Search

The lack of high‐performance electrodes is a key factor restricting the development of sodium‐ion batteries (SIBs), and usually a certain type of electrode material alone often fails to combine the merits of high capacity and good conductivity. Herein, nitrogen‐doped carbon (NC) was used as a multifunctional bridge to uniformly compound high‐capacity MoS2 nanoparticles with highly conductive Ti3C2Tx nanosheets to form Ti3C2Tx@MoS2/NC composite with flower‐like architecture. Ultrafine MoS2 nanoparticles were uniformly anchored on Ti3C2Tx nanosheets to form nanosheets primary building blocks with a sandwich‐like architecture, which not only shortens the ion transfer distance but also enlarges the layer spacing of Ti3C2Tx favoring the storage of more sodium ions as well as their transport capacity. Moreover, the flower‐like structures with abundant edges can provide an ample active sites and high pseudocapacitance behavior. As a result, flower‐like Ti3C2Tx@MoS2/NC displays a high electrochemical properties with an excellent cycling stability over 2000 cycles (81.4 % capacity retention) and preeminent rate capacity of 383 mAh g−1 at 30 A g−1. Furthermore, Ti3C2Tx@MoS2/NC‖Na3V2(PO4)3 full cell displays a capacity of 59 mAh g−1 at 0.4 A g−1 after 180 cycles. This work displays a high‐performance anode composite for SIBs and provides insight into the preparation of other composites. [ABSTRACT FROM AUTHOR]

Summary: Doping Mn element into host material is an efficient approach to enhance the specific capacitance and cycling stability of supercapacitor. In this aspect, we fabricate Co‐Mn LDHs (CMLs) hollow polyhedron generated from ZIF‐67 via a template sacrifice method. Controllable doping of Mn element with gradient contents on the effect of electrochemical performance are investigated in detail. Moreover, in order to assemble a hybrid supercapacitor with superior energy and power output, a negative electrode based on MXene/rGO/V10O24 is synthesized considering the integration of EDLC and pseudocapacitance. As expected, the asymmetric supercapacitor of CMLs‐0.53//MXene/rGO/V10O24 delivers high energy density of 44.4 Wh kg−1, maximum power density of 12 750 W kg−1 and superior cycling life (91.6% capacitance retention after cycling 10 000 cycles). The special idea on the construction of CMLs with hollow structure can offer new insight to resolve the complicated steps during preparation procedure. The results also indicated that the device based on CMLs‐0.53 and MXene/rGO/V10O24 is a good candidate in the utilization of energy storage and conversion system in the future. [ABSTRACT FROM AUTHOR]

As a recently emerging group of 2D materials, MXene has attracted extensive attention in the energy storage field in recent years owing to their outstanding features. However, the notorious issues of inevitable oxidation stability and surface‐to‐surface self‐restacking for MXene significantly prevent its further wide‐ranging application. Herein, the 3D macroporous oxidation‐resistant Ti3C2Tx MXene/graphene/carbon nanotube (MRC) hybrid hydrogels are prepared by a simple gelation method assisted by l‐cysteine as crosslinker and l‐ascorbic acid (VC) as reductant. Benefitting from the effectively alleviated restacking, excellent electrical conductivity, and the 3D inter‐crosslinked macroporous architecture, as a supercapacitor electrode, the obtained MRC aerogel exhibits a superior specific capacitance of 349 F g−1, unparalleled rate capability (52.0% at 3000 mV s−1) and amazing cyclic stability (retention of 97.1% after 100 000 cycles). Moreover, the 3D MRC‐30 aerogel exhibits an impressive oxidation‐resistant performance with just a 9.3% increase in electrical resistance after storing in ambient condition for 60 days, effectively alleviating the oxidation problem of MXene. This work demonstrates a new method for construction of 3D oxidation‐resistant MXene hydrogel, shedding new light on the promising applications of MXene materials, especially in high humidity and oxygen environment. [ABSTRACT FROM AUTHOR]

2D MXene materials have attracted intensive attention in energy storage application. However, MXene usually undergoes serious face‐to‐face restacking and inferior stability, significantly preventing its further commercial application. Herein, to suppress the oxidation and self‐restacking of MXene, an efficient and fast self‐assembly route to prepare a 3D porous oxidation‐resistant MXene/graphene (PMG) composite with the assistance of an in situ sacrificial metallic zinc template is demonstrated. The self‐assembled 3D porous architecture can effectively prevent the oxidation of MXene layers with no evident variation in electrical conductivity in air at room temperature after two months, guaranteeing outstanding electrical conductivity and abundant electrochemical active sites accessible to electrolyte ions. Consequently, the PMG‐5 electrode possesses a striking specific capacitance of 393 F g−1, superb rate performance (32.7% at 10 V s−1), and outstanding cycling stability. Furthermore, the as‐assembled asymmetric supercapacitor possesses a pronounced energy density of 50.8 Wh kg−1 and remarkable cycling stability with a 4.3% deterioration of specific capacitance after 10 000 cycles. This work paves a new avenue to solve the two long‐standing significant challenges of MXene in the future. [ABSTRACT FROM AUTHOR]

Summary: Transition metal sulfides show excellent performance in an aqueous supercapacitor. However, all‐solid‐state supercapacitors are attracting more and more interest because of thinner, lighter, and more flexible. Binary sulfides Ni3Co6S8 nanowire arrays (NCS) are directly grown on a nitrogen‐doped carbon foam (NCF) through hydrothermal reaction, which is applied as a binder‐free electrode for all‐solid‐state supercapacitor. The unique needlelike structure assembled by nanosheet effectively increases the utilization efficiency of active materials and promotes electrochemical performance. The NCS‐NCF electrode shows promising application potential for wearable electronic devices due to the flexibility of NCF. A high‐specific capacitance of 243 mAh g−1is delivered by NCS‐NCF electrode, which also exhibits good rate behavior along with outstanding cycle stability. The NCS‐NCF electrode (positive electrode) and NCF electrode (negative electrode) are employed to assemble asymmetric all‐solid‐state supercapacitor. When the high power density is 675 W kg−1, the energy density of supercapacitor reaches the maximum of 28.31 Wh kg−1. The specific capacitance of supercapacitors could maintain 84%, after 10 000 cycles of galvanostatic charge and discharge under 4 A g−1, indicating the potential application of NCS‐NCF electrode as an excellent supercapacitor electrode material in flexible, wearable energy storage systems. [ABSTRACT FROM AUTHOR]

Cobalt manganese hydroxides with well-defined nanowire morphology (CoMn-HW) is scalable fabricated by adjusting solution contents, Mn/Co ratio and alkaline species. To further improve the conductivity of CoMn-HW, GO is introduced during fabrication process and reduced to rGO according to the high temperature and alkali atmosphere. By optimizing the adding mass of rGO, CoMn-HW/rGO with sandwiched like structure is successfully synthesized for supercapacitor electrode. The composite delivers a high specific capacitance of 784 F g−1 at current density of 0.5 A g−1, good rate capability (84.2% capacitance retention after current density increase 10 times). Moreover, an asymmetric supercapacitor with CoMn-HW/rGO10 as the positive electrode and active carbon as the negative electrode, is assembled and delivers a maximum energy density of 38.3 Wh kg−1 and power density of 8000 W kg−1, representing its potential in energy storage and conversion systems. • Co, Mn-hydroxides with nanowire morphology is scalable fabricated. • CoMn-HW/rGO with sandwiched like structure is synthesized under optimal synthesis condition. • An asymmetric supercapacitor based on CoMn-HW/rGO and AC is assembled with high energy and power densities. [ABSTRACT FROM AUTHOR]

In this article, ZnCo 2 O 4 nanowires deposited with two kinds of typical layered double hydroxides (Ni–Al,Co–Al LDH) are developed via scalable method. Two materials all display core–shell hierarchical structure. High specific capacitance of 2041 F g−1 and 1586 F g−1 are obtained for ZnCo 2 O 4 @Co–Al LDH and ZnCo 2 O 4 @Ni–Al LDH,respectively. Combining with active surface and synergistic effect, the role of hierarchical structure in enhancing performance is revealed. Moreover, two all solid state supercapacitors based on fabricated materials as positive electrodes, activated carbon as negative electrodes and PVA–KOH as polymer electrolyte are assembled. The maximum power and energy densities of ZnCo 2 O 4 @Co–Al LDH//AC are 6200 W kg−1 and 50.1 Wh kg−1, respectively. While the power and energy densities of ZnCo 2 O 4 @Ni–Al LDH//AC are 3400 W kg−1 and 27.8 Wh kg−1. At last, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor ZnCo 2 O 4 @Co–Al LDH//AC as output device, is integrated as a self–sustaining power device, indicating its potential in practical applications. In this article, ZnCo 2 O 4 nanowires deposited with two kinds of typical layered double hydroxides (LDHs) are developed via scalable method. Combining with active surface and synergistic effect, the role of hierarchical structure of each material in enhancing performance is revealed. Moreover, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor as output device, is integrated as a self–sustaining power device, further indicating its potential in practical applications. Image 1 [ABSTRACT FROM AUTHOR]

Polydopamine modified reduced graphene oxides (PDA‐rGO) are synthesized by a facile dopamine polymerization reaction. As‐prepared PDA‐rGO shows a capable electrochemical performance as an electrode material for supercapacitors. A capacitance of 120 F g−1 is achieved at current density of 2 A g−1. PDA‐rGO also presents a superior cycling performance with capacitance retention of ∼99% after 10000 cycles. The remarkable electrochemical performance is attributed to the addition of PDA, which prevents the stacking of rGO and enhances the wettability of composite. Meanwhile, the rGO with high conductivity promise fast electronic transport. Polydopamine modified reduced graphene oxides (PDA‐rGO) are synthesized by a facile dopamine polymerization reaction. A capacitance of 120 F g−1 is achieved at current density of 2 A g−1. PDA‐rGO also presents a superior cycling performance with capacitance retention of ∼99% after 10000 cycles. The remarkable electrochemical performance is attributed to the addition of PDA, which prevents the stacking of rGO and enhances the wettability of composite. [ABSTRACT FROM AUTHOR]

[Display omitted] • OMC@NiO/Ni is synthesized via solvothermal reaction and subsequent calcination treatment. • "Trunk-leaf vein" structure endows OMC@NiO/Ni with superior electrochemical performance. • An asymmetric supercapacitor based on OMC@NiO/Ni and rGO/VO x as positive and negative electrodes respectively, is assembled. Supercapacitors are sustainable energy storage devices with the characteristics of high power density, long life span and ultrafast charge-discharge time. Herein, considering low conductivity of NiO and inspired by the "trunk-leaf vein" structure, mesoporous carbon and nickel dots are introduced into structure reacting as electron scaffold via facile hydrothermal and annealing procedures. Special hierarchical structure is obtained with oxygen modified mesoporous carbon (OMC) as core and NiO sheets as core accompanying with metallic nickel dots deposited on NiO sheets. Such "trunk-leaf vein" architecture can effectively ensure more active sites contacting with electrolyte, furthermore provide conductive scaffolds for electron transport. As expected, the OMC@NiO/Ni exhibits high specific capacitance of 651.3 F g−1 at 2 A g−1 and superior cycling life of 92.2% after 4000 cycles. Moreover, a novel negative electrode rGO/VO x is synthesized ascribe to the superior capacitance and life span. At last, an asymmetric device is assembled using OMC@NiO/Ni as positive electrode and rGO/VO x as negative electrode, which delivers maximum energy density of 44.3 Wh kg−1, high power density of 12,000 W kg−1 and excellent cycling life of 94.5% after 5000 cycles. The high performance of OMC@NiO/Ni renders it a potential material for energy storage-conversion equipments. [ABSTRACT FROM AUTHOR]

Highlights: A freestanding MXene-derived defect-rich TiO2@reduced graphene oxides (M-TiO2@rGO) foam electrode was fabricated. M-TiO2@rGO presents fast Na+ storage kinetics due to capacitive contribution. M-TiO2@rGO foam electrode displays a capacity retention of 90.7% after 5000 cycles. Sodium ion batteries and capacitors have demonstrated their potential applications for next-generation low-cost energy storage devices. These devices's rate ability is determined by the fast sodium ion storage behavior in electrode materials. Herein, a defective TiO2@reduced graphene oxide (M-TiO2@rGO) self-supporting foam electrode is constructed via a facile MXene decomposition and graphene oxide self-assembling process. The employment of the MXene parent phase exhibits distinctive advantages, enabling defect engineering, nanoengineering, and fluorine-doped metal oxides. As a result, the M-TiO2@rGO electrode shows a pseudocapacitance-dominated hybrid sodium storage mechanism. The pseudocapacitance-dominated process leads to high capacity, remarkable rate ability, and superior cycling performance. Significantly, an M-TiO2@rGO//Na3V2(PO4)3 sodium full cell and an M-TiO2@rGO//HPAC sodium ion capacitor are fabricated to demonstrate the promising application of M-TiO2@rGO. The sodium ion battery presents a capacity of 177.1 mAh g−1 at 500 mA g−1 and capacity retention of 74% after 200 cycles. The sodium ion capacitor delivers a maximum energy density of 101.2 Wh kg−1 and a maximum power density of 10,103.7 W kg−1. At 1.0 A g−1, it displays an energy retention of 84.7% after 10,000 cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • The composite was synthesized by a hydrothermal and vapor phase sulfidation method. • The hetrostruction and MXene improve the Na+ reaction kinetics. • The composite exhibits excellent rate and superior cycle stability. Molybdenum trioxide (MoO 3) is regarded as a promising material for rechargeable batteries attributed to its low cost, high theoretical capacity and eco-friendliness. Herein, N-doped carbon (NC) coated MoO 3 /MoS 2 composite decorated on MXene nanosheets (MoO 3 /MoS 2 /NC/MXene) has been synthesized by gas-phase vulcanization and coating of NC. The electrical conductivity and kinetics of ion diffusion/transport are greatly enhanced due to the vulcanization, NC coating and introduction of MXene. As a consequence, the composite exhibits high discharge capacity of 464 mAh/g at a current density of 0.1 A/g and still maintains a capacity of 202 mAh/g at a high current density of 5 A/g when used as the anode material for sodium-ion batteries. Furthermore, the electrode material still remains a high discharge capacity of 320 mAh/g with the capacity retention rate of nearly 100 % after 2000 cycles at a current density of 1 A/g. [ABSTRACT FROM AUTHOR]

Binary transition metal sulfides are considered to be promising electrode materials for high-performance supercapacitors because of their ultrahigh electron conductivity and superior electrochemical activity compared to the unitary transition metal sulfides. In this work, copper cobalt sulfides nanowire arrays on nickel foam with different element ratios and porosities are prepared by using a two-step hydrothermal method, and their electrochemical performance is explored. Benefited from the high electrical conductivity, rich active sites and optimized microstructure, the optimized copper cobalt sulfides (CuCo 2 S 4) electrode can achieve a ultrahigh specific capacitance of 2446.6 F·g−1 at 1 A·g−1 and favorable rate performance. The asymmetric supercapacitor assembled with the CuCo 2 S 4 nanowire array and activated carbon (AC) electrodes displays a high energy density of 33.4 Wh·kg−1 at a power density of 751.5 W·kg−1 can be obtained. Additionally, the assembled asymmetric cell shows a favorable capacitance retention of 78% after charging and discharging for 10,000 cycles at a high current density of 4 A·g−1. • The CuCo 2 S 4 electrode achieves an ultrahigh specific capacitance of 2446 F·g−1 at 1 A·g−1. • The CuCo 2 S 4 electrode has unique microstructure and exhibits good rate performance. • The CuCo 2 S 4 /AC-ASC displays high energy density of 33.4 Wh·kg−1 at power density of 751.5 W·kg−1. [ABSTRACT FROM AUTHOR]

Highlight • A two-step hydrothermal strategy is adopted to transform Ni 3 [Fe(CN) 6 ] 2 to NiFe 2 O 4. • NiFe 2 O 4 @rGO slice is prepared as electrode for flexible symmetric supercapacitor. • NiFe 2 O 4 @rGO electrode shows excellent specific capacitance and cycling stability. Abstract A high working voltage and specific capacitance are vital for flexible solid-state symmetric supercapacitor (FSSC) devices to achieve decent energy densities with high power. In this paper, we report a 1.8 V FSSC based on NiFe 2 O 4 nanocubes anchored on reduced graphene oxide (rGO) cryogel electrode. Through surface protection by a free-standing three-dimensional cross-linked network structure, NiFe 2 O 4 converted from Ni 3 [Fe(CN) 6 ] 2 inhibits the original nanocube structure. Benefiting from the synergistic effects between NiFe 2 O 4 nanocubes and graphene nanosheets, the newly synthesized NiFe 2 O 4 @rGO hybrid electrode delivers a high charge storage capacity (488 F g−1 at a constant current density of 1 A g−1), excellent rate ability and cycling performance (89.8% of the initial capacitance value after 10,000 cycles). In addition, NiFe 2 O 4 @rGO FSSC has been assembled and exhibits stable behavior at bend state, as well as high energy density of 62.5 Wh kg−1, and long cycle life (93.2% of the initial capacitance value after 6000 cycles). The proposed strategy for controlling the design and synthesis of NiFe 2 O 4 @rGO nanostructures provides promise for the development of high performance electrode in advanced energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract In this work, activated carbon tube bundles (ACTBs) with porous hollow structure are prepared using dandelion fluffs as precursors. The open-framework porous structure of the ACTBs contributes to large specific surface area and enhanced electrochemical performances. Then the ACTBs are further modified with polyaniline (PANI) using the in-situ polymerization method, the unique hollow tube structure of the ACTBs effectively increases the growth area for the PANI. The PANI modified ACTBs (PANI/ACTBs) composite exhibits an excellent rate performance due to the highly retained porous hollow tube structure, which promotes the electrolyte ions diffusion and electron transport. Meanwhile, the ACTBs and PANI/ACTBs serve as the cathode and anode electrode materials for asymmetric supercapacitor, respectively. As a result, the asymmetric supercapacitor displays a high energy density of 42 Wh kg−1 and a capable cycling stability. These results demonstrate that the PANI/ACTBs composite is a promising electrode material for the energy storage devices. Graphical abstract Image 1 Highlights • The porous structure of the ACTBs contributes to the enhancement of the specific surface area and cycling stability. • The ACTBs can solve the aggregation problem and provide more space for the volume changes of the PANI particles. • The PANI/ACTBs exhibits high capacitance and the good cycling stability due to the combined advantages of PANI and ACTBs. • The PANI/ACTBs composite exhibits high energy density of 42 Wh kg−1. [ABSTRACT FROM AUTHOR]

A simple hydrothermal route is designed to decorate NiCo 2 S 4 nanoparticles on the surface of N-doped carbon nanotubes to form a coaxial composite (NiCo 2 S 4 @NCNT). Inherited the high electrical conductivity from the NCNT and high capacitive performance of NiCo 2 S 4 , the optimized NiCo 2 S 4 @NCNT composite could significantly reduce the contact resistance and effectively increase the transfer rate of ion and electron and thus benefit for its electrochemical performance enhancement. When employed as a battery-type supercapacitor electrode, the NiCo 2 S 4 @NCNT composite exhibits a high capacitance up to 783.5 C g −1 at 1 A g −1 and as well as rate performance (74.6% retention with the current density increases from 1 to 50 A g −1 ). Coupled with activated carbon (AC) negative electrode, the as-assembled hydride supercapacitor delivers a maximum energy density of 49.75 Wh kg −1 at a power density of 774.65 W kg −1 , as well as 88.9% capacitance retained after 3000 cycles at a current density of 10 A g −1 . These above results demonstrate the enormous potential of NiCo 2 S 4 @NCNT in the development of hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

A unique nanostructure electrode consisting of RuO 2 nanoparticles with ultra-fine diameter (1.9 nm) anchored on the surface of graphene nanosheets (GNS) and carbon nanotube (CNT) is prepared as a binder-free supercapacitor electrode through two-step electrochemical routes. At first, free-standing GNS and CNT (GC) are directly deposited on the surface of carbon fiber cloth (CFC) to form a cross-linked composite via a cathodic electrophoretic deposition method. Safranin, a kind of cationic organic dye, is introduced in this stage as a new-type dispersant to disperse GNS and CNT in water to form a suspension solution. After the following electro-deposition process, the as-prepared GC composite is uniform covered with RuO 2 nanoparticles. Benefiting from the combined advantages of GNS, CNT and ultra-fine RuO 2 nanoparticles in such a binder-free structure, the hybrid electrode exhibits a high specific capacitance up to 480.3 F g −1 (based on the total mass of GNS, CNT and RuO 2 ) and remarkable cycling stability (89.4% capacitance retention after 10000 cycles). Furthermore, the assembled symmetric supercapacitor exhibits a high energy density of 30.9 Wh kg −1 and power density of 14000 W kg −1 with excellent stability performance (92.7% capacitance retention after 10000 cycles). Thus, the remarkable performance of the resultant RuO 2 electrode has provided a rational design strategy for developing supercapacitors with high energy density. [ABSTRACT FROM AUTHOR]

Designing and fabricating self-supported and binder-free MnO 2 nanostructure electrode to overcome their low conductivity for supercapacitor application with high comprehensive electrochemical performance, such as high capacitance, excellent stability, and good rate capability, is still a tremendous challenge. In this paper, carbon nanotubes are uniform covered on nickel foam (denote as CNT/Ni) by a simple dip & dry method to form a 3D skeleton for MnO 2 nanosheets deposition (denoted as MnO 2 -CNT/Ni). Results show the MnO 2 -CNT/Ni electrode exhibits a unique 3D porous interconnected network with a high specific capacitance of 402.5 F g − 1 at 1 A g − 1 and a favorable cycling performance that 83% capacitance retained after 5000 cycles at a current density of 2 A g − 1 . Meanwhile, the MnO 2 -CNT/Ni//CNT/Ni asymmetric supercapacitor exhibits an excellent energy density of 25 Wh kg − 1 at a power density of 0.9 kW kg − 1 with 85.3% capacitance retention after 5000 cycles. Therefore, such a facile and manageable method to prepare MnO 2 electrode with high supercapacitor performance is offering a promising future for practical applications. [ABSTRACT FROM AUTHOR]

Herein, Polypyrrole was used as the conductive wrapping material electro-deposited on the MnO 2 nanoflakes covered on C/TiO 2 nanowire arrays to form PPy@MnO 2 @C/TiO 2 double shell/core structured arrays electrode for supercapacitor. Their structure and surface morphology were studied by using X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy. The results suggest that a thin layer of PPy was successfully wrapped on the surface of MnO 2 , and the shell/core structure of MnO 2 @C/TiO 2 nanowire arrays was not changed after electro-deposition of PPy. The electrochemical tests indicate that the PPy@MnO 2 @C/TiO 2 double shell/core arrays electrode exhibits high specific capacitance of 715 F g −1 at a charge/discharge current density of 1 A g −1 and improved specific capacitance retention to 84.0% after 1000 cycles. These results show that the unique three dimensional (3D) double shell/core structured electrode holds promise for high-performance energy storage devices. The superior capacitive perfomance may due to the unique 3D C/TiO 2 nanowires and the unique double shell/core structures. Firstly, the 3D C/TiO 2 nanowire arrays, as excellent platform for loading active materials, can facilitate the permeation of electrolyte. Moreover, the thin layer PPy tightly wrapped on the MnO 2 nanoflakes can improve the electrical conductivity of MnO 2 . Therefore, the PPy@MnO 2 @C/TiO 2 electrode is promising candidate for electrochemical energy applications. [ABSTRACT FROM AUTHOR]

In this paper, freestanding one-dimensional MnO 2 nanoflakes are successful prepared through a simple hydrothermal reaction by using the carbon shell of TiC/C core/shell arrays as the sacrificial template. Its structure and morphology are characterized by X-ray diffractometer, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectrometer and transmission electron microscopy. Results show that the thickness of the carbon shell decreased but also remained and the ultrathin MnO 2 nanoflakes with thickness less than 5 nm uniformly grow on the surfaces of the TiC/C nanowire to form a core/double shell structure after the hydrothermal reaction. The electrochemical performance of the as-prepared electrode is evaluated by cyclic voltammetrys, galvanostatic charging-discharging tests and electrochemical impedance spectroscopy, and high capacities, excellent rate capabilities and exemplary cycling performance is obtained. The as-prepared electrode shows a high specific capacitance of 598.8 F g −1 and 85.8% of its initial capacitance is retained after 10,000 cycles at a high discharge current density of 10 A g −1 , suggesting that this structure has a promising future as high-performance supercapacitor electrode. [ABSTRACT FROM AUTHOR]

• α-MnSe Nanosheets are prepared via a facile hydrothermal method. • The effect of reaction time on electrochemical performance is investigated. • The α-MnSe electrode delivers a high capacity of 88.3 mAh g−1 at 1 A g−1. • The asymmetric supercapacitor exhibits a high energy density of 39.3 Wh kg−1. Transition metal selenides are regarded as emerging materials for energy storage devices because of their good electrical conductivity and electrochemical activity. Here, a binder-free ultrathin α-MnSe nanosheets electrode is prepared and the supercapacitor performance is comprehensively explored. Due to the increased active sites, enlarged contact area for electrolyte, as well as shorten ions diffusion pathway, the prepared electrode delivers high capacity of 88.3 mAh g−1 at 1 A g−1, good rate capability, and long-term durability (91% remain after 5000 cycles). Moreover, the asymmetric supercapacitor, fabricated by α-MnSe anode and active carbon cathode, displays a high energy density of 39.3 Wh kg−1 at a power density of 0.92 kW kg−1 and satisfying cycle performance. This study demonstrates that the binder-free α-MnSe electrode holds great promise for supercapacitor. [ABSTRACT FROM AUTHOR]

Developing novel materials with rational structures and excellent electrical conductivity is vitally important for energy storage devices. Herein, hollow cobalt molybdenum selenide (Co–Mo–Se) nanosheet arrays are fabricated via a self-sacrificing template method and selenization process, where cobalt-organic framework serves as the template. Benefiting from unique hollow nanoarrays structure, the Co–Mo–Se electrode offers rich electroactive sites, large accessible regions for electrolyte, and short ions diffusion pathways. Additionally, it is observed that the Co–Mo–Se possesses a low charge transfer resistance owing to the intrinsic metallicity. As a result, the Co–Mo–Se electrode exhibits favorable energy storage properties, including high capacity (221.7 mAh g−1), good rate property, and outstanding stability (95% after 8000 cycles). More importantly, the assembled Co–Mo–Se//active carbon (AC) achieves high energy density (44.7 Wh kg−1) and remarkable durability. Notably, two hybrid devices connected in series successfully power an electronic watch for 70 min, demonstrating its practical applicability. These results indicate that the synthesized hollow Co–Mo–Se nanosheet arrays have promising applications as electrode materials for high-performance energy storage devices. • Co-MOF was employed as template to obtain hollow Co–Mo–Se nanosheet arrays. • The Co–Mo–Se delivers a specific capacity of 221.7 mAh g−1 at 1 A g−1. • The ion exchange/etching method was applied in this work. • The asymmetric supercapacitor delivers high energy and power densities. [ABSTRACT FROM AUTHOR]

• CoSe 2 /RGO composite were prepared via a facile microwave assisted method. • The effects of RGO content on electrochemical performance were investigated. • The CoSe 2 /RGO-3 electrode delivers high capacitance of 761 F g−1 at 1 A g−1. • The CoSe 2 /RGO-3//AC exhibits high energy density of 43.1 Wh kg−1 at 800 W kg−1. The composites composed of metal selenides and carbonaceous materials have revealed enormous potential in varied applications. Herein, CoSe 2 /reduced graphene oxide (CoSe 2 /RGO) composites are prepared by a low-cost and efficient microwave assisted method. The effects of RGO proportion on crystalline structure, microstructure and energy storage capacity are explored. Benefiting from the good electrical conductivity and reasonable RGO content, the CoSe 2 /RGO sample with 35.2 wt% RGO reveals an excellent specific capacitance of 761 F g−1 as well as outstanding durability. More importantly, we construct an all solid-state hybrid supercapacitor (CoSe 2 /RGO//active carbon) to broaden the voltage window, resulting in an enhanced energy density (43.1 Wh kg−1). The hybrid device presents a favorable durability with 10% capacity drop after 10,000 cycles. In addition, the practical applicability of asymmetric device is confirmed by powering a blue light emitting diode (LED) for more than 10 mins. This work presents a simple, effective, and reasonable construct strategy to synthesize composites of selenides and RGO for charge storage application. [ABSTRACT FROM AUTHOR]

Bimetallic metal selenides have gained increasing attention as potential electrode materials for energy storage systems owing to good electrical conductivity and superior electrochemical activity. Herein, the Ni x Co y Se 2 (x+y=1) electrodes are prepared by a facile and rapid electrodeposition process. The electrochemical performance is optimized via adjusting the ratio of Co and Ni. It is turned out that equivalent Co and Ni in the composite (Ni 1/2 Co 1/2 Se 2) shows the best supercapacitor performance, including high specific capacity (166.1 mAh g−1) and long-term stability. Moreover, Density Functional Theory (DFT) calculation confirms the covalent interaction between nickel and cobalt, implying the existence of synergistic effect. To assess the practical value of the rationally designed Ni 1/2 Co 1/2 Se 2 electrode material, an asymmetric supercapacitor device is fabricated (Ni 1/2 Co 1/2 Se 2 //AC), which delivers a high energy density of 46.0 Wh kg−1 at 1141 W kg−1, coupled with 9.8% capacity loss after 10000 cycles. Notably, the low-voltage setups (LED and electric fan) can be easily activated by two devices in series, further demonstrating the great potential for practical application of Ni 1/2 Co 1/2 Se 2 electrode. [ABSTRACT FROM AUTHOR]

• Bimetallic (Ni,Mo)S 2 was synthesized through a two-step solvothermal approach. • The (Ni,Mo)S 2 /G composite exhibits high specific capacity of 951 C g−1. • The ASC device shows a ultrahigh energy density of 84.5 Wh kg−1. Thanks to their high electrical conductivity, electrochemical stability and activity, transition metal sulfides have been widely designed and developed for supercapacitors with excellent electrochemical performances. Herein, we report the NiS 2 /MoS 2 mixed phases with abundant exposed active edge sites decorated on graphene nanosheets (named as (Ni,Mo)S 2 /G) through a facile two-step hydrothermal approach. Benefitting from its unique chemical property and structure, the as-prepared (Ni,Mo)S 2 /G composite possesses impressive electrochemical performances as electrodes of battery-type supercapacitors in 2 M KOH, such as high specific capacity of 951 C g−1 (2379 F g−1) at 1 A g−1 with superb rate capability (60.7% at 100 A g−1). Additionally, the asymmetric supercapacitor (ASC) device assembled based on the active edge site-enriched (Ni,Mo)S 2 /G as positive electrode and nitrogen-doped porous graphene as negative electrode displays an ultrahigh energy density of 84.5 Wh kg−1, superior to those of the Ni- and Mo-based ASCs in aqueous electrolytes reported so far. Such novel strategy may hold great promise for exploring other polymetallic sulfides with abundant exposed active edge sites for energy storage and conversion. [ABSTRACT FROM AUTHOR]

• Ultrathin in-plane 1T-2H MoS 2 heterostructures are coaxially arrayed on 3D CFs. • The 1T-2H ultrathin heterostructures exhibit surprising structure stability. • Our ASC device exhibits an ultrahigh energy density of 81.4 Wh kg−1. Metallic 1T MoS 2 is a promising anode candidate for supercapacitors due to its intrinsically excellent electrical conductivity and high electrochemical activity. However, it is quite unstable and hard to be massively synthesized through common methods. Herein, structurally stable ultrathin (1–3 layers) in-plane 1T-2H MoS 2 heterostructures have been rationally modulated and coaxially aligned on three-dimensional carbon nanofibers (MoS 2 /CF) through a facile hydrothermal approach for supercapacitors and electrocatalysis. Benefiting from the unique heterostructure, the MoS 2 /CF composite shows amazing stability with no obvious change after being stored in air for over 36 months. In addition, it presents high specific capacitance of 310 F g−1 and remarkable rate capability of 78% at 100 mV s−1. The fabricated asymmetric supercapacitor delivers an impressive energy density of 81.4 Wh kg−‍‍‍‍‍1 in 1 M Na 2 SO 4 solution attributed to the high specific capacitance and large operating voltage range of 2 V. Moreover, the MoS 2 /CF composite also demonstrates enhanced electrocatalytic activity for hydrogen evolution reaction with a low overpotential of 194 mV at 10 mA cm−2. The work may promote the developments of high-performance bifunctional energy conversion and storage systems in future. [ABSTRACT FROM AUTHOR]

• The human hair with high elasticity capable can serve as a promising flexible supporter for the electrode. • The reduced graphene oxide nanosheets can effectively improve the electrical conductivity of the electrode. • The Ni(OH) 2 nanoribbon-intercalated rGO nanosheets shows an interconnected porous structure. • The solid-state flexible supercapacitor delivers high energy density and good cycling stability. The demands for wearable energy storage devices keep growing and novel flexible electrode materials and facile prepared methods for these devices are crucial and attractive. In this work, human hair fiber is employed as the flexible fiber-based material due to the high utilization values of low cost, controllable length and high elasticity capable. Herein, an effective and hazard-free microwave-assisted method is reported to develop superelastic reduced graphene oxide coating human hair (rGO@Hh) to achieve conductive and high-strength fibrous electrode. With the braided rGO@Hh fibers, nickel hydroxide nanoribbon-intercalated rGO nanosheets (Ni(OH) 2 /rGO@Hh) are further prepared through microwave radiation treatment, which shows an interconnected porous structure with outstanding electrochemical performances of high specific capacitance (316 F g−1 at 1 A g−1) and good cycling performance. Moreover, a solid-state fiber-based asymmetric supercapacitor (FASC) is assembled with rGO@Hh fibers and Ni(OH) 2 /rGO@Hh fibers as negative and positive electrodes, which demonstrates a high energy of 27.6 Wh kg−1 and a power density of 699 W kg−1, respectively. The FASC also can be further used for numerous electronic products, presenting its prospect for portable wearable devices with high tensile strength and excellent performances. [ABSTRACT FROM AUTHOR]