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MXenes are the typical ions insertion-type two-dimensional (2D) nanomaterials, have attracted extensive attention in the Li

Aqueous zinc ion batteries (ZIBs) are widely researched due to the low-cost and intrinsic safety. However, the rate capability and specific capacity of ZIBs is limited due to the dissolution and structural collapse of cathode materials. It is crucial to construct stable cathode materials to promote rate capability and cycle stability of ZIBs. In this paper, The V3O7 was tightly attached to the surface of graphene oxide (GO) by a hydrothermal reaction and a V3O7/GO heterostructure was successfully achieved. The GO could increase structural stability, enhance electrical conductivity, and expand specific surface area of V3O7. Therefore, the V3O7/GO with a heterostructure exhibits an improved cycle stability and rate capability compared with V3O7. It displayed a specific capacity of 275.6 mA h g−1 at a current density of 1.0 A g−1. The study paves the way for promoting the Zn2+ storage performance of vanadium oxide and developing stable cathode materials of ZIBs.

2D materials is a promising Na+ insertion-type material due to its unique layered structure, however, the long diffusion channels yielded by stacking limited the Na+ storage rate capability. Herein, a 3D MoS2–Ta4C3 heterostructure (M-Ta4C3) composite is designed by supported 2D MoS2 nanosheets on/in the surface/interlayers of 2D Ta4C3 matrix for achieving high rate Na+ storage. The 2D MoS2 nanosheets is confined in the interlayers of Ta4C3 matrix that can avoid the stacking and expand the interlayer spacing of Ta4C3 matrix, which enlarges the contact surface area between electrode and electrolyte, and exposes more electrochemical active sites for Na+ storage. The Ta4C3 matrix improves the conductivity, prevents the aggregation and confines the volume expansion of MoS2 nanosheets which optimizes the structure stability and provides short Na+ diffusion channels. The M-Ta4C3 exhibits a larger interlayer spacing of 1.69 nm, extraordinary electrochemical performance and outstanding rate capability which benefitted from the 3D heterostructure. The M-Ta4C3//AC SIC owns super energy and power densities of 87.6 Wh kg−1 and 3937.3 W kg−1. This work employs Ta4C3 MXene as a Na+ storage material for the first time, and it provides an idea to improve the Na+ storage performance of 2D materials by constructing a 3D heterostructure.

Nanofibers with hollow or porous network structure have numerous prospective realistic applications in electrode materials of a hybrid supercapacitor. Herein, La0.7Sr0.3CoO3/Co3O4 nanofibers (LSC/Co3O4 NFs) with hollow network porous structure where Co3O4 nanoparticles evenly distributed in the LSC single tube both sides of hollow are successfully prepared by one-step electrospinning. Electrochemical characteristics of LSC-doped composite electrode materials with different proportions have studied in detail. The result showed the LSC (20 wt%)/Co3O4 electrode material displayed the eminent specific capacity of 215 C g-1 (430 F g-1) at 1 A g-1. Furthermore, the LSC (20 wt%)/Co3O4//AC hybrid supercapacitor showed remarkable cyclic stability after 5000 cycles with a capacity retention of 86.3% and it showed a tremendous energy density of 21.9 Wh kg-1 at a power density of 358.4 W kg-1. Hence, the prepared LSC/Co3O4 NFs have promised a new type of electrode for hybrid supercapacitors.

Surface modification of oxygen evolution reaction (OER) cocatalysts is a promising approach to improve PEC water oxidation activity by accelerating the surface charge injection efficiency and catalytic reaction kinetics. However, the PEC performance is still restricted by inefficient charge transfer at the semiconductor/cocatalyst interface. In this study, ultrathin Ti3C2 nanosheets, serving as a highly efficient hole transport layer, were introduced into the Fe2O3/CoAl-layered double hydroxide (LDH) interface. The obtained Fe2O3–Ti3C2–CoAl photoanodes exhibited a significantly improved photocurrent density of 2.1 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE) under AM 1.5G illumination. In this system, the Ti3C2 nanolayer not only suppresses the interfacial recombination of photogenerated carriers but also facilitates efficient hole transfer from Fe2O3 to the OER cocatalyst, thus promoting the PEC performance. This study provides a new guideline for optimizing the charge transfer at the semiconductor/cocatalyst interface.

Molybdenum carbide (Mo2C) is an attractive candidate as the electrode active material of supercapacitors (SCs) due to its low cost, outstanding electrical conductivity and superior chemical stability; however, the aggregation of Mo2C nanoparticles impedes its applications. Herein, zero-dimensional (0D) Mo2C nanoparticles are anchored on three-dimensional (3D) octahedral amorphous carbon (3DPO-Mo2C/C) by a mild and effective method with carbonizing and etching the Cu/Mo-based metal–organic framework. The 3DPO-Mo2C/C displays a large specific surface area, abundant mesopores and stable 3D structure, which not only expose more active reaction sites and shorten diffusion paths for electrolyte ions, but also prevent the aggregation and improve the structure stability of Mo2C nanoparticles. It exhibits an outstanding specific capacitances of 110 and 105 F g−1 in the electrolytes of 6 M KOH and 2 M EMIMA/AN. Employing the active carbon (AC) as counter electrode to assemble a SC with 3DPO-Mo2C/C as work electrode, which delivers higher energy and power densities of 12 Wh kg−1 and 1620 W kg−1, and the specific capacitance remains 91.3% after 6000 cycles. This approach not only prevents the aggregation of Mo2C nanoparticles successfully but also provides a possibility for Mo2C to be used in SCs.

The high cost and platinum dissolution issues of counter electrodes (CEs) are two core problems for the development of dye-sensitized solar cells (DSSCs). In this work, different CEs based on binary alloy Ru81.09Co18.91, Ru80.55Se19.45 and Co20.85Se79.15 nanostructures for DSSCs were successfully synthesized and investigated by a facile and environmentally friendly approach. Here, we found that the Co20.85Se79.15 alloy CE-based device yields the higher photoelectric conversion efficiency of 7.08% compared with that (5.80%) of the DSSC using a pure Pt CE because of the larger number of active sites with improved charge transferability and reduced interface resistance by matching work function with the I3‒/I‒ redox electrolyte. The inexpensive synthesis method, cost-effectiveness and superior catalytic activity of the Co20.85Se79.15 alloy may open up a new avenue for the development of CEs for DSSCs in the near future.

High cost and instability of platinum (Pt) counter electrodes (CEs) are two persistent issues in dye-sensitized solar cells (DSSCs). Here, ternary selenide RuCoSe and NiCoSe-nanostructured CEs are ...

In this study, we, for the first time, demonstrate a general solid-phase pyrolysis method to synthesize hybrid transition metal nanocrystal-embedded graphitic carbon nitride nanosheets, namely M-CNNs, as a highly efficient oxygen electrocatalyst for rechargeable Zn–air batteries (ZABs). The ratios between metallic acetylacetonates and the g-C3N4 precursor can be controlled where Fe-CNNs−0.7, Ni-CNNs−0.7 and Co-NNs−0.7 composites have been optimized to exhibit superior ORR/OER bifunctional electrocatalytic activities. Specifically, Co-CNNs−0.7 exhibited not only a comparable half-wave potential (0.803 V vs. RHE) to that of the commercial Pt/C catalyst (0.832 V) with a larger current density for the ORR but also a lower overpotential (440 mV) toward the OER compared with the commercial IrO2 catalyst (460 mV), revealing impressive application in rechargeable ZABs. As a result, ZABs using Co-CNNs−0.7 as the cathode exhibited an excellent peak power density of 85.3 mW cm−2 with a specific capacity of 675.7 mA h g−1 and remarkable cycling stability of 1000 cycles, outperforming the commercially available Pt/C + IrO2 catalysts. This study highlights the synergy from heterointerfaces in oxygen electrocatalysis, thus providing a promising approach for advanced metal–air cathode materials.

Lithium-ion capacitors possess excellent power and energy densities, and they can combine both of those advantages from supercapacitors and lithium-ion batteries, leading to novel generation hybrid...

A three-dimensional interconnected reticular porous carbon (3D-RPC) with a large surface area of 1535 m2 g–1 by a sol–gel method followed by carbonation as well as a chemical activation process usi...

Sodium-ion capacitors (SICs) have attracted growing attention since they can combine the advantages of sodium-ion batteries (SIBs) and electrochemical capacitors simultaneously. The key point of co...

Lithium-ion capacitors (LICs) can combine the high energy density of battery-type electrode and high power density of capacitor-type electrode, which is considered as one of the most promising electrochemical storage devices. The challenge of developing superior performance LICs is designing suitable electrode materials to overcome the kinetic imbalance between the battery-type anode and the capacitor-type cathode. Herein, defect-rich carbon encapsulated Fe3C nanoparticle (Fe3C@DRC) was obtained via a modified sol-gel method with a calcination process. The defect-rich and microporous structure effectively boosts kinetics and provides additional reaction sites for lithium-ion intercalation/deintercalation process, which leads to an excellent capacity (215 mAh g−1 at 1 A g−1 after 800 cycles) and rate capability (128.8 mAh g−1 even at 10 A g−1). Then a novel Fe3C@DRC//AC LIC was consisted using Fe3C@DRC as anode and activated carbon as cathode. The Fe3C@DRC//AC LIC demonstrates a wide potential window (0–4 V), delivers a high energy density of 187.8 Wh kg−1 at a power density of 200 W kg−1, reached a high power density of 4000 W kg−1 at an energy density of 80 Wh kg−1, and coupled with a reasonable life span (84.8% after 6000 cycles at a current density of 1 A g−1). The study indicates that the introduction of defect-rich strategy may push the practical application of high-rate and high-energy LIC anode materials in energy fields.

Defect engineering is an effective way to modulate the intrinsic physicochemical properties of materials. In this work, δ-MnO2 with oxygen vacancies is fabricated by a simple oxidation or reduction process, and the relationship between the electronic structure and pseudocapacitance is systematically studied through experimental analysis and theoretical calculations. The peaks in the Raman spectra of the as-prepared samples are shifted compared with those of pure MnO2 and the Mn3+ /Mn4+ ratio and O species content also change after the introduction of oxygen vacancies. The optimized samples exhibit a better specific capacitance of 207 F g-1 after the oxidation process and 181.4 F g-1 after the reduction treatment compared with only 143.9 F g-1 for the pure MnO2 . The samples obtained through the oxidation or reduction process also retain 93.3 or 86.4 % of the initial capacity after 5000 cycles. The excellent properties are attributed to the enhanced conductivity and increased surface reactivity or electrochemically active sites. Theoretical calculations demonstrate that the presence of oxygen vacancies leads to an increase in the density of states, which improves the redox reaction of MnO2 . This study will provide a reference for exploring and designing highperformance pseudocapacitive materials.

Direct growth of hierarchically interconnected Ni3S2 nanofibers as binder-free electrodes for high-performance sodium (Na+)-ion batteries was demonstrated by a facile one-step hydrothermal method on a nickel (Ni) foam. The hierarchically interconnected Ni3S2 nanofibers can effectively relieve volume expansion of Ni3S2 and shorten diffusion paths of Na+ ions that can enhance the high electronic conductivity during the electrochemical reaction, yielding high specific capacitance, excellent cycling stability, and outstanding rate capability. As a result, a high discharge specific capacity of 584.2 mAh g–1 at a current density of 0.2 A g–1 in the first sodiation process with a capacity retention of 91.9% after 100 cycles (retains 536.9 mAh g–1) can be achieved. The asymmetric Na+-ion capacitor based on the hierarchically interconnected Ni3S2 nanofibers as binder-free anode materials and the activated carbon as a cathode material exhibits high energy and power density. Interestingly, the conversion reaction me...

Electrode materials with a favourable microstructure and morphology are greatly advantageous for the electrochemical performances of sodium ion storage devices. An excellent lamellar structure is preferable to enhance the electrochemical performance of sodium ion storage materials. In this paper, layered wrinkled WS2 nanoflakes were synthesized via a hydrothermal approach followed by a high temperature sulfidation process. Benefiting from the particular nanoflake and layered structure that can provide more reactive sites and transmission channels for sodium ions, WS2 nanoflakes exhibit outstanding electrochemical performance when applied as a sodium ion storage material. They can deliver a stable specific capacity of 170 mA h g−1 after 100 cycles at 100 mA g−1. A WS2 nanoflakes//activated carbon (AC) sodium ion capacitor (SIC) was assembled and delivered a reasonable capacity of 47.2 F g−1 at 0.1 A g−1 and a maximum energy density of 132.7 W h kg−1 at a power density of 224.9 W kg−1. The special layered structure provides a pretty good indication that the fabrication of a favourable structure can efficiently enhance the electrochemical performances of electrode materials and the superior electrochemical performances indicate the great potential of applying WS2 nanoflake materials in sodium ion storage.

Triboelectric nanogenerator (TENG) is a new energy technology, which can effectively convert ambient various mechanical energy into electricity by coupling effect of triboelectrification and electrostatic induction, yielding self-powered microelectronic devices. However, the surface charge density of triboelectric materials and the performance degradation and failure of TENG caused by wear are the key bottlenecks for its practical application. Here, we propose a high-performance and long-life TENG for harvesting wind energy that uses polyvinyl chloride/molybdenum disulfide (PVC/MoS2) composite membranes and polyamide (PA) membranes as matching triboelectric materials, and aluminum (Al) sheets with micro-nano structures as electrodes. Adding a small amount of MoS2 with excellent lubricating properties can not only effectively increase the surface charge density of composite films but also improve its wear resistance, which enhances the output performance and extends the life time of the TENG. The optimized TENG can generate an output voltage, current and maximum power up to 398 V, 40 μA and 1.23 mW, respectively, which can power tens of commercial light-emitting diodes (LEDs) and a water thermometer. Moreover, the friction coefficient of PVC after the doping of 2.5 wt % MoS2 is 0.29, which is 19.4% lower than that of pure PVC film, providing a new way to improve the surface charge density and the durability of triboelectric materials.

In this work, the RGO-modified CoWO4 nanoparticles are synthesized by a feasible hydrothermal approach and studied as the high-performance sodium-ion storage materials. RGO can effectively improve overall electrical conductivity and maintain the stability of the composite structure. The composites exhibit a stabilized reversible capacity of 160 mAh g−1 at the current density of 100 mA g−1 after 100 cycles when tested as the anode materials of sodium-ion batteries (SIBs). The sodium-ion capacitors (SICs) were assembled using CoWO4/RGO nanocomposites as the negative electrode materials and the active carbon (AC) as the positive electrode materials. It could deliver a capacitance about 31 F g−1 at the current density of 100 mA g−1 and display a specific energy of 87.2 Wh kg−1 at the power density of 224.6 W kg−1. The outstanding electrochemical properties and high energy density of CoWO4/RGO anode materials indicate the huge potential for its application to sodium-ion storage devices.

Lithium-ion capacitors possess excellent power and energy densities, and they can combine both of those advantages from supercapacitors and lithium-ion batteries, leading to novel generation hybrid devices for storing energy. This study synthesized one three-dimensional (3D) hierarchical structure, self-assembled from CoS nanosheets, according to a simple and efficient manner, and can be used as an anode for lithium ion capacitors. This CoS anode, based on a conversion-type Li

We demonstrate, for the first time, a new method of fabricating hybrid MoS2/poly(ethyleneimine)-modified graphene oxide (PEI-GO) composites assembled through electrostatically charged interaction between the negatively charged MoS2 nanosheets and positively charged PEI-GO in an aqueous solution. The GO can not only improve the electronic conductivity of the MoS2/PEI-GO composites, leading to an excellent charge-transfer network, but also hamper the restacking of MoS2 nanosheets. The composition ratios between MoS2 and PEI-GO were also optimized with the highest specific capacitance of 153.9 F g–1 where 96.0% of the initial specific capacitance remains after 6800 cycles. The specific capacitance of only 117.5 F g–1 was observed for the pure MoS2 nanosheets, and 68.2% of the initial specific capacitance was achieved after 5000 cycles. The excellent electrochemical performance of the hybrid MoS2/PEI-GO composites was demonstrated by establishing an asymmetric supercapacitor with a MoS2/PEI-GO-based negative ...

High electrical conductivity is a crucial factor for improving the electrochemical performance of energy storage materials. In the work, amorphous Ni-C nanoparticles with high electric conductivity are fabricated by mechanical alloying and are used as a novel cathode for supercapacitors. It is shown that the amorphous Ni-C retains a high specific capacitance and remarkable cycling stability after the electrode is activated by chronopotentiometry at 0.5 A g−1, and even more gratifyingly, the rate capability of the material is superior to that of other Ni based materials due to its high electrical conductivity, which is convenient for fast electron transfer in active material and fast reversible Faradic reaction characteristics. Finally, an asymmetric supercapacitor based on Ni-C as the positive electrode and activated carbon as the negative electrode could be cycled reversibly at a high working potential of 0–1.6 V and delivered a high energy density of 39.8 Wh kg−1. These results confirm the significance and tremendous potential of amorphous Ni-C materials for the development of high-performance energy supply systems.

An ion insertion type in two-dimensional (2D) materials has attracted extensive attention making 2D materials as promising energy storage materials . However, the interlayer spacing plays a key role in the design of 2D materials with fast ions de-intercalation dynamics and high-rate capability. Here, an unprecedented and convenient organic molecular welding approach was proposed to controllably tune different interlayer spacings in Ti 3C2 MXene layers, resulting in pillar and strain- xDA-Ti3C2 structures by a dehydration condensation reaction between diacid molecules (HOOC(CH2)nCOOH) and -NH2 functionalized Ti3C2 layers. The xDA molecules can not only tighten the adjacent layers acting as ropes during the ion insertion process but also pillar the adjacent layers when ion extraction process was used to stabilize the Ti3C2 structure by suppressing the volume change. Furthermore, the interlayer spacing of xDA-Ti3C2 can be controllably tuned from 1.03 to 1.45 nm by choosing xDA with different lengths and controlled interlayer spacings of 1.35 and 1.38 nm can be achieved for the best rate capability of insertion/extraction processes with the superior diffusion coefficient of 4.6 × 10−7/2.8 × 10−8 cm2/s in Li+/Na+ batteries, respectively.

Fast extraction of photo-generated charge plays a crucial function in improving the photovoltaic conversion efficiency (PCE) of the perovskite solar cells (PSCs). Here, an effective strategy to decrease the charge recombination losses by introducing versatile carbon nitride ( g-C3N4) nanosheets to the CsPbBr3 films was demonstrated. The incorporation of the g-C3N4 additive can restrain the nucleation and crystalline growth rate of perovskite films by an interaction of lone pair electrons from the exposed N atoms to the PbBr 2 precursor, resulting in high-quality CsPbBr3 films with an increase in crystalline size. Notably, a ‘coupling effect’ between the lone pair electrons from g-C3N4 nanosheets and unsaturated Pb dangling bonds (Br vacancies) around the grain boundaries significantly decreases trap states caused by defects, leading to the fewer recombination centers in CsPbBr3 films. The g-C3N4 nanosheets serving as an energy barrier can also successfully suppress the recombination loss of back electrons with holes from the g-C3N4 interface, yielding a superior PCE of 8.0% with a fill factor of 80.25%. The result opens an alternative path to enhance the performance of CsPbBr3 PSCs by passivating the trap states of perovskite films with the improvement of the crystallization quality and charge extraction efficiency.

MXenes have excellent electrochemical performance due to their remarkable electrical conductivity and abundant surface functional groups. However, the smaller interlayer spacing and self-stacking limit their practical applications. Herein, the Ba[Formula: see text] ions pillared Ti3C2 MXene (Ba[Formula: see text]–Ti3C[Formula: see text] with enlarged interlayer spacing has been successfully fabricated by electrostatic self-assembly. The pillared Ba[Formula: see text] ions between Ti3C2 layers can enlarge interlayer spacing, increase specific surface area, expose more active sites and provide open ions transfer channels due to its pillaring effects on the layered structure of Ti3C2. The Ba[Formula: see text]–Ti3C2 exhibits a higher specific capacitance (168[Formula: see text]F[Formula: see text] at 0.2[Formula: see text]A[Formula: see text] than pure Ti3C2 (123 F[Formula: see text] at 0.2[Formula: see text]A[Formula: see text]g[Formula: see text] and outstanding cycle performance, which remains at 164 F[Formula: see text] after 1100 cycles at 1[Formula: see text]A[Formula: see text]. The Ba[Formula: see text]–Ti3C2//AC asymmetric supercapacitor achieved a high power density of 1140[Formula: see text]W[Formula: see text]Kg[Formula: see text] as well as long cycle stability with capacitance retention of 86.35% at a current density of 1[Formula: see text]A[Formula: see text]g[Formula: see text] after 4000 cycles. The results demonstrate that expeading interlayer spacing can obviously enhance and optimize the supercapactive performance of MXenes, providing an idea to design the 2D energy storage materials with large interlayer spacing and high rate capability.

A facile method of chemical welding was proposed to construct the diamine molecules (xDM, x = 2, 3, 4, 6 and 8) pillared- and strained-graphene oxides (GO) with controllable interlayer spacing via the dehydration condensation reaction between GO and xDM. The interlayer spacing of xDM pillared- and strained-GO (GO-xDM) is controllably enlarged by choosing the length of xDM, which determines the pillaring effects. The GO-xDM exhibits a low diffusion barrier and ultrafast Li+ diffusion dynamics due to its enlarged interlayer spacing, which leads the excellent Li+ storage rate capability. The effects of interlayer spacing on Li+ diffusion dynamics are clarified that GO-2DM with the interlayer spacing of 0.911 nm displays the excellent Li+ storage performance and fast Li+ diffusion dynamics (DLi+=2.4 × 10−7 cm2 s−1). The GO-2DM presents a high capacity of 291.8 mAh g−1 at a current density of 0.1 A g−1 and a high-rate capability of 120.8 mAh g−1 at a current density of 5.0 A g−1. The GO-2DM//AC lithium-ion hybrid capacitor delivers a high energy density of 103.6 Wh kg−1 at a power density of 55.8 W kg−1, even reaches 2777.8 W kg−1 at a power density of 61.1 Wh kg−1. The approach of chemical welding provides a novel perspective for controllably enlarging interlayer spacing and designing two-dimensional (2D) energy storage materials with high-rate capability.

In this work, the MWO4 (M = Co, Ni) nanoparticles were successfully synthesized by a facile one-step hydrothermal method and used as novel anode materials for LIBs. The micromorphology of obtained CoWO4 and NiWO4 was uniform nanoparticles with the size of ~60 and ~40 nm, respectively, by structural characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). When tested as lithium-ion battery anode, CoWO4 nanoparticles exhibited a stabilized reversible capacity of 980 mA h g−1 at 200 mA g−1 after 120 cycles and 632 mA h g−1 at 1000 mA g−1 even after 400 cycles. And, the discharge capacity was as high as 550 mA h g−1 at the 400th cycle for NiWO4 nanoparticles. The excellent electrochemical performance could be attributed to the unique nanoparticles structure of the materials, which can not only shorten the diffusion length for electrons and lithium ions but also provide a large specific surface area for lithium storage.

Alloy materials have attracted increasing attentions because they possess superior electrical conductivity which can contribute to excellent electrochemical performance. Herein a dendritic Ni3C alloy material has been prepared by the pyrolysis of nickel acetylacetonate employing oleylamine as a reductant and 1-octadecene or octadecane as the solvent. The current–voltage curves indicating that the electrical conductivity of Ni3C is higher than that of nickel oxide. Electrochemical testing indicates that a high specific capacity of 390 C/g is found in alkaline electrolyte at 0.5 A/g, and deliver excellent rate characteristic as well as cycle life. The excellent electrochemical performance may be attributed to its high electrical conductivity and dendritic nanostructure that can promote diffusion of electrolyte ions. In addition, the AC//Ni3C asymmetric supercapacitor has been assembled at a cell voltages between 0 and 1.6 V, achieving a maximum energy density of 37 Wh/kg (at a power density of 0.3995 kW/kg), and this manifests that the Ni3C alloy is a promising electrode material for electrochemical energy storage.

The Co3O4/Co3V2O8/Ni nanocomposites were rationally designed and prepared by a two-step hydrothermal synthesis and subsequent annealing treatment. The one-dimensional (1D) Co3O4 nanowire arrays directly grew on Ni foam, whereas the 1D Co3V2O8 nanowires adhered to parts of Co3O4 nanowires. Most of the hybrid nanowires were inlayed with each other, forming a 3D hybrid nanowires network. As a result, the discharge capacity of Co3O4/Co3V2O8/Ni nanocomposites could reach 1201.8 mAh/g after 100 cycles at 100 mA/g. After 600 cycles at 1 A/g, the discharge capacity was maintained at 828.1 mAh/g. Moreover, even though the charge/discharge rates were increased to 10 A/g, it rendered reversible capacity of 491.2 mAh/g. The superior electrochemical properties of nanocomposites were probably ascribed to their unique 3D architecture and the synergistic effects of two active materials. Therefore, such Co3O4/Co3V2O8/Ni nanocomposites could potentially be used as anode materials for high-performance Li-ion batteries.

Nickel–based compounds are promising energy storage materials due to their high specific capacitance and energy density, but their practical applications are severely prevented by the poor rate capability which ascribed to the low conductivity. Herein controllable synthesis of high electrical conductive nickel phosphide alloys is achieved by conversion of Ni 3 C into Ni 2 P, Ni 7 P 3 and Ni 12 P 5 using trioctylphosphine as phosphorus source. The current-voltage curves indicating that the conductivity of these nickel phosphide alloys is higher than commercial graphite. They deliver excellent electrochemical characteristics including high specific capacitance and excellent rate capability. Simultaneously, the asymmetric supercapacitors with high energy density and long cycle life are also assembled based on nickel phosphide alloys as positive electrode and activated carbon as negative electrode. The AC//Ni 2 P asymmetric supercapacitor delivers the highest specific capacity of 239.5C g −1 at a current density of 0.5 A g −1 and a maximum energy density of 53.2 Wh kg −1 (at a power density of 0.3998 kW kg −1 ). The study will provide a new strategy for the construction of high performance energy storage materials by enhancing their intrinsic electrical conductivity and controlling their microstructure.

Transition metal phosphide alloys possess the metalloid characteristics and superior electrical conductivity and are a kind of high electrical conductive pseudocapacitive materials. Herein, high electrical conductive cobalt phosphide alloys are fabricated through a liquid phase process and a nanoparticles structure with high surface area is obtained. The highest specific capacitance of 286 F g−1 is reached at a current density of 0.5 A g−1. 63.4% of the specific capacitance is retained when the current density increased 16 times and 98.5% of the specific capacitance is maintained after 5000 cycles. The AC//CoP asymmetric supercapacitor also shows a high energy density (21.3 Wh kg−1) and excellent stability (97.8% of the specific capacitance is retained after 5000 cycles). The study provides a new strategy for the construction of high-performance energy storage materials by enhancing their intrinsic electrical conductivity.

A micro/nano flower-like Ni 3 V 2 O 8 superstructure composed of uniform two-dimensional (2D) nanoplates with thicknesses of 20–50 nm had been successfully synthesized using a facile one-step hydrothermal approach. It was found that the pH value of the mixed precursor solutions played a key role in the formation of flower-like Ni 3 V 2 O 8 structure. Importantly, the flower-like Ni 3 V 2 O 8 exhibited a high reversible capacity, good cycling stability (1047.8 mA h g −1 at 200 mA g −1 after 300 cycles), and superior rate capability (640.8 mA h g −1 at 3200 mA g −1 ) as an anode material for Li-ion batteries. Furthermore, the lithium storage mechanism of Ni 3 V 2 O 8 involving in a conversion reaction and an intercalation reaction was proposed by ex situ XRD analyses.

Co-P precursor was prepared by a mechanical alloying method and then is controlled to synthesis of CoP phase through an annealing method. The optimal conditions of ball milling and annealing temperature are investigated. The CoP exhibits higher electrical conductivity than graphite and cobalt oxide, showing excellent pseudocapacitive properties due its high electrical conductivity which can result in a fast electron transfer in high rate charge–discharge possess. The as-obtained CoP electrode achieves a high specific capacitance of 447.5 F/g at 1 A/g, and displays an excellent rate capability as well as good cycling stability. Besides, the asymmetric supercapacitor (ASC) based on the CoP as the positive electrode and activated carbon (AC) as the negative electrode was assembled and displayed a high rate capability (60% of the capacitance is retained when the current density increased from 1 A/g to 12 A/g), excellent cycling stability (96.7% of the initial capacitance is retained after 5000 cycles), and a superior specific energy of 19 Wh/kg at a power density of 350.8 W/kg. The results suggest that the CoP electrode materials have a great potential for developing high-performance electrochemical energy storage devices.

The Co 3 V 2 O 8 nanoparticle arrays on Ni foam were synthesized by a simple one-step procedure using a low-temperature hydrothermal method. This architecture consisted of ultrafine Co 3 V 2 O 8 nanoparticles with a mean size of 30–60 nm, which covered homogeneously onto the porous Ni foam, forming a uniform film-like morphology. The Co 3 V 2 O 8 nanoparticles not only provided sufficient electro-active interactions for Li-storages reaction, but also had good mechanical contact with the Ni foam, hence improving reaction kinetics and enhancing electrode integrity. When used as a new sort of binder-free anode for Li-ion batteries (LIBs), this unique electrode delivered high initial discharge capacity of 1586.9 mA h g −1 at 200 mA g −1 and retained at 1289 mA h g −1 after 100 cycles, and the discharge capacity maintained at 1004.4 mA h g −1 after 800 cycles at 500 mA g −1 . Even when the current was 10 A g −1 , discharge capacity of 471.4 mA h g −1 could be achieved. In addition, the charge/discharge mechanism of Co 3 V 2 O 8 based on conversion and intercalation reaction routes were verified by ex-situ XRD diffraction. Therefore, the Co 3 V 2 O 8 nanoparticle arrays on Ni foam might open a new insight for transition metal oxides as electrode materials for LIBs.

In this work, the MoO2/MoS2 composite material with unique flower-like microsphere structure is prepared via a facile hydrothermal synthesis. Furthermore, the composite material is served as negative electrode for supercapacitors. Ascribe to the synergistic effect, including the improved electron conductivity, the coexistence of two energy storage mechanisms, and a stable flower-like microsphere structure, the as-fabricated MoO2/MoS2 exhibits a high specific capacitance of 433.3 F g−1 at a scan rate of 5 mV s−1 and a superior cycling stability of 84.41% retention after 5000 cycles compared to that of pure MoO2 (33.33% retention after 2000 cycles) and pure MoS2 (58.33% retention after 2000 cycles) at a current density of 1 A g−1 in 1 M Na2SO4 electrolyte. Moreover, we also synthesize a series of MoO2/MoS2 electrode materials, which are used to further illustrate the synergistic effect in MoO2/MoS2 composite materials. This work signifies such materials as negative electrodes exhibit bright application prospects for supercapacitors. Keywords: Molybdenum dioxide, Molybdenum disulfide, Negative electrode, Synergistic effect, Supercapacitors