Assembly of high-performance hybrid supercapacitors using FeCo2O4 microflowers as battery-type cathode materials

In this work, FeCo₂O₄ microflowers (MFs) and microparticles (MPs) were respectively prepared at different temperatures via a wet chemical method, along with a post annealing treatment in air. These MFs and MPs exhibited huge specific surface area and a large number of mesopores. Several electrochemical tests were conducted in a three-electrode configuration. The FeCo₂O₄ MFs delivered a specific capacity of 301.3C g^?1, higher than 253.9C g^?1 for FeCo₂O₄ MPs. A hybrid supercapacitor (HSC) device was assembled with FeCo₂O₄ as cathode and activated carbon (AC) as anode to investigate the practical applications in electrochemical energy storage. The FeCo₂O₄ MFs//AC HSC delivered a capacity of 107.2C g^?1 at 1 A g^?1 and an energy density (E_d) of 25.7 W h kg^?1 at 862.6 W kg^?1, respectively, while the FeCo₂O₄ MPs//AC HSC showed an E_d of 23.8 W h kg^?1 at the power density (P_d) of 878.9 W kg^?1. The two HSCs showed little capacity decay after 3000 cycles at 6 A g^?1. The capacity of FeCo₂O₄ MFs and the obtained E_d of HSC were in a high status among those of transition metal oxides (TMOs)-based electrodes reported earlier. The current synthetic strategy can be used as a reference to the synthesis of other similar electrochemical materials for HSC electrodes.     

Template-free synthesis of novel Co3O4 micro-bundles assembled with flakes for high-performance hybrid supercapacitors

In this paper, a novel Co₃O₄ micro-bundles structure (Co₃O₄ MBs) was obtained at 120 °C after a hydrothermal reaction for 24 h and followed by an annealing treatment at 300 °C in air. The unique Co₃O₄ MBs are constructed by many adjacent flakes with 0.4 μm in thickness, and exhibit a large surface area of 81.2 m² g^?1 and a mean pore diameter of 6.14 nm, which may facilitate a sufficient contact with electrolyte and then shorten the diffusion pathway of ions. A remarkable electrochemical behavior including specific capacity of 282.3 C g^?1 at 1 A g^?1 and 205.9 C g^?1 at 10 A g^?1, and an excellent cycling performance with 74.6% capacity retention after 4000 charge-discharge process at 5 A g^?1 are achieved when the test of Co₃O₄ MBs-modified electrode is performed using three-electrode configuration. Additionally, a hybrid supercapacitor (HSC) was fabricated with the obtained Co₃O₄ MBs as positive electrode and commercial activated carbon (AC) as negative electrode. The HSC exhibits a specific capacity of 144.1 C g^?1 at 1 A g^?1 and 126.4% capacity retention after 5000 cycles at 5 A g^?1. An energy density of 38.5 W h kg^?1 can be obtained at a power density of 962.0 W kg^?1, and 29.5 W h kg^?1 is still retained at 8532.5 W kg^?1. The simple synthetic strategy can be applicable to the synthesis of other transition metal oxides with superior electrochemical performance.     

MWCNTs-GONRs/Co3O4 electrode with needle-like arrays for outstanding supercapacitors

Multiwalled carbon nanotubes-graphene oxide nanoribbons (MWCNTs-GONRs) exhibit high specific surface area and good electroconductivity because of their unique three-dimensional cross-linking structure with the properties of both CNTs and GONRs. In this study, a hydrothermal method was employed to anchor MWCNTs–GONRs onto a Ni foam (NF) to obtain a precursor substrate. Subsequently, Co₃O₄ arrays were grown on the NF substrate to synthesize a MWCNTs–GONR/Co₃O₄ electrode. The electrode showed a capacitance of 846.2 F g⁻¹ at 1 A g⁻¹ and a capacitance retention of 90.1% after 3000 cycles. Furthermore, MWCNTs–GONRs/Co₃O₄ and active carbon (AC) were used as the positive and negative electrodes, respectively, to assemble a supercapacitor, which delivered a maximum energy density of 38.23 W h kg⁻¹ and a high power density of 6.80 kW kg⁻¹. In addition, the specific capacitance of the device reached a maximum of 91.5% after 9000 cycles. Thus, the MWCNTs–GONRs/Co₃O₄ electrode showed huge potential for supercapacitor applications.     

Three-dimensional carbon-based endogenous-exogenous MoO2 composites as high-performance negative electrode in asymmetric supercapacitors and efficient electrocatalyst for oxygen evolution reaction

It is not an easy way to design composite electrodes with a high concentration of the constituent. This study cleverly exploited the phase transformation of molybdenum oxide to synthesize three-dimensional carbon-based endogenous-exogenous MoO₂ composites (EEC) by a two-step process. MC-15 exhibited the most outstanding electrochemical performance among EEC, with a specific capacitance up to 411.1 F g^?1 in Na₂SO₄, due to the design of MoO₂, which could be highly loaded with three-dimensional carbon. In addition, the electrode capacitance remains up to 94.1% after 5000 cycles, attributed to the synergy effect of three-dimensional carbon and molybdenum dioxide by providing an abundance of active sites for MoO₂ and overcoming its stacking. In this way, the electrochemical properties of the EEC electrode are not compromised by the volume expansion during the electrochemical process. The energy density of the asymmetric supercapacitor using this material as the negative electrode and MnO₂@CC is 14 W h kg^?1 at a power density of 802 W kg^?1, showing a significant increase in energy density over the asymmetric supercapacitor with a conventional negative electrode (activated carbon, energy density of 3.36 W h kg^?1 and power density of 700 W kg^?1). Its specific capacitance remained 84.9% after 2500 cycles. In addition, an overpotential of only 348 mV was required to drive oxygen evolution in alkaline electrolytes with a Tafel slope as low as 88.7 mV dec^?1; the 20 h stability test retains almost 100%. The results show that the design optimization of the negative electrode material provides a simple and effective strategy to increase the energy density of supercapacitors, and EEC electrode materials are a great candidate to be utilized in supercapacitors with excellent performance as well as electrolytic water.     

Anchoring mesoporous Fe3O4 nanospheres onto N-doped carbon nanotubes toward high-performance composite electrodes for supercapacitors

Fe-based oxide electrodes for practical applications in supercapacitors (SCs) suffer from low conductivity and poor structural stability. To settle these issues, we report on the design and synthesis of Fe₃O₄/carbon nanocomposites via firmly anchoring mesoporous Fe₃O₄ nanospheres onto N-doped carbon nanotubes (N-CNTs) via C–O–Fe bonds. Mesoporous Fe₃O₄ nanospheres are featured by rich electroactive sites and short ion diffusion pathways. The N-CNTs, on the other hand, serve as the scaffolds, which not only provide conductive networks but also suppress the accumulation between mesoporous Fe₃O₄ nanospheres as well as alleviate volume changes during charge/discharge cycles. Accordingly, the constructed Fe₃O₄/N-CNTs nanocomposite electrode demonstrates improved specific capacity values of up to 314 C g⁻¹ at 1 A g⁻¹, with 92% retention of the initial capacity after 5000 cycles at 10 A g⁻¹. In addition, the assembled Fe₃O₄/N-CNTs//active carbon (AC) asymmetric supercapacitor (ASC) device possesses an energy density of 25.3 Wh kg⁻¹, suggesting that the prepared Fe₃O₄/N-CNTs nanocomposites are promising electrode materials for use in SCs.     

Novel and efficient hybrid supercapacitor of chemically synthesized quaternary 3D nanoflower-like NiCuCo2S4 electrode

In this work, we employed a simple and cost-effective chemical route to obtain a highly stable and efficient quaternary mesoporous 3D nanoflower-like NiCuCo₂S₄ nanocomposite for supercapacitor applications. The NiCuCo₂S₄ composite exhibited a mixture of NiCo₂S₄ and CuCo₂S₄ phases, confirming the formation a quaternary NiCuCo₂S₄ thin film. A surface morphological analysis revealed the unique nanoflower-like nanostructure of the annealed composite. The electrochemical analysis of the NiCuCo₂S₄ electrode demonstrated a high specific capacity (Cs) of 414 mAh g^?1 at a lower scan rate of 10 mV s^?1 and a superior cycling stability up to 3000 cycles. A solid-state hybrid supercapacitor (SHS) was also constructed by the NiCuCo₂S₄ and AC powder as positive and negative electrodes, respectively. The NiCuCo₂S₄//AC hybrid cell produced a high Cs, energy density, and power density of 159 F g^?1, 35.19 Wh kg^?1, and 0.66 kW kg^?1, respectively at a current density of 10 mA with good cycling stability. The results demonstrated that the fabrication process is effective for the development of a novel quaternary transition metal sulfide (TMS) electrode.     

Unique CNTs-chained Li4Ti5O12 nanoparticles as excellent high rate anode materials for Li-ion capacitors

Composite anode materials with a unique architecture of carbon nanotubes (CNTs)-chained spinel lithium titanate (Li₄Ti₅O₁₂, LTO) nanoparticles are prepared for lithium ion capacitors (LICs). The CNTs networks derived from commercial conductive slurry not only bring out a steric hindrance effect to restrict the growth of Li₄Ti₅O₁₂ particles but greatly enhance the electronic conductivity of the CNTs/LTO composites, both have contributed to the excellent rate capability and cycle stability. The capacity retention at 30 C (1 C = 175 mA g^?1) is as high as 89.7% of that at 0.2 C with a CNTs content of 11 wt%. Meanwhile, there is not any capacity degradation after 500 cycles at 5 C. The LIC assembled with activated carbon (AC) cathode and such a CNTs/LTO composite anode displays excellent energy storage properties, including a high energy density of 35 Wh kg^?1 at 7434 W kg^?1, and a high capacity retention of 87.8% after 2200 cycles at 1 A g^?1. These electrochemical performances outperform the reported data achieved on other LTO anode-based LICs. Considering the facile and scalable preparation process proposed herein, the CNTs/LTO composites can be very potential anode materials for hybrid capacitors towards high power-energy outputs.     

Polypyrrole-wrapped NiCo2S4 nanoneedles as an electrode material for supercapacitor applications

In this study, dicobalt tetrasulfide (NiCo₂S₄) nanoneedles were successfully synthesized by a two-step hydrothermal method on nickel foam. A layer of polypyrrole (PPy) was further wrapped on the surface of the NiCo₂S₄ nanoneedles by in-situ polymerization. The obtained NiCo₂S₄@PPy composite was investigated for supercapacitor applications, which exhibited a capacitance of 1842.8 F g^?1 at 1 A g^?1. An asymmetric supercapacitor device fabricated with an activated carbon negative electrode and NiCo₂S₄@PPy positive electrodes exhibited an energy density of 41.2 Wh kg^?1 at 402.2 W kg^?1 with a high charge–discharge cycling stability (92.8% after 5000 cycles). These results demonstrate that NiCo₂S₄@PPy electrodes have broad application prospects as energy storage electrode materials.     

Enhanced electrochemical performance of hybrid composite microstructure of CuCo2O4 microflowers-NiO nanosheets on 3D Ni foam as positive electrode for stable hybrid supercapacitors

Self-assembled composite porous structures comprising CuCo₂O₄ microflowers and NiO hexagonal nanosheets were synthesized on a conducting 3D Ni foam surface [CCO/NO] using a simple hydrothermal method. This unique composite assembly was further characterized and electrochemically evaluated as a binder-free positive electrode for hybrid supercapacitor application. The study showed that the CCO/NO exhibited a maximum areal capacitance of 1444 mF cm^?2, significantly higher than the parent CuCo₂O₄ and NiO electrodes, with remarkable stability of 88.5% for 10,000 galvanostatic charge-discharge cycles. Key features for the enhanced electrochemical performance of CCO/NO can be related to a lowered diffusion resistance because the hybrid nanocomposite porous assembly generates short diffusion paths for electrolyte ions and more active sites for reversible faradaic transition for charge storage. The hybrid supercapacitor was assembled using activated carbon as a negative electrode and CCO/NO as a positive electrode in alkaline electrolyte, performed at an improved potential of 1.6 V. Device showed a maximum areal capacitance of 122 mF cm^?2, a maximum areal energy density of 43 μWh cm^?2, and a maximum areal power density of 5.1 mW cm^?2. This hybrid supercapacitor showed remarkable cyclic stability up to 98% for 10,000 cycles. This study encourages the development of low-cost, high-performance, durable electrode designs using hybrid composite for next-generation energy storage systems.     

Electrochemical behavior of CuO/rGO nanopellets for flexible supercapacitor,non-enzymatic glucose,and H2O2 sensing application

In the present article, graphene oxide (GO) sheets and monoclinic copper oxide (CuO) nanocrystals are connected with each other and result in the formation of CuO/rGO nanopellets, and these nanopellets synthesized using coprecipitation method. The nanopellet structured CuO/rGO composite on carbon cloth, which act as current collector exhibits specific capacitance of 188 F g^?1 at a current density of 0.2 A g^?1 and up to 96.3% capacity retention after 2000 charge-discharge cycles. It shows a maximum energy density of 7.32 Wh kg^?1 and power density of 53 W kg^?1. The glucose sensing characteristics of CuO/rGO nanopellet is investigated on carbon cloth and ITO substrate. It shows glucose sensitivity of 0.805 mA mM^?1 cm^?2 and 0.2982 mA mM^?1 cm^?2 for a bundle like structured CuO/rGO composite on carbon cloth and ITO substrate, respectively. Further H₂O₂ sensing is studied on ITO substrate, which manifests H₂O₂ sensitivity of 84.39 μA mM^?1 cm^?2. The results indicate that nanopellet structured CuO/rGO composite could be a promising electrode material for supercapacitor, glucose, and H₂O₂ sensor.     

Construction of pseudocapacitive Li2-xLaxZnTi3O8 anode for fast and super-stable lithium storage

Lithium-ion capacitors (LICs) composed of battery-type anodes with large energy densities and capacitor-type cathodes with high power densities are considered as appealing energy-storage devices. Here, a LIC with good performance is constructed using active carbon (AC) as the cathode and Li_1.95La_0.05ZnTi₃O₈ (LL5ZTO) as the anode. LL5ZTO doped with La is synthesized via a one-step solid-state route. The kinetics and structural stability of LZTO are enhanced by La-doping. Thus, LL5ZTO exhibits good Li-storage performance. The discharge specific capacity reaches 182.6 mAh g^?1 at 3 A g^?1 (120th cycle) for LL5ZTO. The LIC based on the LL5ZTO anode and the AC cathode delivers an energy density of 59.72 Wh kg^?1 at 846.4 W kg^?1, and a high power density of 8771 W kg^?1 at 19.49 Wh kg^?1. Furthermore, the capacity retention is over 90% after 3000 cycles for the LIC at 2 A g^?1. The good electrochemical performance indicates that the constructed LIC is expected to use in advanced energy storage devices.     

MOFs derived (Ni0.75Co0.25)Se2 nanoparticles embedded in N-doped nanocarbon for hybrid supercapacitors

Bimetallic selenides have aroused great interest as the electroactive materials for energy storage because of their high conductivity, robust electrochemical activity, and the synergistic effect. Herein, (Ni_0.75Co_0.25)Se₂ nanoparticles embedded in N-doped nanocarbon ((Ni_0.75Co_0.25)Se₂@NC) hybrids were derived from nickel and cobalt bimetal-organic frameworks (NiCo-MOFs), which were synthesized by ethylene glycol solvothermal method. Due to the synergistic contributions and unique architecture, (Ni_0.75Co_0.25)Se₂@NC hybrids electrode presents a considerable specific capacity of 536.6 C g^?1 at a discharge current density of 1 A g^?1. In addition, an as-assembled (Ni_0.75Co_0.25)Se₂@NC//activated carbon (AC) hybrid supercapacitor (HSC) ((Ni_0.75Co_0.25)Se₂@NC//AC HSC) shows large specific capacitance (73.6 F g^?1 at 0.5 A g^?1), outstanding energy density (26.2 Wh kg^?1 at 400 W kg^?1) with superior cyclic performance (88.7% of capacity retention after 5000 cycles). Furthermore, a (Ni_0.75Co_0.25)Se₂@NC//AC device could drive a mini-fan running for 67 s. Thus, (Ni_0.75Co_0.25)Se₂@NC is an outstanding active material for electrochemical energy storage.     

Electrochemical storage mechanism of interstratification-assembled Ti3C2Tx MXene/NiCo-LDHs electrode in alkaline,acid and neutral electrolytes

Different kinds of two-dimensional hybrid electrodes have high theoretical capacitance and energy density. However, the origin of the electrochemical storage mechanism still remains elusive in alkaline, acid and neutral electrolytes. Herein, the interstratification-assembled Ti₃C₂T_x MXene/NiCo-LDHs electrodes were successfully prepared and studied in different electrolytes by in-situ Raman spectroscopy. The results show that H₂O molecules in neutral electrolyte combine with –OH at the end of Ti₃C₂T_x MXene during charging, and debonding occurs during discharge. Similarly, this reaction also occurs in the discharge process with NiCo-LDHs and provides smaller pseudocapacitance characteristics. Although this pseudocapacitance reaction also occurs in acidic and alkaline electrolytes, however, the difference is that the hydrogen ions will promote the electrochemical performance of Ti₃C₂T_x MXene and has a certain corrosion consumption effect on NiCo-LDHs, but generally improve the electrochemical performance of Ti₃C₂T_x MXene/NiCo-LDHs. Interestingly, the OH^? in alkaline electrolyte can promote the electrochemical performance of NiCo-LDHs, and produce a new electrochemical reaction with –F between the layers of Ti₃C₂T_x MXene, which greatly improves the overall electrochemical performance of this hybrid electrodes. As a result, Ti₃C₂T_x MXene/NiCo-LDHs electrodes have the best electrochemical performance in alkaline electrolyte with capacitance of 283 F g^?1, energy density of 14.2 Wh kg^?1 and power density of 3007.1 W kg^?1. This work lays a foundation for the preparation of high-performance two-dimensional hybrid electrochemical energy storage devices.     

Interface bonding engineering for constructing a battery-type supercapacitor cathode with ultralong cycle life and high rate capability

The low rate and poor cycle greatly limit the large-scale applications of supercapacitors electrodes in energy storage field. In this work, the SnS₂/Ni₃S₂ nanosheets arrays are bonded on N/S co-doped graphene nanotubes though N–Sn/Ni and S–Sn/Ni interface bonds employing a simple hydrothermal method to form a self-supported battery-type supercapacitors cathode. A series of characterization and DFT calculations indicate that the interface bonding not only automatically generates the internal electric field and allows more redox reactions to carry out easily, but also effectively reduces the OH^? ions adsorption energy and maintains the integration of the electrode structure. This unique design greatly promotes the electronics/ions transfer and reaction kinetics of the cathode, and substantially enhances its rate capability and durability. Detailedly, a high specific capacity of 296.9 mAh g^?1 at 2 A g^?1 is obtained. More impressively, the cathode still holds 155.6 mAh g^?1 when the current density is enlarged to 100 A g^?1, as well as it can retain 84% initial capacity over 50,000 cycles. Besides, an assembled asymmetric supercapacitor utilizing the prepared N/S-GNTs@B–SnS₂/Ni₃S₂ nanosheets arrays cathode and activated carbon anode presents a large energy density of 51 W h kg^?1 at 850 W kg^?1 and outstanding cycling stability. This work provides an effective strategy for improving rate capability and cycle lifespan of battery-type supercapacitors electrodes, and pushes the metal compounds forward a significant step in the practical applications of energy storage devices.     

Enhanced ions and electrons transmission enables high-performance KxMnO@C cathode for hybrid supercapacitors

Manganese oxides have been regarded as one of the most promising electrode materials for energy storage systems. Especially, they can be used as battery-type electrodes in hybrid supercapacitors to achieve high energy density and power density at the same time. In such an application, the redox reaction on the battery-type electrodes needs to speed up to match the fast charging-discharging process of the counter capacitive electrodes. Herein, we intercalated K⁺ ions into MnO₂ to enlarge the interlayer space as channels for ion diffusion, and coated the particles with carbon layer to achieve fast charging/discharging ability. The obtained K_xMnO@C particles delivered a high specific capacitance of 1039 F g^?1 in 5 M LiTFSI aqueous electrolyte. Coupled with activated carbon anode, the hybrid supercapacitor showed outstanding energy and power density.     

Electrodeposited PbO2 thin film as positive electrode in PbO2/AC hybrid capacitor

Lead dioxide (PbO₂) thin films were prepared on Ti/SnO₂ substrates by means of electrodeposition method. Galvanostatic technique was applied in PbO₂ film formation process, and the effect of deposition current on morphology and crystalline form of the PbO₂ thin films was studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The energy storage capacity of the prepared PbO₂ electrode was investigated by means of cyclic voltammetry (CV) and charge/discharge cycles, and a rough surface structure PbO₂ film was selected as positive electrode in the construction of PbO₂/AC hybrid capacitor in a 1.28 g cm⁻³ H₂SO₄ solution. The electrochemical performance was determined by charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results showed that the PbO₂/AC hybrid capacitor exhibited high capacitance, good cycling stability and long cycle life. In the voltage range of 1.8-0.8 V during discharge process, considering the weight of all components of the hybrid capacitor, including the two electrodes, current collectors, H₂SO₄ electrolyte and separator, the specific energy and power of the device were 11.7 Wh kg⁻¹ and 22 W kg⁻¹ at 0.75 mA cm⁻², and 7.8 Wh kg⁻¹ and 258 W kg⁻¹ at 10 mA cm⁻² discharge currents, respectively. The capacity retains 83% of its initial value after 3000 deep cycles at the 4 C rate of charge/discharge.     

Facile fabrication of flower-like binary metal oxide as a potential electrode material for high-performance hybrid supercapacitors

Developing efficient electrode material with rational design and structure remains a crucial and great challenge for the significant improvement of high-performance hybrid supercapacitors (HSCs). Particularly, the performance of the HSCs can be largely enhanced by designing the battery-type Faradaic material with well-defined morphology and defective engineering. Here, a facile and effective strategy is utilized to develop oxygen-deficient flower-like three-dimensional NiMoO_4?δ (O_d-NMO) nanomaterial via hydrothermal process and following thermal-treatment under an inert-gas atmosphere. The presence of oxygen deficiency in the O_d-NMO is evaluated utilizing various spectroscopy techniques by comparing the pristine NiMoO₄ (P-NMO) heat treated under an ambient atmosphere. The electrochemical studies indicate that the oxygen defect sites in the O_d-NMO electrode have a considerable role in the betterment of supercapacitive performances. Hence, the O_d-NMO electrode provides a large specific capacity of 789 mA h g^?1 at 1 A g^?1 with an excellent rate capability than the P-NMO (579 mA h g^?1). Besides, the fabricated HSC based on O_d-NMO flower and activated carbon as the positive and negative electrodes, delivers a specific capacitance as high as 153 F g^?1 and accomplishes a large energy density (47.76 W h kg^?1) and power density (51.69 kW kg^?1) with improved long-term stability.     

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.     

Al-doping driven electronic structure of α-NiS hollow spheres modified by rGO as high-rate electrode for quasi-solid-state capacitor

Developing an optimized electronic structure of α-NiS electrode material is critical for its high-rate electrochemical performance of quasi-solid-state capacitor. Herein, Al³⁺ have been doped into α-NiS lattice and the reduced graphene oxide (rGO) is employed to modify Al-doping α-NiS, to alleviate the low-mobility charge of α-NiS. The electronic structure and electrochemical properties of α-NiS hollow spheres induced by Al-doping and rGO modification are investigated, both experimental characterization and theoretical results confirm Al-doping affect the electronic structure and electrochemical performance of α-NiS hollow spheres. In the composite of Al-doping α-NiS and rGO (named as Al_xNi_1-xS/rGO), the doped heteroatom improves the intrinsic electronic structure of α-NiS and the rGO provides a good electric conducting network, leading to an enhanced electrochemical performance of α-NiS as high-rate electrode material. After evaluation, the optimized Al_0.2Ni_0.8S/rGO composite shows a superior reversible capacity of 1096 C g^?1 at 2 A g^?1, and retains a capability of 471 C g^?1 at a high-rate of 30 A g^?1. Moreover, an asymmetric quasi-solid-state hybrid capacitors assembled by Al_0.2Ni_0.8S/rGO and activated carbon presents a high energy density of 30.6 Wh kg^?1. This work provides a foundational strategy for the modification of α-NiS through Al-doping and combining with rGO, which has a positive effect on α-NiS electrode material in quasi-solid-state hybrid capacitors.     

Carbon/PbO2 asymmetric electrochemical capacitor based on methanesulfonic acid electrolyte

A new hybrid electrochemical capacitor based on an activated carbon negative electrode, lead dioxide thin film and nanowire array positive electrode with an electrolyte made of a lead salt dissolved in methanesulfonic acid was investigated. It is shown that the maximum energy density and specific capacity of the C/PbO₂ nanowire system increase during the first 50 cycles before reaching their maximum values, which are 29 Wh kg⁻¹ and 34 F g⁻¹, respectively, at a current density of 10 mA cm⁻² and a depth of discharge (positive active electrode material) of 3.8%, that corresponds to a 22C rate. This is 7–8 times higher than the corresponding maximum values reached with a C/PbO₂ thin film cell operated in the same conditions. After an initial activation period, the performances of the C/PbO₂ nanowire system stay constant and do not show any sign of degradation during more than 5000 cycles. For comparison, the C/PbO₂ thin film system exhibits a 50% decrease of its performances in similar conditions.