Hierarchical FeCo2S4@FeNi2S4 Core/Shell Nanostructures on Ni Foam for High-Performance Supercapacitors

The design of electrode materials with rational core/shell structures is promising for improving the electrochemical properties of supercapacitors. Hence, hierarchical FeCo₂S₄@FeNi₂S₄ core/shell nanostructures on Ni foam were fabricated by a simple hydrothermal method. Owing to their structure and synergistic effect, they deliver an excellent specific capacitance of 2393 F g⁻¹ at 1 A g⁻¹ and long cycle lifespan as positive electrode materials. An asymmetric supercapacitor device with FeCo₂S₄@FeNi₂S₄ as positive electrode and graphene as negative electrode exhibited a specific capacitance of 133.2 F g⁻¹ at 1 A g⁻¹ and a high energy density of 47.37 W h kg⁻¹ at a power density of 800 W kg⁻¹. Moreover, the device showed remarkable cycling stability with 87.0 % specific-capacitance retention after 5000 cycles at 2 A g⁻¹. These results demonstrate that the hierarchical FeCo₂S₄@FeNi₂S₄ core/shell structures have great potential in the field of electrochemical energy storage.     

Hollow 3D Frame Structure Modified with NiCo2S4 Nanosheets and Spinous Fe2O3 Nanowires as Electrode Materials for High-Performance All-Solid-State Asymmetric Supercapacitors

Supercapacitors have attracted tremendous research interest, since they are expected to achieve battery-level energy density, while having a long calendar life and short charging time. Herein, a novel asymmetric supercapacitor has been successfully assembled from NiCo₂S₄ nanosheets and spinous Fe₂O₃ nanowire modified hollow melamine foam decorated with polypyrrole as positive and negative electrodes, respectively. Owing to the well-designed nanostructure and suitable matching of electrode materials, the assembled asymmetric supercapacitor (ASC) exhibits an extended operation voltage window of 1.6 V with an energy density of 20.1 Wh kg⁻¹ at a power density of 159.4 kW kg⁻¹. Moreover, the ASC shows stable cycling stability, with 81.3 % retention after 4000 cycles and a low internal resistance of 1.03 Ω. Additionally, a 2.5 V light-emitting diode indicator can be lit up by three ASCs connected in series; this provides evidence of the practical application potential of the assembled energy-storage system. The excellent electrochemical performances should be credited to the significant enhancement of the specific surface area, charge transport, and mechanical stability resulting from the unique 3D morphology.     

Hierarchical Carbon Nanowire/Ni@MnO2 Nanocomposites for High-Performance Asymmetric Supercapacitors

A 3D hierarchical carbon cloth/nitrogen-doped carbon nanowires/Ni@MnO₂ (CC/N-CNWs/Ni@MnO₂) nanocomposite electrode was rationally designed and prepared by electrodeposition. The N-CNWs derived from polypyrrole (PPy) nanowires on the carbon cloth have an open framework structure, which greatly increases the contact area between the electrode and electrolyte and provides short diffusion paths. The incorporation of the Ni layer between the N-CNWs and MnO₂ is beneficial for significantly enhancing the electrical conductivity and boosting fast charge transfer as well as improving the charge-collection capacity. Thus, the as-prepared 3D hierarchical CC/N-CNWs/Ni@MnO₂ electrode exhibits a higher specific capacitance of 571.4 F g⁻¹ compared with those of CC/N-CNWs@MnO₂ (311 F g⁻¹), CC/Ni@MnO₂ (196.6 F g⁻¹), and CC@MnO₂ (186.1 F g⁻¹) at 1 A g⁻¹ and remarkable rate capability (367.5 F g⁻¹ at 10 A g⁻¹). Moreover, asymmetric supercapacitors constructed with CC/N-CNWs/Ni@MnO₂ as cathode material and activated carbon as anode material deliver an impressive energy density of 36.4 W h kg⁻¹ at a power density of 900 W kg⁻¹ and a good cycling life (72.8 % capacitance retention after 3500 cycles). This study paves a low-cost and simple way to design a hierarchical nanocomposite electrode with large surface area and superior electrical conductivity, which has wide application prospects in high-performance supercapacitors.     

Zn–Co Sulfide Microflowers Anchored on Three-Dimensional Graphene: A High-Capacitance and Long-Cycle-Life Electrode for Asymmetric Supercapacitors

Zinc–cobalt double-metal sulfides (ZCS) as Faradic electrode materials with high energy density have great potential for supercapacitors, but their poor transfer efficiency for electrons and ions hinders their electrochemical response. Herein, ZnCo₂(CO₃)_1.5(OH)₃@ZCS microflower hybrid arrays consisting of thin nanolayer petals were anchored on three-dimensional graphene (ZnCo₂(CO₃)_1.5(OH)₃@ZCS/3DG) by a simple hydrothermal method and additional ion-exchange process. A ZnCo₂(CO₃)_1.5(OH)₃@ZCS/3DG electrode delivered high capacitance (2228 F g⁻¹ at 1 A g⁻¹) and long cycling life (85.7 % retention after 17 000 cycles), which are ascribed to the multicomponent structural design. The 3DG conductive substrate improves the electron-transfer dynamics of the electrode material. Meanwhile, the microflowers consisting of thin nanolayer petals could not only provide many active sites for ions to improve the capacitance, but also alleviate the volume expansion to ensure the structural stability. Furthermore, an all-solid-state asymmetric supercapacitor based on a ZnCo₂(CO₃)_1.5(OH)₃@ZCS/3DG electrode achieved a high energy density of 27 W h kg⁻¹ at 528.3 W kg⁻¹ and exhibits exceptional cyclic stability for 23 000 cycles. Its ability to light a blue LED for 9 min verified the feasibility of its application for energy storage devices.     

Sb‐Triggered β‐to‐α Transition: Solvothermal Synthesis of Metastable α‐Cu2Se

Control over phase stabilities during synthesis processes is of great importance for both fundamental studies and practical applications. We describe herein a facile strategy for the synthesis of Cu₂Se with phase selectivity through a simple solvothermal method. In the presence and absence of SbCl₃, monoclinic α‐Cu₂Se and cubic β‐Cu₂Se can be synthesized, respectively. The formation of α‐Cu₂Se requires optimization of the Cu/Se molar ratio in the starting reagents, the reaction temperature, as well as the timing for the addition of SbCl₃. Differential scanning calorimetry of the synthesized α‐Cu₂Se has shown that a part of it undergoes a phase transition to β‐Cu₂Se at 135 °C, and that this phase transition is irreversible on cooling to ambient temperature. Kinetic studies have revealed that in the presence of Sb species the kinetically favored β‐Cu₂Se transforms to the thermodynamically favored α‐Cu₂Se. In this β‐to‐α phase transition process, the distribution of Cu ions in β‐Cu₂Se, as determined by the Cu/Se ratio and temperature, is likely to play a crucial role.     

Hydrothermal Synthesis of Nickel Oxide Nanosheets for Lithium‐Ion Batteries and Supercapacitors with Excellent Performance

Nickel oxide nanosheets have been successfully synthesized by a facile ethylene glycol mediated hydrothermal method. The morphology and crystal structure of the nickel oxide nanosheets were characterized by X‐ray diffraction, field‐emission SEM, and TEM. When applied as electrode materials for lithium‐ion batteries and supercapacitors, nickel oxide nanosheets exhibited a high, reversible lithium storage capacity of 1193 mA h g^?1 at a current density of 500 mA g^?1, an enhanced rate capability, and good cycling stability. Nickel oxide nanosheets also demonstrated a superior specific capacitance of 999 F g^?1 at a current density of 20 A g^?1 in supercapacitors.     

Microporous Carbon Nanofibers Derived from Poly(acrylonitrile-co-acrylic acid) for High-Performance Supercapacitors

Carbon nanofiber (CNF)-based supercapacitors have promising applications in the field of energy storage. It is desirable, but remains challenging, to develop CNF electrode materials with large specific surface area (SSA), high specific capacitance (SC), and high power density, as well as excellent cycling stability and high reliability. Herein, acrylonitrile–acrylic acid copolymer P(AN-co-AA) was synthesized for the preparation of nitrogen-doped microporous CNFs. Thermal degradation of the AA segment leads to the formation of micropores that are distributed not only on the CNF surface, but also inside the material. The microporous structure and nitrogen content can be manipulated at the molecular level by adjusting the weight ratio between AN and AA, and the SSA and SC could reach as high as 1099 m² g⁻¹ and 156 F g⁻¹, respectively. After KOH activation, the activated CNFs have an extremely high SSA of 2117 m² g⁻¹ and SC of 320 F g⁻¹, which are among the highest values ever reported for electric double-layer supercapacitors with an alkaline electrolyte. Furthermore, the capacitance retention, which can be maintained at 99 % even after 16 000 cyclic tests, reveals outstanding durability and repeatability.     

Shape‐Controlled Synthesis of NiCo2O4 Microstructures and Their Application in Supercapacitors

The shape‐controlled synthesis of NiCo₂O₄ microstructures through a facile hydrothermal method and subsequent calcinations was explored. By employing CoSO₄, NiSO₄, and urea as the starting reactants, flower‐like NiCo₂O₄ microstructures were obtained at 100 °C after 5 h without the assistance of any additive and subsequent calcination at 300 °C for 2 h; dumbbell‐like NiCo₂O₄ microstructures were prepared at 150 °C after 5 h in the presence of trisodium citrate and subsequent calcination at 300 °C for 2 h. The as‐prepared NiCo₂O₄ microstructures were characterized by X‐ray powder diffraction, field‐emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and (high‐resolution) transmission electron microscopy. Both the flower‐like and dumbbell‐like NiCo₂O₄ microstructures could be used as electrode materials for supercapacitors, and they exhibited excellent electrochemical performance, including high specific capacitance, good rate capability, and excellent long‐term cycle stability. Simultaneously, the shape‐dependent electrochemical properties of the product were investigated.     

Sodium‐Doped Mesoporous Ni2P2O7 Hexagonal Tablets for High‐Performance Flexible All‐Solid‐State Hybrid Supercapacitors

A simple hydrothermal method has been developed to prepare hexagonal tablet precursors, which are then transformed into porous sodium‐doped Ni₂P₂O₇ hexagonal tablets by a simple calcination method. The obtained samples were evaluated as electrode materials for supercapacitors. Electrochemical measurements show that the electrode based on the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets exhibits a specific capacitance of 557.7 F g^?1 at a current density of 1.2 A g^?1. Furthermore, the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets were successfully used to construct flexible solid‐state hybrid supercapacitors. The device is highly flexible and achieves a maximum energy density of 23.4 Wh kg^?1 and a good cycling stability after 5000 cycles, which confirms that the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets are promising active materials for flexible supercapacitors.     

Facile Synthesis of Nitrogen‐Doped Graphene Aerogels for Electrode Materials in Supercapacitors

Three‐dimensional porous nitrogen‐doped graphene aerogels (NGAs ) were synthesized by using graphene oxide (GO ) and chitosan (CS ) via a self‐assembly process by one‐pot hydrothermal method. The morphology and structure of the as‐prepared materials were characterized by means of scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, XPS spectroscopy, Raman spectroscopy, nitrogen adsorption/desorption measurement and Fourier transform infrared spectroscopy. The electrochemical performance of NGAs was studied by cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. The microstructure, surface area and capacitance of NGAs could be facilely controlled by adding different amounts of chitosan. The prepared NGA ‐4 showed a specific capacitance of 148.0 F/g at the discharge current density of 0.5 A/g and also retained 95.3% of the initial capacitance after 5000 cycles at the scan rate of 10 mV /s. It provided a possible way to obtain graphene based materials with high surface area and capacitance.     

Hexagonal FeNi2Se4@C Nanoflakes as High Performance Anode Materials for Sodium-ion Batteries

Metal selenides have drawn significant attention as promising anode materials for sodium-ion batteries(SIBs)owing to their high electronic conductivity and reversible capacity.Herein,hexagonal FeNi2Se4@C nanoflakes were synthesized via a facile one-step hydrothermal method.They deliver a reversible capacity of 480.7 mA·h/g at 500 mA/g and a high initial Coulombic efficiency of 87.8%.Furthermore,a discharge capacity of 444.8 mA·h/g can be achieved at 1000 mA/g after 180 cycles.The sodium storage mechanism of FeNi2Se4@C is uncovered.In the discharge process,Fe and Ni nanoparticles are generated and distributed in Na2Se matrix homogeneously.In the charge process,FeNi2Se4 phase is formed reversibly.The reversible phase conversion of FeNi2Se4@C during cycling is responsible for the excellent electrochemical performance and enables FeNi2Se4@C nanoflakes promising anode materials for SIBs.     

Facile Synthesis of A 3D Flower‐Like Mesoporous Ni@C Composite Material for High‐Energy Aqueous Asymmetric Supercapacitors

A 3D flower‐like mesoporous Ni@C composite material has been synthesized by using a facile and economical one‐pot hydrothermal method. This unique 3D flower‐like Ni@C composite, which exhibited a high surface area (522.4 m² g^?1), consisted of highly dispersed Ni nanoparticles on mesoporous carbon flakes. The effect of calcination temperature on the electrochemical performance of the Ni@C composite was systematically investigated. The optimized material (Ni@C 700) displayed high specific capacity (1306 F g^?1 at 2 A g^?1) and excellent cycling performance (96.7 % retention after 5000 cycles). Furthermore, an asymmetric supercapacitor (ASC) that contained Ni@C 700 as cathode and mesoporous carbon (MC) as anode demonstrated high energy density (60.4 W h kg^?1 at a power density of 750 W kg^?1).     

MnO2 Nanosheets Grown on Nitrogen‐Doped Hollow Carbon Shells as a High‐Performance Electrode for Asymmetric Supercapacitors

A hierarchical hollow hybrid composite, namely, MnO₂ nanosheets grown on nitrogen‐doped hollow carbon shells (NHCSs@MnO₂), was synthesized by a facile in situ growth process followed by calcination. The composite has a high surface area (251 m²g^?1) and mesopores (4.5 nm in diameter), which can efficiently facilitate transport during electrochemical cycling. Owing to the synergistic effect of NHCSs and MnO₂, the composite shows a high specific capacitance of 306 F g^?1, good rate capability, and an excellent cycling stability of 95.2 % after 5000 cycles at a high current density of 8 A g^?1. More importantly, an asymmetric supercapacitor (ASC) assembled by using NHCSs@MnO₂ and activated carbon as the positive and negative electrodes exhibits high specific capacitance (105.5 F g^?1 at 0.5 A g^?1 and 78.5 F g^?1 at 10 A g^?1) with excellent rate capability, achieves a maximum energy density of 43.9 Wh kg^?1 at a power density of 408 W kg^?1, and has high stability, whereby the ASC retains 81.4 % of its initial capacitance at a current density of 5 A g^?1 after 4000 cycles. Therefore, the NHCSs@MnO₂ electrode material is a promising candidate for future energy‐storage systems.     

Mo掺杂NiMnSe2的制备及其超级电容器性能

成分和结构是影响多元过渡金属硒化物电化学活性的关键因素。适当掺杂其他金属元素可以有效提高电极材料的电化学性能。通过简单的一步水热法,在泡沫镍上制备出了一种无黏结剂的Mo掺杂NiMnSe₂(记作Ni_0.8Mo_0.2MnSe₂)。Mo的少量掺杂为电极材料提供了丰富的反应活性位点,大大提高了NiMnSe₂的电化学性能。在1 A·g^-1时,Ni_0.8Mo_0.2MnSe₂的比容量达到1 404.0 F·g^-1。掺杂Mo显著降低了NiMnSe₂的电荷转移电阻和扩散电阻。组装的混合超级电容器Ni_0.8Mo_0.2MnSe₂//AC (活性炭)比容量达到81.6 F·g^-1,且倍率性能优异。在2 A·g^-1下连续充放电10 000周,容量保持率为95.8%,表现出超高的循环稳定性。混合超级电容器Ni_0.8Mo_0.2MnSe₂//AC在376.6 W·kg^-1的功率密度下,能量密度达25.5 Wh·kg^-1,高于NiMnSe₂//AC (17.3 Wh·kg^-1)。     

Mo掺杂NiMnSe2的制备及其超级电容器性能

成分和结构是影响多元过渡金属硒化物电化学活性的关键因素。适当掺杂其他金属元素可以有效提高电极材料的电化学性能。通过简单的一步水热法,在泡沫镍上制备出了一种无黏结剂的Mo掺杂NiMnSe₂(记作Ni_0.8Mo_0.2MnSe₂)。Mo的少量掺杂为电极材料提供了丰富的反应活性位点,大大提高了NiMnSe₂的电化学性能。在1 A·g^-1时,Ni_0.8Mo_0.2MnSe₂的比容量达到1 404.0 F·g^-1。掺杂Mo显著降低了NiMnSe₂的电荷转移电阻和扩散电阻。组装的混合超级电容器Ni_0.8Mo_0.2MnSe₂//AC (活性炭)比容量达到81.6 F·g^-1,且倍率性能优异。在2 A·g-1下连续充放电10 000周,容量保持率为95.8%,表现出超高的循环稳定性。混合超级电容器Ni_0.8Mo_0.2MnSe₂//AC在376.6 W·kg^-1的功率密度下,能量密度达25.5 Wh·kg^-1,高于NiMnSe2//AC (17.3 Wh·kg^-1)。     

Mo掺杂NiMnSe2的制备及其超级电容器性能

成分和结构是影响多元过渡金属硒化物电化学活性的关键因素。适当掺杂其他金属元素可以有效提高电极材料的电化学性能。通过简单的一步水热法,在泡沫镍上制备出了一种无黏结剂的Mo掺杂NiMnSe₂(记作Ni_0.8Mo_0.2MnSe₂)。Mo的少量掺杂为电极材料提供了丰富的反应活性位点,大大提高了NiMnSe₂的电化学性能。在1 A·g^-1时,Ni_0.8Mo_0.2MnSe₂的比容量达到1 404.0 F·g^-1。掺杂Mo显著降低了NiMnSe₂的电荷转移电阻和扩散电阻。组装的混合超级电容器Ni_0.8Mo_0.2MnSe₂//AC (活性炭)比容量达到81.6 F·g^-1,且倍率性能优异。在2 A·g^-1下连续充放电10 000周,容量保持率为95.8%,表现出超高的循环稳定性。混合超级电容器Ni_0.8Mo_0.2MnSe₂//AC在376.6 W·kg^-1的功率密度下,能量密度达25.5 Wh·kg^-1,高于NiMnSe₂//AC (17.3 Wh·kg^-1)。     

CoNi2S4上电沉积NiS用于柔性固态非对称超级电容器

采用一种在CoNi2S4上电沉积NiS的有效方法来改善钴/镍硫化物的性能。CoNi2S4@NiS电极材料在1 A·g^-1时比电容达到1433 F·g^-1,并具有很好的倍率性能。CoNi2S4@NiS和还原氧化石墨烯组装成的柔性固态非对称超级电容器的能量密度在功率密度为800 W·kg^-1时达到36.6 Wh·kg^-1,并且在10000次充放电后表现出良好的循环性能,循环保持率达87.8%。     

One-Pot Hydrothermal Synthesis of Ternary 1T-MoS2/Hexa-WO3/Graphene Composites for High-Performance Supercapacitors

A new ternary composite of 1T-molybdenum disulfide, hexagonal tungsten trioxide, and reduced graphene oxide (M-W-rGO) is synthesized by using a one-pot hydrothermal process. The synergetic effect of 1T-MoS₂ and hexa-WO₃ nanoflowers improves the electrochemical performance for supercapacitors by inducing additional active sites and hexagonal tunnels, respectively, which lead to high storage capacity and easy transfer of electrolyte ions. The ternary M-W-rGO composite has a high specific capacitance of 836 F g⁻¹ at 1 A g⁻¹, which is nearly twice that of binary composites of M-rGO and W-rGO with high capacitance retention of 86.35 % after 3000 cycles at a high current density of 5 A g⁻¹. This study provides a new ternary composite that can be used as an electrode material for high-performance supercapacitors.     

Hybrid Transition-Metal Oxide and Nitride@N-Doped Reduced Graphene Oxide Electrodes for High-Performance,Flexible, and All-Solid-State Supercapacitors

Nanoscale composites for high-performance electrodes employed in flexible, all-solid-state supercapacitors are being developed. A series of binder-free composites, each consisting of a transition bimetal oxide, a metal oxide, and a metal nitride grown on N-doped reduced graphene oxide (rGO)-wrapped nickel foam are obtained by using a universal strategy. Three different transition metals, Co, Mo, and Fe, are separately compounded with nickel ions, which originate from the nickel foam, to form three composites, NiCoO₂@Co₃O₄@Co₂N, NiMoO₄@MoO₃@Mo₂N, and NiFe₂O₄@Fe₃O₄@Fe₂N, respectively. These as-prepared active materials have similar regular variation patterns in their properties, including better conductivity and battery-mimicking pseudocapacitance, which result in their high whole-electrode capacitance performance [2598.3 F g⁻¹ (39.85 F cm⁻²), 3472.6 F g⁻¹ (41.43 F cm⁻²) and 1907.5 F g⁻¹ (3.41 F cm⁻²) for the composites incorporating Co, Mo, and Fe, respectively]. The as-assembled flexible, all-solid-state NiCoO₂@Co₃O₄@Co₂N//KOH/PVA//NiCoO₂@Co₃O₄@Co₂N device can be easily bent and exhibits high energy density and power density of 92.8 Wh kg⁻¹ and 1670.4 W kg⁻¹, respectively. The universality of this design strategy could allow it to be employed in producing hybrid materials for high-performance energy-storage devices.     

Hierarchical ZnCo2O4@NiCo2O4 Core–Sheath Nanowires: Bifunctionality towards High‐Performance Supercapacitors and the Oxygen‐Reduction Reaction

Increasing energy demands and worsening environmental issues have stimulated intense research on alternative energy storage and conversion systems including supercapacitors and fuel cells. Here, a rationally designed hierarchical structure of ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires synthesized through facile electrospinning combined with a simple co‐precipitation method is proposed. The obtained core–sheath nanostructures consisting of mesoporous ZnCo₂O₄ nanowires as the core and uniformly distributed ultrathin NiCo₂O₄ nanosheets as the sheath, exhibit excellent electrochemical activity as bifunctional materials for supercapacitor electrodes and oxygen reduction reaction (ORR) catalysts. Compared with the single component of either ZnCo₂O₄ nanowires or NiCo₂O₄ nanosheets, the hierarchical ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires demonstrate higher specific capacitance of 1476 F g^?1 (1 A g^?1) and better rate capability of 942 F g^?1 (20 A g^?1), while maintaining 98.9 % capacity after 2000 cycles at 10 A g^?1. Meanwhile, the ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires reveal comparable catalytic activity but superior stability and methanol tolerance over Pt/C as ORR catalyst. The impressive performance may originate from the unique hierarchical core–sheath structures that greatly facilitate enhanced reactivity, and faster ion and electron transfer.