction of tubular hollow structures effectively enhance the microwave absorption performance of NC@MoS2. The minimum reflection loss (RLmin) is reduced and the Effective absorption bandwidth (EAB) is broadened. Finally, the NC@MoS2 nanotube absorber has a RLmin of −52.56 dB, and the EAB is 6.0 GHz. As an efficient lightweight microwave absorber, NC@MoS2 has potential value in the synthesis and application of new composite microwave absorbing materials.

Direct Visualization of Atomic-Scale Heterogeneous Structure Dynamics in MnO2 Nanowires.

Manganese oxides are attracting great interest owing to their rich polymorphism and multiple valent states, which give rise to a wide range of applications in catalysis, capacitors, ion batteries, and so forth. Most of their functionalities are connected to transitions among the various polymorphisms and Mn valences. However, their atomic-scale dynamics is still a great challenge. Herein, we discovered a strong heterogeneity in the crystalline structure and defects, as well as in the Mn valence state. The transitions are studied by in situ transmission electron microscopy (TEM), and they involve a complex ordering of [MnO6] octahedra as the basic building tunnels. MnO2 nanowires synthesized using solution-based hydrothermal methods usually exhibit a large number of multiple polymorphism impurities with different tunnel sizes. Upon heating, MnO2 nanowires undergo a series of stoichiometric polymorphism changes, followed by oxygen release toward an oxygen-deficient spinel and rock-salt phase. The impurity polymorphism exhibits an abnormally high stability with interesting small-large-small tunnel size transition, which is attributed to a preferential stabilizer (K+) concentration, as well as a strong competition of kinetics and thermodynamics. Our results unveil the complicated intergrowth of polymorphism impurities in MnO2, which provide insights into the heterogeneous kinetics, thermodynamics, and transport properties of the tunnel-based building blocks.

Atomically Dispersed Manganese Lewis Acid Sites Catalyze Electrohydrogenation of Nitrogen to Ammonia

Atomically Dispersed Manganese Lewis Acid Sites Catalyze Electrohydrogenation of Nitrogen to Ammonia

α-MnO2 Nanowires and Amino-Modified Reduced Graphene Oxide Hybrid Films for Constructing the Flexible High-Performance Symmetrical Supercapacitors

Graphene or its derivates are used as an electrode material for the fabrication of supercapacitors (SCs). However, graphene or its composites readily agglomerate or stack in water, which seriously imparts SC energy efficiency. Presently, we used a new composite using [Formula: see text]-MnO2 nanowires and nitrogen-doped reduced graphene oxide ([Formula: see text]-MnO2/NRGO) for the fabrication of electrodes required in symmetric SCs. Hydrothermally synthesized [Formula: see text]-MnO2 nanowires have a smooth surface, good dispersion, and a high length-to-width ratio. The formation of stable and densely networked structures and the synergy between NRGO and [Formula: see text]-MnO2 nanowires enable the [Formula: see text]-MnO2/NRGO film electrode to show a large area-specific capacitance (386.8[Formula: see text]mF[Formula: see text]cm[Formula: see text]) at 1[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] current density; the capacity retention is 62.4% when the current density increases from 1[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] to 10[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text]. The flexible and symmetrical [Formula: see text]-MnO2/NRGO SC was assembled using [Formula: see text]-MnO2/NRGO film electrodes in 1 M Na2SO4 electrolyte with a cellulose paper separator, has good capacitance retention (94%), excellent Coulombic efficiency (99%) after 3000 cycles, and high energy density (28.22[Formula: see text][Formula: see text]Wh[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text]) at 0.8[Formula: see text]mW[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] power density. The [Formula: see text]-MnO2 nanowires/NRGO hybrid film flexible and symmetrical SCs are characterized by high energy storage, good cycle life and Columbic efficiency, which offer promising applications in the portable and wearable electronics industry.

Base-free oxidation of 5-hydroxymethylfurfural to 2, 5-furan dicarboxylic acid over nitrogen-containing polymers supported Cu-doped MnO2 nanowires

Nitrogen-containing polymer-supported Cu-doped MnO2 (Cu-MnO2@PDVTA) nanowires were prepared and their catalytic performances were evaluated via oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). The Cu-MnO2@PDVTA catalysts were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, N2 physical adsorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. Both the Cu2+ and MnO2 nanoparticles were found to synergistically promote HMF oxidation to FDCA via 2,5-furandicarbaldehyde and 5-formyl-2-furancarboxylic acid intermediates. The Cu-MnO2@PDVTA-3 catalyst demonstrated the highest catalytic activity, providing FDCA with an excellent yield of 96.8% after 12 h at 80 °C. The time course of HMF oxidation revealed that oxidation of the hydroxyl group in HMF was easier than that of the aldehyde group. Cu-MnO2@PDVTA-3 could act as a reusable heterogeneous catalyst for HMF oxidation.

Effective alkaline water electrolysis on nwMnO2-nsNi(OH)2 composite electrode via lattice oxygen participant adsorbate evolving mechanism

To improve and maintain the oxygen evolution reaction (OER) performance of MnO2 in water electrolysis for a long time, this study attempts to utilize Ni(OH)2 nanosheets (ns), which have excellent electrochemical properties. Nanocomposites of MnO₂ and Ni(OH)2 were directly grown on a carbon paper (CP) electrode using hydrothermal synthesis. The MnO2 nanowires (nw) appeared to be wrapped by the Ni(OH)2 nanosheets in the MnO2-Ni(OH)2 composites. The MnO2-Ni(OH)2 composite electrode exhibited better OER performance than the nwMnO2@CP or nsNi(OH)2@CP electrodes. In particular, in a 1.0 M KOH alkaline electrolyte, the 1.0 nwMnO2-1.0 nsNi(OH)2@CP electrode showed the highest OER performance with a cell potential of 1.64 V and Tafel slope of 68 mV dec−1 at a 10 mA cm−2 of current density (η = 0.41 V). The X-ray photoelectron spectroscopy of nwMnO2-nsNi(OH)2@CP before and after the OER revealed the formation of more oxygen vacancies, which served as OH-adsorption sites, leading to higher OER activity. The stability of the 1.0 nwMnO2-1.0 nsNi(OH)2@CP electrode was demonstrated through 300 h-OER long-term tests, which yielded a high Faradaic efficiency of 96.2%. The lattice oxygen transfer plays a significant role in enhancing the intrinsic activity of catalysts during OER. The synergy between nwMnO2 and nsNi(OH)2 accompanies a lattice oxygen participant adsorbate evolving mechanism.

Promoting the Performance of Li-CO2 Batteries via Constructing Three-Dimensional Interconnected K+ Doped MnO2 Nanowires Networks.

Nowadays, Li–CO2 batteries have attracted enormous interests due to their high energy density for integrated energy storage and conversion devices, superiorities of capturing and converting CO2. Nevertheless, the actual application of Li–CO2 batteries is hindered attributed to excessive overpotential and poor lifespan. In the past decades, catalysts have been employed in the Li–CO2 batteries and been demonstrated to reduce the decomposition potential of the as-formed Li2CO3 during charge process with high efficiency. However, as a representative of promising catalysts, the high costs of noble metals limit the further development, which gives rise to the exploration of catalysts with high efficiency and low cost. In this work, we prepared a K+ doped MnO2 nanowires networks with three-dimensional interconnections (3D KMO NWs) catalyst through a simple hydrothermal method. The interconnected 3D nanowires network catalysts could accelerate the Li ions diffusion, CO2 transfer and the decomposition of discharge products Li2CO3. It is found that high content of K+ doping can promote the diffusion of ions, electrons and CO2 in the MnO2 air cathode, and promote the octahedral effect of MnO6, stabilize the structure of MnO2 hosts, and improve the catalytic activity of CO2. Therefore, it shows a high total discharge capacity of 9,043 mAh g−1, a low overpotential of 1.25 V, and a longer cycle performance.

Head space solid phase microextraction of 15 pesticides in water samples using MnO2 nanowires decorate on graphenized pencil lead fiber

ABSTRACT Nanowires of porous MnO2 were directionally decorated on graphenized pencil lead and used as a fiber coating for selectively analysis of the 15 pesticides by headspace solid-phase microextraction (HS-SPME) method. The as-synthesized materials were characterized by scanning microscopy, thermal gravimetric analysis, and energy-dispersive X-ray spectrometer (EDX). According to the results, this coating indicated considerable potential due to extracting simultaneously traces amounts of 15 pesticides in aqueous matrices. The essential parameters such as extraction time, extraction temperature, agitation speed, and ionic strength of sample that mainly affect the adsorption process were optimized and in optimum values, the repeatabilities for one fiber were between 3.5% and 6.3% for the test compounds were achieved. The detection limits for the studied compounds were between 0.029 and 0.418 µgL−1. It is a simple, quick, and cheap approach.

Utilization of high‑sulfur-containing petroleum coke for making sulfur-doped porous carbon composite material and its application in supercapacitors

As a by-product generated in a large amount in petroleum refining, high‑sulfur petroleum coke has very limited applications except being used as a fuel for combustion. To extend its applications, various utilization pathways have been seeking for many years. In this work, an attempt was made for the preparation of a sulfur-doped hierarchical porous carbon (HPC) directly from the high‑sulfur petroleum coke without using the external sulfur. A HPC with a surface area of 3318 m2 g−1 was successfully prepared by the one-step method, which has excellent electrochemical performance with a specific capacitance of 327 F g−1 at the current density of 1 A g−1. Moreover, the HPC was further modified with MnO2 nanowires to form a porous composite material, which was used for making high-performance supercapacitors. Amazingly, a higher specific capacitance of 480 F g−1 was achieved at the current density of 1 A g−1. The asymmetric supercapacitor that was assembled using the HPC/MnO2 and HPC as the positive and negative electrode respectively in 1 M Na2SO4 solution had achieved a maximum energy density of 49.7 Wh kg−1 at the power density of 450 W kg−1, which is better than most of the data reported in literature. This study suggested that the high‑sulfur petroleum coke could be a suitable source for making sulfur doped porous carbon composite materials, which are very promising for applications in supercapacitors.

Dual-Functional Template-Induced In Situ Polymerization Process Enables the Hierarchical Carbonaceous Nanotubes with Simultaneous Sn Cluster Incorporation and Nitrogen-Doping for Superior Potassium-Ion Storage.

Potassium ion-based energy storage devices have received extensive attention for grid-level applications due to their abundant natural resources and low cost. However, the large ionic radius of K+ leads to inferior capacities and cyclic stability, which hinders their practical application. Herein, hierarchical carbonaceous nanotubes with simultaneous ultrasmall Sn cluster incorporation and nitrogen doping (denoted as u-Sn@NCNTs) are fabricated using MnO2 nanowires as a dual-functional template (in situ polymerization and shape-directing agents) and subsequent carbonization treatment. The u-Sn@NCNTs exhibit a superior K+ storage capability with a high reversible capacity (220.1 mA h g-1 at 0.1 A g-1) and long cycling stability (149.9 mA h g-1 at 1 A g-1 after 4000 cycles). Besides, the u-Sn@NCNTs exhibit superior cycling stability up to 10000 cycles at 5 A g-1 for Na+ storage. The potassium storage mechanism and kinetics are investigated based on ex situ X-ray photoelectron spectroscopy, in situ Raman spectrum, and galvanostatic intermittent titration technique. More importantly, u-Sn@NCNTs can be used as the anode for potassium ion hybrid capacitors, achieving a superior energy density of 181.4 W h kg-1 at a power density of 185 W kg-1 with excellent cycling capability. This work could push forward the development and application of carbonaceous-based anode materials for next-generation high-performance rechargeable batteries.

Novel fabrication method of hierarchical planar micro-supercapacitor via laser-induced localized growth of manganese dioxide nanowire arrays

Micro-supercapacitors are enormously needed, owing to increasing energy demands in miniaturizing mobile electronic devices. Manganese dioxide (MnO2) is one of the most popular micro-supercapacitor electrode materials that can be applied with various fabrication methods. However, in case of the conventional fabrication of MnO2-based micro-supercapacitor, fabrication methods require complex multiple steps or sophisticated patterning techniques for MnO2 selective micro-patterning. Thus, it is difficult to improve space utilization of micro-supercapacitor and apply them to further another application. In this study, we introduce a novel fabrication method of hierarchical planar micro-supercapacitor using MnO2 nanowire (NW) arrays. Using laser-induced hydrothermal growth (LIHG) process, MnO2 NW arrays are vertically grown on selective area in the desired location under ambient conditions. For the stable growth of vertically aligned MnO2 NW array using LIHG process, various laser parameters, including irradiation time and power, are adjusted. Afterward, the vertically grown MnO2 NW arrays are applied to fabricate hierarchical planar micro-supercapacitor, showing high areal capacitance of 227 mF cm−2 (at 1 mA cm−2) in terms of footprint area on tiny 2D plane. Thus, the proposed approach can be considered as a new fabrication method for capacitance enhancement of planar micro-supercapacitor.

Cobalt-Doped Manganese Dioxide Hierarchical Nanostructures for Enhancing Pseudocapacitive Properties.

Herein, overall improvement in the electrochemical performance of manganese dioxide is achieved through fine-tuning the microstructure of partially Co-doped manganese dioxide nanomaterial using facile hydrothermal method with precise control of preparative parameters. The structural investigation exhibits formation of a multiphase compound accompanied by controlled reflections of α-MnO2 as well as γ-MnO2 crystalline phases. The morphological examination manifests the presence of MnO2 nanowires having a width of 70–80 nm and a length of several microns. The Co-doped manganese dioxide electrode displayed a particular capacitive behavior along with a rising order of capacitance concerning with increased cobalt ion concentration suitable for certain limits. The value of specific capacitance achieved by a 5% Co-doped manganese dioxide sample was 1050 F g–1 at 0.5 A g–1, which was nearly threefold greater than that achieved by a bare manganese dioxide electrode. Furthermore, Co-doped manganese dioxide nanocomposite electrode exhibits exceptional capacitance retention (92.7%) till 10,000 cycles. It shows the good cyclability as well as stability of the material. Furthermore, we have demonstrated the solid-state supercapacitor with good energy and power density.