Rational design of nickel cobalt sulfide/oxide core-shell nanocolumn arrays for high-performance flexible all-solid-state asymmetric supercapacitors

The development of wearable electronics has created a surge of interest in designing flexible energy storage device with high energy density and long lifespan. In this work, we have successfully fabricated a flexible asymmetric supercapacitor (ASC) based on the NiCo₂S₄@NiCo₂O₄ nanocolumn arrays (NCAs). The nickel cobalt sulfide/oxide core-shell nanostructures were rationally synthesized through a facile stepwise approach. The NiCo₂S₄@NiCo₂O₄ NCAs based electrode delivered a high specific capacitance of 2258.9 F g⁻¹ at a current density of 0.5 A g⁻¹. The as-assembled flexible ASC device exhibited a high energy density of 44.06 Wh kg⁻¹, a high power density of 6.4 kW kg⁻¹, and excellent cycling stability by retaining 92.5% after 6000 cycles. Excitingly, the electrochemical property of the ASC device could be maintained under severe bending, indicating superior flexibility and mechanical stability. The NiCo₂S₄@NiCo₂O₄ core-shell NCAs possess enormous potential for future wearable electronic applications.     

A facile synthesis of ZnMn2O4/Mn2O3 composite nanostructures for supercapacitor applications

This article reports the preparation of new ZnMn₂O₄/Mn₂O₃ composites by ultrasonication and microwave irradiation assisted hydrothermal method. The composite formation (ZnMn₂O₄/Mn₂O₃) is confirmed by powder X-ray diffraction, X-ray photoelectron spectroscopy and micro-Raman spectroscopy. The four ‘petals’ flower and six ‘petals’ flower-shaped morphology of composite material are confirmed through scanning electron microscopic analysis. The synthesis method directly influences the morphology of the composites. Further, nanosized composite formation is confirmed through transmission electron microscopic analysis. The prepared composite materials' electrochemical properties are studied using a three-electrode system and it shows a pseudocapacitance nature. The high specific capacitance of 380 F/g @ 0.5 A/g is found for the composite material in galvanostatic charge-discharge studies. The prepared ZnMn₂O₄/Mn₂O₃ composite shows an excellent cycling stability of 92% of the initial specific capacitance at current density of 3 A/g after 2000 cycles. Electrochemical studies of the composite reveal that the ZnMn₂O₄/Mn₂O₃ composite can be used for supercapacitor applications.     

Manganese dioxide nanosheets decorated on MXene (Ti3C2Tx) with enhanced performance for asymmetric supercapacitors

The incorporation of nanosized pseudocapacitive materials and structure design are general strategies to enhance the electrochemical performance of MXene-based materials. Herein, the decoration of manganese dioxide (MnO₂) nanosheets on MXene (Ti₃C₂T_x) surfaces was prepared by a facile liquid phase coprecipitation method. Ti₃C₂T_x is initially modified by polydopamine (PDA) coating to ensure the homogeneous distribution of MnO₂ nanosheets and tight and close connections between MnO₂ and the Ti₃C₂T_x backbone. Due to the obtained three-dimensional (3D) nanostructure, facilitating electron transport within the electrode and promoting electrolyte ion accessibility, the δ-MnO₂@Ti₃C₂T_x-0.06 electrode yields superior electrochemical performances, such as a rather large areal capacity of 1233.1 mF cm^?2 and high specific capacitance of 337.6 F g^?1 at 2 mV s^?1, as well as high cyclic stability for 10000 cycles. Furthermore, δ-MnO₂@Ti₃C₂T_x-0.06 composites are employed as positive electrodes, and activated carbon (AC) materials act as negative electrodes with an aqueous electrolyte of 1 M Na₂SO₄ to assemble asymmetric supercapacitors. The prototype device is reversible at cell voltages from 0 to 1.8 V, and manifests a maximum energy density of 31.4 Wh kg^?1 and a maximum power density of 2700 W kg^?1. These encouraging results show enormous possibilities for energy storage applications.     

Coaxial carbon nanofibers/MnO2 nanocomposites as freestanding electrodes for high-performance electrochemical capacitors

Carbon nanofibers (CNFs)/MnO₂ nanocomposites were prepared as freestanding electrodes using in situ redox deposition and electrospinning. The electrospun CNFs substrates with porosity and interconnectivity enabled the uniform incorporation of birnessite-type MnO₂ deposits on each fiber, thus showing unique and conformal coaxial nanostructure. CNFs not only provided considerable specific surface area for high mass loading of MnO₂ but also offered reliable electrical conductivity to ensure the full utilization of MnO₂ coatings. The effect of MnO₂ loading on the electrochemical performances was investigated by cyclic voltammetry (CV), impedance measurements and Galvonostatic charging/discharging technique. The results showed that an ultrathin MnO₂ deposits were indispensable to achieve better electrochemical performance. The maximum specific capacitance (based on pristine MnO₂) attained to 557 F/g at a current density of 1 A/g in 0.1 M Na₂SO₄ electrolyte when the mass loading reached 0.33 mg/cm². This freestanding electrode also exhibited good rate capability (power density of 13.5 kW/kg and energy density of 20.9 Wh/kg at 30 A/g) and long-term cycling stability (retaining 94% of its initial capacitance after 1500 cycles). These characteristics suggested that such freestanding CNFs/MnO₂ nanocomposites are promising for high-performance supercapacitors.     

Synthesis of a MnO2–graphene foam hybrid with controlled MnO2 particle shape and its use as a supercapacitor electrode

A simple approach was developed to synthesize the three-dimensional (3D) hybrid of manganese dioxide (MnO₂) and graphene foam. The morphology of the MnO₂ nanostructures can be readily controlled by the solution acidity. Furthermore, we demonstrate that, serving as a free-standing supercapacitor electrode, this novel three-dimensional hybrid gives a remarkable specific capacitance (560 F/g at the current density of 0.2 A/g) and excellent cycling stability.     

Self-standing manganese dioxide/graphene carbon nanotubes film electrode for symmetric supercapacitor with high energy density and superior long cycling stability

The low capacitance utilization and capacitance fading of manganese dioxide (MnO₂) is mainly due to poor electro-conductivity and irreversible phase transform. This work proposes a new method of designing hierarchical and binder-free electrode based on MnO₂ material for stable supercapacitor with high specific capacitance. Herein, we fabricated the self-standing electrode of MnO₂ on nitrogen-doped graphene and single wall carbon nanotubes (SWCNTs) self-standing film (NGCF) by electrochemical deposition. As a result, as-prepared MnO₂/NGCF cathode showed excellent electrochemical performance of 489.7 F g^-1 at 1 A g^-1. Assembled symmetric aqueous supercapacitor (SC) manifests high voltage of 2.4 V and presents excellent high energy density of 106.7 Wh kg^-1 at 1200 W kg^-1 and outstanding long-life stability without no decay after 10 000 charge-discharge circuits. This work proposes a new view of designing hierarchical and binder-free electrode with high energy density and long cycling stability based on MnO₂ material for stable symmetric supercapacitor.     

Effect of Ge on microstructure and mechanical properties of Ti3SiC2/Al2O3 composites

Owing to the good physicochemical compatibility and complementary mechanical properties of Ti₃SiC₂ and Al₂O₃, Ti₃SiC₂/Al₂O₃ composites are considered as ideal structural materials. However, TiC and TiSi₂ typically coexist during the synthesis of Ti₃SiC₂/Al₂O₃ composites through an in-situ reaction, which adversely affects the mechanical properties of the resulting composites. In this study, Ti₃SiC₂/Al₂O₃ composites were prepared via in-situ hot pressing sintering at 1450 °C. Ge, which was used as a sintering aid, improved the purity and mechanical properties of the Ti₃SiC₂/Al₂O₃ composites. This is because Ge replaced some of the Si atoms to compensate the evaporation loss of Si to form Ti₃(Si_1-xGe_x)C₂, which showed a crystal structure similar to that of Ti₃SiC₂. Furthermore, the molten Ge accelerated the diffusion reaction of the raw materials, increasing the overall density of the Ti₃SiC₂/Al₂O₃ composites. The optimum Ge amount for improving the mechanical properties of the composites was found to be 0.3 mol. The flexural strength, fracture toughness, and microhardness of the composite with the optimum Ge amount were 640.2 MPa, 6.57 MPa m^1/2, and 16.21 GPa, respectively. The formation of Ti₃(Si_1-xGe_x)C₂ was confirmed by carrying out X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy analyses. A model crystal structure of Ti₃(Si_1-xGe_x)C₂ doped with 0.3 mol Ge was established by calculating the solid solubility of Ge.     

Encapsulation of manganese oxides nanocrystals in electrospun carbon nanofibers as free-standing electrode for supercapacitors

Flexible composites with manganese oxides (MnO_x) nanocrystals encapsulated in electropun carbon nanofibers were successfully fabricated via a simple and practical combination of electrospinning and carbonization process. The as-formed MnO_x/carbon nanofibers composites have a rough surface with MnO_x nanoparticles well embedded in the carbon nanofibers backbones. When used as electrodes for supercapacitor, the resulting MnO_x/carbon nanofiber composites exhibit good electrochemical performance with a specific capacitance of 174.8 F g⁻¹ at 2 mV s⁻¹ in 0.5 M Na₂SO₄ electrolyte, a good rate capability at high current density and long-term cycling stability. It is expected that such freestanding composites could be promising electrodes for high-performance supercapacitors.     

Cooperative effect of hierarchical carbon nanotube arrays as facilitated transport channels for high-performance wire-based supercapacitors

It is demonstrated that hierarchical nanostructures can greatly enhance the performances of a wire-based supercapacitor (WS), meanwhile can also increase the WS's volume and further hamper the improvement of the WS's capacitance per unit volume. Here a type of three dimensional hierarchical MnO₂@carbon nanotube array (CNTA) composites has been designed on stainless steel wires (SSWs) and the cooperative effects of various parameters (such as MnO₂ masses, CNTA lengths and wire lengths) on the electrochemical performances of the wire electrodes are systematically investigated. Results show that the specific capacitance of the electrodes can be optimized by MnO₂ masses and array lengths, while independent to wire lengths. Moreover, the optimized MnO₂@CNTA/SSW electrodes can exhibit high capacitance (9.1 mF cm⁻¹ at 5 mV s⁻¹), good rate-capability (64.46% at 3 A cm⁻³), and high cycle retention (84.8% after 1000 cycles). Furthermore, the assembled all-solid state flat symmetrical WSs show desirable capacitive behaviors (∼0.78 mW h cm⁻³) and good flexibility.     

Integration of MnO2 and ZIF-Derived nanoporous carbon on nickel foam as an electrode for high-performance supercapacitors

MnO₂ has the highest potential as a supercapacitor electrode; however, its disadvantage in electronic conductivity hinders its widespread use. This study reports the excellent electrochemical performance of MnMC/NF (MnO₂ and ZIF-derived nanoporous carbon on nickel foam) composites. MnMC/NF composites are produced when leaf-like Co-ZIF is annealed on nickel foam, followed by potassium permanganate treatment. When the annealing temperature reaches 700 °C, the maximum specific capacitance of 531 F/g is achieved at 1 A/g (456 F/g at 20 A/g) with a rate capability of 85.5%. MnMC/NF700 has a long cyclic stability, and the capacitance retention was 82% after 5000 cycles. The energy density of an assembled device using MnMC/NF700 composite as positive electrodes can reach 38.8 Wh/kg. This is due to the combined effect of nickel substrate's 3D porous structure and the excellent electronic conductivity of ZIF-derived nanoporous carbon. The unique configuration of MnMC/NF composites may provide a referable design for energy storage systems, including materials that have the highest potential for use as supercapacitor electrodes.     

One-step electrosynthesis of MnO2/rGO nanocomposite and its enhanced electrochemical performance

We present a facile one-step electrochemical approach to generate MnO₂/rGO nanocomposite from a mixture of Mn₃O₄ and graphene oxide (GO). The electrochemical conversion of Mn₃O₄ into MnO₂ through potential cycling is expedited in the presence of GO while the GO is reduced into reduced graphene oxide (rGO). The MnO₂ nanoparticles are evenly distributed on the rGO nanosheets and act as the spacer to prevent rGO nanosheets from restacking. This unique structure provides high electroactive surface area (1173?m² g^?1) that improves ions diffusion within the MnO₂/rGO structure. As a result, the MnO₂/rGO nanocomposite exhibits high specific capacitance of 473?F?g^?1 at 0.25?A?g^?1, which is remarkably higher (3 times) than the Mn₃O₄/GO prior conversion. In addition, the electrosynthesized nanocomposite shows higher conductivity and excellent potential cycling stability of 95% at 2000 cycles.     

One-step hydrothermal synthesis of hybrid core-shell Co3O4@SnO2–SnO for supercapacitor electrodes

We successfully synthesized a novel core-shell hybrid metal oxide via a simple one-step hydrothermal method without annealing. This composite of Co₃O₄ particles covered with SnO₂–SnO (Co₃O₄@SnO₂–SnO) predicted better performance compared to pure Co₃O₄, which strongly depends on the synthetic temperature. The Co₃O₄@SnO₂–SnO prepared at a temperature of 250 °C (labeled Co₃O₄@SnO₂–SnO-250) exhibited an outstanding specific capacitance of 325 F g⁻¹ under the current density of 1 A g⁻¹, which was much higher than those of Co₃O₄ (12.6 F g⁻¹) and other composites. Additionally, the sample also exhibited good cycle stability performance with a retention rate of 100% after 5000 cycles at a current density of 5 A g⁻¹. Through X-ray photoelectron spectroscopy analysis, the presumed mechanism was that Sn-O_x decreases the surface electron densities of Co₃O₄, which is beneficial to OH⁻ adsorption and specific capacitance improvement, and the synthetic temperature had a strong impact on the microstructure and thus on the surface electron densities. The most.obvious finding to emerge from this study is that the specific capacitance can be improved through adjusting the surface electron densities of transition metal oxides.     

Bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide as electrochromic asymmetric supercapacitor

A bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide (MnO₂/V₂O₅/rGO) was developed for asymmetric electrochromic supercapacitor (EC-SC) application. The elemental mapping revealed uniformly distributed MnO₂, V₂O₅ and rGO, depicting homogenous synthesis of the hybrid composite. The phase composition, vibration modes and valance state of the ternary composite were analyzed via X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis, respectively. Interestingly, the as-prepared MnO₂/V₂O₅/rGO composite disclosed tremendous C_sp of 1403.5 F/g, which was higher compared to MnO₂/V₂O₅ (801.1 F/g), V₂O₅ (613.1 F/g), MnO₂ (126.7 F/g) and rGO (60.7 F/g). MnO₂/V₂O₅/rGO that appeared in dark green switched its visual color to orange at the charged state, confirming the electrochromic property. The bifunctional manganese oxide/vanadium oxide/reduced graphene oxide//copper-based metal-organic framework/reduced graphene oxide (MnO₂/V₂O₅/rGO//MrGO) asymmetrical EC-SC device revealed outstanding cycling stability (90.3% charge retention over 5000 cycles), tremendous specific capacitance (652.7 F/g) and maximum specific energy (60.4 Wh/kg). MnO₂/V₂O₅/rGO//MrGO asymmetrical EC-SC device demonstrated reversible color changes from dark green to orange at the discharged and charged states, respectively. The significantly great electrochromic and supercapacitive performance revealed that MnO₂/V₂O₅/rGO//MrGO is an outstanding electroactive candidate for the next generation of electrochromic supercapacitors.     

Microstructure and strengthening behavior in high content SiC nanowires reinforced SiC composites

In this study, the high-content SiC_nw reinforced SiC ceramic matrix composites (SiC_nw/SiC CMC) were successfully fabricated by hot pressing β-SiC and sintering additive (Al₂O₃-Y₂O₃) with boron nitride interphase modification SiC_nw. The effects of sintering additive content and mass fraction (5–25 wt%) of SiC_nw on the density, microstructure, and mechanical properties of the composites were investigated. The results showed that with the increase of sintering additives from 10 wt% to 12 wt%, the relative density of the SiC_nw/SiC CMC increased from 97.3% to 98.9%, attributed to the generated Y₃Al₅O₁₂ (YAG) liquid phase from the Al₂O₃-Y₂O₃ that promotes the rearrangement and migration of SiC grains. The comprehensive performance of the obtained composite with 15 wt% SiC_nw possessed the optimal flexural strength and fracture toughness of 524 ± 30.24 MPa and 12.39 ± 0.49 MPa·m^1/2, respectively. Besides, the fracture mode of the composites with 25 wt% SiC_nw content revealed a pseudo-plastic fracture behavior. It concludes that the 25 wt% SiC_nw/SiC CMC was toughened by the fiber pull-outs, debonding, bridging, and crack deflection that can consume plenty of fracture energy. The strategy of SiC nanowires worked as a main bearing phase for the fabrication of SiC/SiC CMC providing critical information for understanding the mechanical behavior of high toughness and high strength SiC nanoceramic matrix composites.     

ZnCo2O4/CNT composite for efficient supercapacitor electrodes

Due to their combination of enhanced electrical conductivity and high-performance electron and ion transport channels, binary metal oxides with well-morphological optimized electrode materials have been attracted the greatest research attention for high-performance supercapacitor applications. An easy co-precipitation method is used to synthesize ZnCo₂O₄ nanoparticles using NaOH and Urea as precipitation agents. To facilitate electrical conductivity, suitable carbon material such as carbon nanotube (CNT) has been added to make a composite material. The three-electrode system was preferred for estimating specific capacitance of prepared material and optimally efficient ZnCo₂O₄/CNT electrode delivered a moderate 888 F/g capacitance at 1 A/g in 3 M KOH and after 5000 charge discharge cycles 94.72% of cycling stability retained at 5 A/g. This paper presents a little price and simple procedure for preparation of ZnCo₂O₄/CNT electrode that promotes creative sprit for energy storage applications.     

Facile synthesis of three dimensional flower-like Co3O4@MnO2 core-shell microspheres as high-performance electrode materials for supercapacitors

In this work, we reported the synthesis of three dimensional flower-like Co₃O₄@MnO₂ core-shell microspheres by a controllable two-step reaction. Flower-like Co₃O₄ microspheres cores were firstly built from the self-assembly of Co₃O₄ nanosheets, on which MnO₂ nanosheets shells were subsequently grown through the hydrothermal decomposition of KMnO₄. The MnO₂ nanosheets shells were found to increase the electrochemical active sites and allow faster redox reaction kinetics. Based on these advantages, when used as an electrode for supercapacitors, the prepared flower-like Co₃O₄@MnO₂ core-shell composite electrode demonstrated a significantly enhanced specific capacitance (671 F g⁻¹ at 1 A g⁻¹) as well as improved rate capability (84% retention at 10 A g⁻¹) compared with the pristine flower-like Co₃O₄ electrode. Moreover, the optimized asymmetric supercapacitor device based on the flower-like Co₃O₄@MnO₂//active carbon exhibited a high energy density of 34.1 W h kg⁻¹ at a power density of 750 W kg⁻¹, meaning its great potential application for energy storage devices.     

Polymer-derived Co2Si@SiC/C/SiOC/SiO2/Co3O4 nanoparticles: Microstructural evolution and enhanced EM absorbing properties

In this work, porous core-shell structured Co₂Si@SiC/C/SiOC/SiO₂/Co₃O₄ nanoparticles were fabricated by a polymer-derived ceramic approach. The in situ formation of mesopores on the shell, microstructural, and phase evolution of resulting nanoparticles were investigated in detail. The obtained nanoparticles-paraffin composites possess a very low minimum reflection coefficient (RC_min) −60.9 dB, broad effective absorption bandwidth 3.50 GHz in the X-band and 15.5 GHz in the whole frequency range (from 2.5 to 18 GHz). The results indicate outstanding electromagnetic wave (EMW) absorbing performance among all the reported cobalt-based nanomaterials, due to the reasons as follows: (a) The unique core-shell structure as well as complex phase composition of SiC/C/SiOC/SiO₂/Co₃O₄ in the shell, result in a large number of heterogeneous interfaces in the nanoparticles; (b) Nanoparticles have both dielectric and magnetic loss; (c) Mesopores in the shell prolong the propagation path of EMW, thereby increasing the absorption/reflection ratio of EMWs. Thanks to the material structure design, the resulting core-shell structured cobalt-containing ceramic nanoparticles have great potential for thin and high-performance EMW absorbing materials applied in harsh environment.     

Hydrothermal synthesis and characterization studies of α-Fe2O3/MnO2 nanocomposites for energy storage supercapacitor application

In this present study, semiconductor magnetic α-Fe₂O₃/MnO₂ nanocomposites (NCs) were prepared by a facile hydrothermal (HT) method. The crystallographic structure, morphology, chemical configuration and magnetic features were analysed by X-ray powder diffraction (XRD), high resolution scanning electron microscope (HR-SEM), energy dispersive X-ray analysis (EDX), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) analyses. The as-prepared NCs were used as an electrode in energy storing supercapacitor was systematically examined. The electrochemical deeds of α-Fe₂O₃/MnO₂ NCs was analysed by cyclic voltammetry (C–V) and galvanostatic charge–discharge (GCD) tests. The CV analysis of the NCs electrode showed a distinctive pseudocapacitive behaviour in 1 M KOH solution. The NCs electrode reveals enhanced specific capacitance compared to plain α-Fe₂O₃ and MnO₂ nanoparticles (NPs) and generates high specific capacitance of 216.35 Fg⁻¹. Pseudocapacitor obtains of energy density 135.42 Wh kg⁻¹ at power density of 6.399 kW kg⁻¹, indicating the as-prepared α-Fe₂O₃/MnO₂ NCs shows noteworthy high-energy, specific capacitance, power densities and long-standing cyclic stability with 89.2% of preliminary capacitance reserved at 1A g⁻¹ after 10000 cycles in judgement with the pure α-Fe₂O₃ and MnO₂ NPs electrode. The α-Fe₂O₃/MnO₂ NCs electrode having noteworthy electrochemical characteristics performance renders promising applications in energy storing systems.     

Facile synthesis and characterization of conducting polymer-metal oxide based core-shell PANI-Pr2O–NiO–Co3O4 nanocomposite: As electrode material for supercapacitor

Metal oxide nanoparticles and their composites with conducting polymers, specifically Polyaniline (PANI) were utilized for fabricating nanoscale supercapacitor (SC) electrode materials. In the present study, we have synthesized pristine Pr₂O₃, NiO, Co₃O₄ nanoparticles, binary PANI-Pr₂O₃, PANI-NiO, PANI-Co₃O₄, ternary Pr₂O₃–NiO–Co₃O₄, and quaternary PANI-Pr₂O₃–NiO–Co₃O₄ spherical core-shell nanocomposite using co-precipitation and ultra-sonication methods. The grown samples were characterized with different analytical techniques. The XRD pattern revealed that the as-synthesized products were crystalline with Pr₂O₃ hexagonal phase, NiO cubic phase, and Co₃O₄ cubic phase in pure and nanocomposites. The Williamson-Hall, Scherrer, and size-strain plot methods were employed to study the crystalline development and contribution of micro-strain. FTIR pattern exhibited the metal-oxygen and PANI bond vibrations. FE-SEM images shown the spherical core-shell shape morphology of quaternary nanocomposite. EDX evident the presence of praseodymium, cobalt, and nickel in synthesized samples. UV–vis spectroscopy confirmed the absorption in the visible region. The IV graphs showed a higher conductivity of quaternary nanocomposite. The cyclic voltammetry results revealed that the quaternary nanocomposite has a higher specific capacitance 500 Fg^-1 as compared to binary nanocomposites 134 F g^?1 (PANI-Pr₂O₃), 143 F g^?1 (PANI-Co₃O₄), 256 F g^?1 (PANI-NiO), and PANI (90.8 F g^?1) at a scan rate of 5 m Vs^?1. The GCD results also showed that the quaternary nanocomposite has a higher specific capacitance of 905 F g^?1 at current density 1 A g^?1 with maximum energy density and power density of 87.99 kWhkg^-1 and 2.6 k W kg^?1_, respectively. The EIS curve also confirmed that the quaternary nanocomposite has a lower polarization resistance (R_p) and solution resistance (R_s). The higher capacitance of quaternary nanocomposite can facilitate ion transfer, and the formation of its core-shell structure flourish to enhance surface-dependent electrochemical properties. Furthermore, this study gives a novel research idea to manufacture electrode materials for supercapacitors.     

Construction of spherical NiO@MnO2 with core-shell structure obtained by depositing MnO2 nanoparticles on NiO nanosheets for high-performance supercapacitor

The 3D spherical NiO@MnO₂ composites grown on Ni foam with core-shell structure were prepared by a hydrothermal process followed by a chemical bath deposition process, and then the mechanism improving the electrochemical performance of NiO by MnO₂ modification were investigated by the first-principles calculations for the first time. This core-shell structure promotes an efficient contact between electrolyte and active materials, and the distinct architecture can offer fast transfer channels of ion and electrons. The initial capacitances of NiO, NiO@MnO₂ (deposition time of MnO₂ is 20 min), NiO@MnO₂ (deposition time of MnO₂ is 30 min) and NiO@MnO₂ (deposition time of MnO₂ is 60 min) at 10 A g⁻¹ are 931.6, 1064.4, 1227.2 and 766.8 F g⁻¹, respectively. After 10000 cycles, the reversible capacitances attenuate to 352.8, 661.0, 1089.4 and 616.6 F g⁻¹, respectively. NiO@MnO₂ (deposition time of MnO₂ is 30 min) shows the most excellent reversible capacitance at each cycle and the highest retention rates after 10000 cycles among all samples. The first-principles calculation confirms that a strong interfacial interaction between NiO and MnO₂ can be generated, and then the atomic relaxations at the interface are rather small due to the well-matched interface and epitaxial bonding, resulting in a relatively small interfacial polarization of NiO@MnO₂ composites during cycling. The outstanding rate capability and cycle performance of NiO@MnO₂ (deposition time of MnO₂ is 30 min) electrode are attributed to the synergistic effect and particular 3 D architectures.