MXene nanosheets decorated with MoP nanoparticles as high-performance supercapacitor material

Supercapacitor is a promising energy storage device, which has many advantages including long service lifetime, great power density, fast charge-discharge processes, and green environmental protection. The properties and performance of supercapacitors are greatly dependent on the electrode materials; hence the selection of the electrode material is crucial. There are many metal oxides which have been reported for supercapacitors and ultracapacitors; however, its performance is not that as expected. Thus high-performance electrode materials with large surface area and specific capacitance have been a topic of interest for the development of high-performance supercapacitors. Recently, two-dimensional (2D) transition metal dichalcogenides having layered structures, such as MoS2, VS2, SnS2, CoS2, and WS2, have received significant attention because they offer good energy density, power density, and cycling stability. Among them, the layered molybdenum disulfide (MoS2) is considered to have great potential for its applications as supercapacitors. MoS2 nanosheet is composed of one Mo atomic layer sandwiched between two S layers by covalent bonding, and with these triple layers stacked together to form a layered structure, is expected to act as an excellent energy storage material. It is because of the 2D electron–electron correlations among Mo atoms which would aid in enhancing planar electric transportation properties. MoS2 nanosheets can deliver excellent pseudocapacitance because of the Mo ions having oxidation states ranging from +2 to +6, which enable them to be used as high-performance electrode materials in supercapacitors. Indeed, as a graphene analogue, MoS2 nanosheets exhibit unique physical, optical, and electrical properties correlated with its 2D ultra-thin atomic layer structure and high surface area, making it very interesting for its use as electrodes in high-performance supercapacitors and also a promising supporting material to stabilize metal nanoparticles (NPs), forming hierarchical composites. The specific capacitance of MoS2 is still very limited in alone for energy storage applications. The combination of MoS2 and other conducting materials such as graphene, carbon nanotubes (CNTs), or ceramic nanomaterials such a zirconium (Zr) may overcome these deficiencies. This chapter gives a clear picture of the applications of MoS2 as high-performance electrode in supercapacitors.

Nanoporous CuS nano-hollow spheres as advanced material for high-performance supercapacitors

Nickel compounds, especially Ni(HCO3)2 (here denoted as NiC), have been widely combined with other materials to obtain composites with a more favorable structure that exhibit excellent electrochemical performance as supercapacitors. Unfortunately, the complicated processes for preparing such composites directly restrict their further application. Herein, we prepared a NiC/nickel tetraphosphate (Ni(P4O11)) nanocomposite (NiC/NiP) by introducing ions into the NiC reaction system; this composite can be applied in high-performance supercapacitors. The micromorphology of NiC/NiP material displayed an appropriate combination of NiP nanowires and thin NiC nanosheets, which provide sufficient active sites, short ion diffusion paths and fast ion diffusion speeds. NiC/NiP material exhibited an excellent rate performance of 70.2% retained capacity, although the current was increased by 15 times (1196 F g−1 at 2.0 A g−1 and 840 F g−1 at 30 A g−1). The energy density of a NiC/NiP//active carbon (AC) asymmetric supercapacitor fabricated in 6 M KOH was as much as 39.02 W h kg−1 and 26.67 W h kg−1 under corresponding power densities of 160 W kg−1 and 8000 W kg−1, respectively. The asymmetric supercapacitor delivered a stable cyclic performance of 78% capacitive retention after 5000 continuous charge/discharge cycles. More importantly, a 2.5 V light-emitting diode was lit successfully by two NiC/NiP//AC asymmetric supercapacitors in series. These results confirm that NiC/NiP nanocomposite has great potential in practical applications of electrochemical energy storage devices.

Blue TiO2 nanosheets as a high-performance electrode material for supercapacitors

Novel ZnFe2O4@MnO2@MXene composites with ultrathin thickness and excellent electromagnetic absorption performance

N/S co-doped interconnected porous carbon nanosheets as high-performance supercapacitor electrode materials

The interaction between cathode and anode materials is critical for developing a high-performance asymmetric supercapacitor (SC). Significant advances have been made for cathode materials, while the anode is comparatively less explored for SC applications. Herein, we proposed a high-performance binder-free anode material composed of two-dimensional ZnFe2O4 nanoflakes supported on carbon cloth (ZFO-NF@CC). The electrochemical performance of ZFO-NF@CC as an anode material for supercapacitor application was examined in a KOH solution via a three-electrode configuration. The ZFO-NF@CC electrode demonstrated a specific capacitance of 509 F g−1 at 1.5 A g−1 and was retained 94.2% after 10,000 GCD cycles. The ZFO-NF@CC electrode showed exceptional charge storage properties by attaining high pseudocapacitive-type storage. Furthermore, an asymmetric SC device was fabricated using ZFO-NF@CC as an anode and activated carbon on CC (AC@CC) as a cathode with a KOH-based aqueous electrolyte (ZFO-NF@CC||AC@CC). The ZFO-NF@CC||AC@CC yielded a high specific capacitance of 122.2 F g−1 at a current density of 2 A g−1, a high energy density of 55.044 Wh kg−1 at a power density of 1801.44 W kg−1, with a remarkable retention rate of 96.5% even after 4000 cycles was attained. Thus, our results showed that the enhanced electrochemical performance of ZFO-NF@CC used as an anode in high-performance SC applications can open new research directions for replacing carbon-based anode materials.

To develop high-performance electrode materials for aqueous potassium-ion hybrid supercapacitors (APICs), a bimetallic metal-organic framework (MOF), CuNi-KHP (KHP = potassium hydrogen phthalate), was prepared via a solvothermal method. The material features a 3D architecture constructed by stacking 2D nanosheets, with Cu/Ni bimetallic nodes and a multi-layered structure. Potassium ions were pre-inserted into the MOF using potassium hydrogen phthalate as the ligand, which regulates interlayer interactions and creates hierarchical pores for ion transport. Electrochemical characterization studies show that CuNi-KHP exhibits a high specific capacitance of 1568.58 F g-1 at 0.5 A g-1, accompanied by an energy density of 50.52 Wh kg-1 and a power density of 676.12 W kg-1. It also maintains 90.1% capacity retention after 10 000 cycles. The assembled CuNi-KHP//AC hybrid PIC delivers an energy density of 76 Wh kg-1 and a power density of 812 W kg-1 at 0.5 A g-1, with a capacity retention efficiency of 75% after 10 000 cycles at 1 A g-1. These results demonstrate that CuNi-KHP is a promising cathode material for high-performance PICs, owing to its synergistic bimetallic effect and K+-regulated porous structure.

Spinel NiCo2O4 based hybrid materials for supercapacitors: Recent developments and future perspectives

With rapid advancements in renewable energy harvesters and flexible electronics, there is a dire need to develop energy storage devices (EEDs) that respond well to these applications. Supercapacitors are a type of EEDs with higher energy and power densities. This, combined with their ultra high cycle life makes them an attractive candidate to be used both as a standalone or coupled with other EEDs. The active material in supercapacitors can be broadly classified into three types: carbonaceous, conductive polymer, and metal oxides. Each category of materials has its own advantages and drawbacks. It is reasonable to formulate a ternary composite such that the advantage of one material effectively suppresses the drawback of the other. Herein, a ternary hierarchical microsphere (TMS) composed of polyaniline nanofibers, CeO2 nanorods, and reduced graphene is obtained through a simple and highly scalable spray-drying technique. The synthesized TMS was physiochemically characterized using XRD, FTIR, SEM, XPS, and gas adsorption surface analysis. Electrochemical analysis revealed that the optimized TMS possess high specific capacity (685 F g-1), good rate performance and excellent cycle life (~90% capacitance retention after 6000 cycles). An asymmetric device constructed using the TMS and rGO revealed a high specific energy density (46.3 W h kg-1) at a power density of 850 W kg-1 with a very stable cyclic performance. Thus, we demonstrate a simple yet effective strategy to produce high-performance supercapacitor material, which is highly scalable for industrial-scale production.

Copper oxide/cuprous oxide/hierarchical porous biomass-derived carbon hybrid composites for high-performance supercapacitor electrode

Spray drying-assisted preparation FeSx/C/CNT composite for energy storage and conversion performance

Facile design and synthesis of nickle-molybdenum oxide/sulfide composites with robust microsphere structure for high-performance supercapacitors

Perovskite oxides have attracted significant attention as capacitor electrode materials owing to their unique physical and electronic properties. In this paper, a novel La0.7Sr0.3CoO3-δ (LSC)@MnO2 core–shell nanorod was synthesized by controlled electrospinning combined with hydrothermal synthesis. The LSC, as a typical perovskite-type material, with excellent stability and ion–electron double conductivity, can perfectly serve as conductive backbone. Grid-like MnO2 nanosheets are grown on LSC to form a unique core/shell nanostructure, could effectively improve the electrochemical performance of MnO2. The grid-like MnO2 nanosheets shell significantly increase the effective area over which the reaction may take place and reduce the ion/electron transmission distance, which is beneficial in that it shifts in ions and electrons, enhancing the electrochemical reaction kinetics thereof. LSC@MnO2 core/shell nanorods demonstrated good electrochemical performance with high capacitance (570 F g−1 at 1 A g−1), and revealed excellent cycling stability (capacitance retention remains at 97.2% after 5000 cycles). The asymmetric supercapacitor device (LSC@MnO2//AC) displayed a desirable energy density of 37.6 W h kg−1 at 375 W kg−1, and still remains at 23.3 W h kg−1 at a high power density of 7489.3 W kg−1, indicating that the LSC@MnO2 nanorods are an outstanding pseudo-capacitive electrode material, with significant potential for application in high-performance supercapacitors.

Exploring high-performance and low-priced electrode materials for supercapacitors is important but remains challenging. In this work, a unique sandwich-like nanocomposite of reduced graphene oxide (rGO)-supported N-doped carbon embedded with ultrasmall CoNiSx nanocrystallites (rGO/CoNiSx/N-C nanocomposite) has been successfully designed and synthesized by a simple one-step carbonization/sulfurization treatment of the rGO/Co-Ni precursor. The intriguing structural/compositional/morphological advantages endow the as-synthesized rGO/CoNiSx/N-C nanocomposite with excellent electrochemical performance as an advanced electrode material for supercapacitors. Compared with the other two rGO/CoNiOx and rGO/CoNiSx nanocomposites, the rGO/CoNiSx/N-C nanocomposite exhibits much enhanced performance, including a high specific capacitance (1028.2 F g-1 at 1 A g-1), excellent rate capability (89.3% capacitance retention at 10 A g-1) and good cycling stability (93.6% capacitance retention over 2000 cycles). In addition, an asymmetric supercapacitor (ASC) device based on the rGO/CoNiSx/N-C nanocomposite as the cathode and activated carbon (AC) as the anode is also fabricated, which can deliver a high energy density of 32.9 W h kg-1 at a power density of 229.2 W kg-1 with desirable cycling stability. These electrochemical results evidently indicate the great potential of the sandwich-like rGO/CoNiSx/N-C nanocomposite for applications in high-performance supercapacitors.