Strong Electronic Interaction in High-Entropy Oxide Enhances Oxygen Evolution Reaction.

High-entropy oxides are a new type of material with significant application potential. However, the lack of a universal HEO preparation method severely limits the property study and application of HEOs. Herein, we report a universal approach of spray pyrolysis for the preparation of various HEOs and study the electrocatalytic performance of HEOs toward the oxygen evolution reaction. FeCoNiMoWOx HEO exhibits an overpotential of 281 mV at 10 mA cm-2 and a Tafel slope of 34.5 mV dec-1, which are far superior to those of the corresponding medium-entropy oxide and low-entropy oxide. It is found that the high entropy of the HEO greatly strengthens the interaction between Fe and Mo/W and produces abundant oxygen vacancies (OVs) around Mo and W. This work not only provides a universal preparation method for HEOs but also deepens our understanding of OER catalytic activity of HEOs.

Wide Temperature All-Solid-State Ti3 C2 Tx Quantum Dots/L-Ti3 C2 Tx Fiber Supercapacitor with High Capacitance and Excellent Flexibility.

Ti3 C2 Tx Quantum dots (QDs)/L-Ti3 C2 Tx fiber electrode (Q3 M7 ) with high capacitance and excellent flexibility is prepared by a wet spinning method. The assembled units Ti3 C2 Tx nanosheets (NSs) with large size (denoted as L-Ti3 C2 Tx ) is obtained by natural sedimentation screen raw Ti3 AlC2 , etching, and mechanical delamination. The pillar agent Ti3 C2 Tx QDs is fabricated by an ultrasound method. Q3 M7 fiber electrode gave a specific capacitance of 1560 F cm-3 , with a capacity retention rate of 79% at 20 A cm-3 , and excellent mechanical strength of 130 Mpa. A wide temperature all-solid-state the delaminated montmorillonite (F-MMT)/Polyvinyl alcohol (PVA) dimethyl sulfoxide (DMSO) flexible hydrogel (DHGE) (F-MMT/PVA DHGE) Q3 M7 fiber supercapacitor is assembled by using Q3 M7 fiber as electrodes and F-MMT/PVA DHGE as electrolyte and separator. It showed a volume specific capacitance of 413 F cm-3 at 0.5 A cm-3 , a capacity retention of 97% after 10 000 cycles, an energy density of 36.7 mWh cm-3 at a power density of 311 mW cm-3 , and impressive capacitance and flexibility over a wide temperature range of -40 to 60 °C. This work provides an effective strategy for designing and assembling wide temperature all-solid-state fiber supercapacitors with optimal balance of capacitive performance and flexibility.

Boron Quantum Dots Pillared Ti3 C2 Tx Membrane Electrode with High Rate Performance for Supercapacitor.

A sonication-assisted liquid-phase preparation technique is developed to prepare boron quantum dots (BQDs) with a lateral size of 3 nm in a solution of NMP and NBA; it shows a direct bandgap semiconductor with a bandgap of 3 eV and a specific capacitance of 41 F g-1 . A BQDs(10)-Ti3 C2 Tx membrane electrode with excellent capacitance and high flexibility is prepared by using Ti3 C2 Tx nanosheets (NSs) as assembled units and BQDs as pillar; it gives a specific capacitance of 524 F g-1 at 1 A g-1 in 6 m H2 SO4 electrolyte, a high capacity retention of 75%, and a minimum relaxation time of 0.51 s. An all-solid-state BQDs(10)-Ti3 C2 Tx flexibility supercapacitor is assembled by using a BQDs(10)-Ti3 C2 Tx membrane as electrodes and PVA/H2 SO4 hydrogel as electrolyte; it not only shows an area specific capacitance of 552 mF cm-2 at 1.25 mA cm-2 , a retention rate of 75%, a capacity retention of 93% after 5000 cycles, and an energy density of 40.4 Wh cm-3 at a volume power density of 416 W cm-3 , but also provides superior flexibility and can be bent to different degrees, showing that the assembled BQDs(10)-Ti3 C2 Tx membrane electrode and BQDs(10)-Ti3 C2 Tx flexible supercapacitor display broad application prospects in field of portable/wearable electronic devices.

Dual-Modified Electrospun Fiber Membrane as Separator with Excellent Safety Performance and High Operating Temperature for Lithium-Ion Batteries.

Polyacrylonitrile/Boric acid/Melamine/the delaminated BN nanosheets electrospun fiber membrane (PB3N1BN) with excellent mechanical property, high thermal stability, superior flame-retardant performance, and good wettability are fabricated by electrospinning PAN/DMF/H3BO3/C3H6N6/ the delaminated BN nanosheets (BNNSs) homogeneous viscous suspension and followed by a heating treatment. BNNSs are obtained by delaminating the bulk h-BN in isopropyl alcohol (IPA) with an assistance of Polyvinylpyrrolidone (PVP). Benefiting from the cross-linked pore structure and high-temperature stability of BNNSs, PB3N1BN electrospun fiber membrane delivers high thermal dimensional stability (almost no size contraction at 200 °C), excellent mechanical property (19.1 MPa), good electrolyte wettability (contact angle about 0°), and excellent flame retardancy (minimum total heat release of 3.2 MJ m-2). Moreover, the assembled LiFePO4/PB3N1BN/Li asymmetrical battery using LiFePO4 as the cathode and Li as the anode has a high capacity (169 mAh g-1 at 0.5 C), exceptional rate capability (129 mAh g-1 at 5 C), the prominent cycling stability without obvious decay after 400 cycles, and a good discharge capacity of 152 mAh g-1 at a high temperature of 80 °C. This work offers a new structural design strategy toward separators with excellent mechanical performance, good wettability, and high thermal stability for lithium-ion batteries.

Size-Controlled Boron-Based Bifunctional Photocathodes for High-Efficiency Photo-Assisted Li-O2 Batteries.

Photo-assisted Li-O2 batteries are introduced as a promising strategy for reducing severe overpotential by directly employing photocathodes. Herein, a series of size-controlled single-element boron photocatalysts are prepared by the meticulous liquid phase thinning methods by combining probe and water bath sonication, and their bifunctional photocathodes in the photo-assisted Li-O2 batteries are systematically investigated. The boron-based Li-O2 batteries have shown incremental round-trip efficiencies as the sized reduction of boron under illumination. It is noteworthy that the completely amorphous boron nanosheets (B4 ) photocathode not only delivers an optimizing round-trip efficiency of 190% on the basis of the ultra-high discharge voltage (3.55 V) and ultra-low charge voltage (1.87 V) but also gives a high rate performance and ultralong durability with a round-trip efficiency of 133% after 100 cycles (200 h) compared with the other-sized boron photocathodes. This remarkable photoelectric performance of the B4 sample can be attracted to the synergistic effect on the suitable semiconductor property, high conductivity, and strengthened catalytic ability of boron nanosheets coated with ultrathin amorphous boron-oxides overlayer. This research can open a new avenue to facilitate the rapid development of high-efficiency photo-assisted Li-O2 batteries.

All-solid-state Ti3C2Tx neutral symmetric fiber supercapacitors with high energy density and wide temperature range.

All-solid-state Ti3C2Tx neutral symmetric fiber supercapacitors (PVA EGHG Ti3C2Tx FSCs) with high energy density and wide temperature range are constructed by using polyvinyl alcohol (PVA)-ethylene glycol hydrogel (EGHG)-sodium perchlorate (NaClO4) as electrolyte and separator, and Ti3C2Tx fiber as electrodes. Ti3C2Tx fiber is prepared using 130 mg mL-1 Ti3C2Tx nanosheet ink as an assembly unit in a coagulation bath of isopropyl alcohol (IPA) and distilled water with 5 wt% CaCl2 by a wet spinning method. The prepared Ti3C2Tx fiber exhibits a specific capacity of 385 F cm-3 and a capacitance retention of 94 % after 10,000 cycles in 1 M NaClO4 electrolyte. The assembled PVA EGHG Ti3C2Tx FSCs deliver a specific capacitance of 41 F cm-3, a volumetric energy density of 5 mWh cm-3, and a capacitance retention of 92 % after 500 times continuous bending. Furthermore, it shows good flexibility and excellent capacitance over a wide temperature range of -40 to 40 °C and maintains its electrochemical performance under varying degrees of bending. This study provides a viable strategy for designing and assembling all-solid-state neutral symmetric fiber supercapacitors with high energy density and wide temperature range.

Atomically Dispersed Fe-N4 Sites and NiFe-LDH Sub-Nanoclusters as an Excellent Air Cathode for Rechargeable Zinc-Air Batteries.

The sluggish four-electron processes of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) limit the development of rechargeable Zn-air batteries (RZABs). Highly efficient ORR/OER bifunctional electrocatalysts are therefore highly desired for the commercialization of RZABs in large scale. Herein, the Fe-N4-C (ORR active sites) and NiFe-LDH clusters (OER active sites) are successfully integrated within a NiFe-LDH/Fe,N-CB electrocatalyst. The NiFe-LDH/Fe,N-CB electrocatalyst is first prepared by the introduction of Fe-N4 into carbon black (CB), followed by the growth of NiFe-LDH clusters. The cluster nature of NiFe-LDH effectively avoids the blocking of Fe-N4-C ORR active centers and affords excellent OER activity. The NiFe-LDH/Fe,N-CB electrocatalyst thus exhibits an excellent bifunctional ORR and OER performance, with a potential gap of only 0.71 V. The NiFe-LDH/Fe,N-CB-based RZAB exhibits an open-circuit voltage of 1.565 V and a specific capacity of 731 mAh gZn-1, which is much better than the RZAB composed of Pt/C and IrO2. Particularly, the NiFe-LDH/Fe,N-CB-based RZAB displays excellent long-term charging/discharging cyclic stability and rechargeability. Even at a large charging/discharging current density (20 mA cm-2), the charging/discharging voltage gap is only ∼1.33 V and exhibits an increase smaller than 5% after 140 cycles. This work provides a new low-cost bifunctional ORR/OER electrocatalyst with high activity and superior long-term stability and will be helpful to the commercialization of RZAB in large scale.

Single-crystalline Mg-substituted Na4Mn3(PO4)2P2O7 nanoparticles as a high capacity and superior cycling cathode for sodium-ion batteries.

Mn-based mixed phosphate Na4Mn3(PO4)2(P2O7) (NMPP) is a promising cathode for high-potential, low-cost and eco-friendly sodium-ion batteries. However, this material still faces some bottleneck issues in terms of low conductivity, disturbance of impure crystalline phase, micron-sized agglomerated particles and the Mn3+ Jahn-Teller effect. Herein, a Mg-substituted NMPP (NM2.7Mg0.3PP)@C composite was constructed via modified solution combustion and subsequent calcination treatment. The obtained NM2.7Mg0.3PP presents a highly pure phase and single-crystalline characteristics. It is noteworthy that the sample shows a smaller particle size of 100-300 nm due to the Mg2+ incorporation, and the prepared NM2.7Mg0.3PP@C cathode exhibits considerable discharge capacity (119 mA h g-1), an improved rate capability and excellent long cycling stability of 1000 cycles. A series of measurements indicated that the Mg-substitution enhanced the electronic conductivity and ion diffusion rate, and effectively relieved the lattice distortion influenced by the multiphase transition from the Mn Jahn-Teller effect of the NM2.7Mg0.3PP@C cathode. In addition, NM2.7Mg0.3PP adopts an optimal 3Mg0.1-Mn1-Mn2-Mn3 crystal structure based on density functional theory (DFT) calculations and refined X-ray diffractometry results. These findings provide new insight into the design of highly stabilized and high-conductivity polyanionic cathodes for sodium-ion batteries.

Bifunctional Photoassisted Li-O2 Battery with Ultrahigh Rate-Cycling Performance Based on Siloxene Size Regulation.

Directly integrating the bifunctional photoelectrode into Li-O2 batteries has been considered an effective way to reduce the overpotential and promote electric energy saving. However, more regular investigations on various bifunctional photocatalysts have still been desired for high-performance photoassisted Li-O2 batteries. Herein, a systematic exploration of various-sized siloxene photocatalysts affected by Li-O2 batteries has been introduced. Compared with the utilization of larger-sized siloxene nanosheets (SNSs), the photoassisted Li-O2 battery with a siloxene quantum dot (SQD) photoelectrode delivers a superior round-trip efficiency of 230% based on the highest discharge potential up to 3.72 V and lowest charge potential of 1.60 V and enables the maintenance of a long-term cycling life with only 13% efficiency attenuation after 200 cycles at 0.075 mA/cm2. Furthermore, this system exhibits a record-high rate-cycling performance (162% round-trip efficiency, even at 3 mA/cm2) and a high discharge capacity of 2212 mAh/g at 1 mA/cm2. These ground-breaking performances could be attributed to the synergistic effect of the photocatalytic and electrocatalytic activities of SQD photocatalysts with the ideal conduction band/valence band values, the abundant defective sites, and the stronger O2 and lower LiO2 adsorption strengths of SQD photocatalysts. These systematic research studies highlight the significance of SQD bifunctional photocatalysts and could be extended to other photocatalysts for further high-efficiency photoelectric conversion and storage.

Synergy Effect of High-Stability of VS4 Nanorods for Sodium Ion Battery.

Sodium-ion batteries (SIBs) have attracted increasing interest as promising candidates for large-scale energy storage due to their low cost, natural abundance and similar chemical intercalation mechanism with lithium-ion batteries. However, achieving superior rate capability and long-life for SIBs remains a major challenge owing to the limitation of favorable anode materials selection. Herein, an elegant one-step solvothermal method was used to synthesize VS4 nanorods and VS4 nanorods/reduced graphene oxide (RGO) nanocomposites. The effects of ethylene carbonate/diethyl carbonate(EC/DEC), ethylene carbonate/dimethyl carbonate(EC/DMC), and tetraethylene glycol dimethyl ether (TEGDME) electrolytes on the electrochemical properties of VS4 nanorods were investigated. The VS4 nanorods electrodes exhibit high specific capacity in EC/DMC electrolytes. A theoretical calculation confirms the advance of EC/DMC electrolytes for VS4 nanorods. Significantly, the discharge capacity of VS4/RGO nanocomposites remains 100 mAh/g after 2000 cycles at a large current density of 2 A/g, indicating their excellent cycling stability. The nanocomposites can improve the electronic conductivity and reduce the Na+ diffusion energy barrier, thereby effectively improving the sodium storage performance of the hybrid material. This work offers great potential for exploring promising anode materials for electrochemical applications.

Direct growth of SnS2 nanowall photoanode for high responsivity self-powered photodetectors.

Tin sulfide (SnS2) has attracted growing attention due to its environmental friendliness, tunable band gap and potential applications for high-sensitivity photodetectors. However, the low responsivity and slow response speed severely hinder its further applications. In this work, SnS2 nanowalls have been successfully fabricated on FTO substrates by a facile hydrothermal approach. The prepared SnS2 nanowalls were used as a photoanode material for photoelectrochemical (PEC)-type photodetectors. The SnS2 based PEC-type photodetectors exhibit excellent photocurrent density (39.06 µA cm-2), responsivity (1460 µA W-1), long-term cycling stability and self-powered behavior. The responsivity of the detector is higher than that of most reported SnS2 based PEC-type photodetectors and even some SnS2 based photoconductive photodetectors. The high responsivity and self-powered behavior enable the extended potential applications of SnS2 in PEC-type photodetectors.

Few-layer Mg-deficient borophene nanosheets: I2 oxidation and ultrasonic delamination from MgB2.

By using I2 as an oxidant and CH3CN as a reaction medium, few-layer Mg-deficient borophene nanosheets (FBN) with a stoichiometric ratio of Mg0.22B2 are prepared by oxidizing MgB2 in a mixture of CH3CN and HCl for 14 days under nitrogen protection and followed by ultrasonic delaminating in CH3CN for 2 h. The prepared FBN possess a two-dimensional flake morphology, and they show a clear interference fringe with a d-spacing of 0.251 nm corresponding to the (208) plane of rhombohedral boron. While maintaining the hexagonal boron networks of MgB2, the FBN have an average thickness of about 4.14 nm (four monolayer borophene) and a lateral dimension of 500 nm, and the maximum Mg deintercalation rate can reach 78%. The acidity of the reaction system plays an important role; the HCl reaction system not only facilitates the oxidation of MgB2 by I2, but also increases the deintercalation ratio of Mg atoms. Etching of the Mg atom layer with HCl, the negative charge decrease of the boron layer by I2 oxidation, and the Mg chelating effect from CH3COOH due to the hydrolysis of CH3CN in an HCl environment led to a high deintercalation rate of the Mg atom. Density functional theory (DFT) calculations further support the result that the maximum deintercalation rate of Mg atoms is about 78% while maintaining the hexagonal layer structure of boron. This research solves the problems of low Mg atom deintercalation rate and hexagonal boron structure destruction when using the precursor MgB2 to produce borophene nanosheets, which is of great significance for large-scale novel preparation and application of borophene nanosheets.

Ultrahigh-energy sodium ion capacitors enabled by the enhanced intercalation pseudocapacitance of self-standing Ti2Nb2O9/CNF anodes.

In order to increase the capacity and improve the sluggish Na+-reaction kinetics of anodes as sodium ion capacitors (SICs), a Ti2Nb2O9/CNF self-standing film electrode comprised of Ti2Nb2O9 nanosheets and carbon nanofibers has been fabricated via electrospinning HTiNbO5 nanosheets with PAN and subsequent carbonization treatment. The as-prepared Ti2Nb2O9/CNF film electrode possesses fast Na-ion intercalation kinetics and high conductivity during Na-ion storage, and it displays a high reversible capacity of 324 mA h g-1 at 0.1 A g-1. Additionally, it also delivers a superior rate capability of 204 mA h g-1 at a high current density of 4 A g-1, as well as an excellent cycling stability of 97% retention after 2000 cycles at 1 A g-1 in a half-cell test. A prototype Ti2Nb2O9/CNF//AC SIC full device was assembled by employing the presodiated Ti2Nb2O9/CNF anode and AC cathode, and it exhibits an high energy density of 129 W h kg-1 at a power density of 75 W kg-1 and a high power density (7560 W kg-1 with 63 W h kg-1), a good cycling performance of 85% capacitance retention after 10 000 cycles at 1 A g-1, suggesting that the Ti2Nb2O9/CNF electrode with excellent performance would be a very promising candidate as the anode for high-performance SICs.

Ultra-Large Sized Siloxene Nanosheets as Bifunctional Photocatalyst for a Li-O2 Battery with Superior Round-Trip Efficiency and Extra-Long Durability.

Developing new optimized bifunctional photocatalyst is of great significant for achieving the high-performance photo-assisted Li-O2 batteries. Herein, a novel bifunctional photo-assisted Li-O2 system is constructed by using siloxene nanosheets with ultra-large size and few-layers due to its superior light harvesting, semiconductor characteristic, and low recombination rate. An ultra-low charge potential of 1.90 V and ultra-high discharge of 3.51 V have been obtained due to the introduction of this bifunctional photocatalyst into Li-O2 batteries, and these results have realized the round-trip efficiency up to 185 %. In addition, this photo-assisted Li-O2 batteries exhibits a high rate (129 % round-trip efficiency at 1 mA cm-2 ), a prolonged cycling life with 92 % efficiency retention after 100 cycles, and the highly reversible capacity of 1170 mAh g-1 at 0.75 mA cm-2 . This work will open the vigorous opportunity for high-efficiency utilization of solar energy into electric system.

A Queue-Ordered Layered Mn-Based Oxides with Al Substitution as High-Rate and High-Stabilized Cathode for Sodium-Ion Batteries.

Development of highly stabilized and reversible cathode materials has become a great challenge for sodium-ion batteries. O'3-type layered Mn-based oxides have deserved much attention as one of largely reversible-capacity cathodes featured by the resource-rich and low-toxic elements. However, the fragile slabs structure of typical layered oxides, low Mn-ion migration barriers, and Jahn-Teller distortion of Mn3+ have easily resulted in the severe degradation of cyclability and rate performances. Herein, a new queue-ordered superstructure is built up in the O'3-NaMn0.6 Al0.4 O2 cathode material. Through the light-metal Al substitution in O'3-NaMnO2 , the MnO6 and AlO6 octahedrons display the queue-ordered arrangements in the transition metal (TM) slabs. Interestingly, the presence of this superstructure can strengthen the layered structure, reduce the influence from Jahn-Teller effect, and suppress the TM-ions migrations during long-terms cycles. These characteristics results in O'3-NaMn0.6 Al0.4 O2 cathode deliver a high capacity of 160 mAh g-1 , an enhanced rate capability and the excellent cycling performance. This research strategy can provide the broaden insight for future electrode materials with high-performance sodium-ions storage.

Electrospun Nb2O5 nanorods/microporous multichannel carbon nanofiber film anode for Na+ ion capacitors with good performance.

For the disadvantages of both the slow reaction kinetics and the poor conductivity for Nb2O5 electrode materials as sodium-ion capacitors (SICs), Nb2O5 NRs/NMMCNF film electrode with good flexibility and high electrochemical property has been fabricated by electrospinning PAN/PMMA/H2Nb2O6·H2O homogeneous viscous suspension and followed by an annealing treatment, in which the precursor H2Nb2O6·H2O nanorods are obtained by grinding H2Nb2O6·H2O nanowires, and Nb2O5 nanorods are uniformly embedded in nitrogen doped microporous multichannel carbon nanofiber. Benefiting from the multichannel network structure, Nb2O5 NRs/NMMCNF film electrode delivers the fast kinetics of Na+-storage and the superior Na-ion storage performance, it delivers outstanding rate capability (101 mAh g-1 at 4 A g-1) and ultralong lifespan (91% capacity retention after 10,000 cycles at 2 A g-1). A Nb2O5 NRs/NMMCNF//AC SIC based on the Nb2O5 NRs@NMMCNF fiber film anode and the AC cathode is assembled. The energy density of the as-assembled device is as high as 91 Wh kg-1 and its maximum power density is 7499 W kg-1. This work offers a new structure design strategy toward intercalation-type metal oxide electrodes for application in SICs.

Ti3C2Tx Nanosheets/Ti3C2Tx Quantum Dots/RGO (Reduced Graphene Oxide) Fibers for an All-Solid-State Asymmetric Supercapacitor with High Volume Energy Density and Good Flexibility.

By using Ti3C2Tx quantum dots as interlayer spacers, Ti3C2Tx nanosheets/Ti3C2Tx quantum dots/RGO (reduced graphene oxide) fiber (M6M3RG1) is prepared by a wet-spinning method; it shows good capacitance and excellent flexibility. The M6M3RG1 fiber electrode possesses a novel network structure and a maximum volumetric capacitance of 542 F cm-3, and its capacitance and flexibility are affected by the amount of Ti3C2Tx quantum dots. Also, the Ti3C2Tx/PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)] fiber (M7P3) is prepared by injecting a homogeneous suspension of Ti3C2Tx nanosheets and PEDOT:PSS into a bath of 98 wt % H2SO4. The M6M3RG1 fiber is used as the positive electrode, and the M7P3 fiber is used as the negative electrode; a M6M3RG1//M7P3 asymmetric, flexible, solid-state supercapacitor is assembled in a PVA-H2SO4 gel electrolyte. The assembled device exhibits a volumetric capacitance of 53.1 F cm-3 and a good cycle stability of 96.6% after 5000 cycles. It also shows outstanding flexibility and mechanical properties; for example, the volumetric capacitance has no obvious change after the device is bent at 90° for 500 times. Moreover, its voltage window can be expanded to 1.5 V, and a maximum volumetric energy density of 16.6 mWh cm-3 can be achieved. This work will open up a new application area for new wearable energy storage devices based on the Ti3C2Tx fibers.

Few-layer and large flake size borophene: preparation with solvothermal-assisted liquid phase exfoliation.

The preparation of two-dimensional boron (B) nanosheets, especially for borophene, is still a challenge because of its unique structure and complex B-B bonds in bulk boron. In the present work, a novel preparation technology for borophene with only a few layers and large flake sizes is developed by a solvothermal-assisted liquid phase exfoliation process, consisting of ball milling-thinning, solvothermal swelling, and probe ultrasonic delamination. The exfoliation effect of the bulk B precursors is related to the surface tension and Hildebrand parameter of the selected solvents such as acetone, N,N-dimethyl formamide (DMF), acetonitrile, ethanol, and N-methyl pyrrolidone (NMP), and a relative small surface tension when using solvents is favorable for the exfoliation of bulk B. Four-layer thick borophene and an average lateral size of 5.05 µm can be obtained in acetone as the exfoliating solvent. The surface composition of the exfoliated few-layer borophene with large flake size hardly changes, while the chemical state of B changes to some extent because they are partly oxidized on the surface by contaminates before and after exfoliation. This acetone solvothermal-assisted liquid phase exfoliation technique can be used to prepare high quality borophene with large horizontal sizes, and it will provide the basis to study few-layer borophene with large sizes further.

CoNi2 S4 Nanoparticle/Carbon Nanotube Sponge Cathode with Ultrahigh Capacitance for Highly Compressible Asymmetric Supercapacitor.

Compared with other flexible energy-storage devices, the design and construction of the compressible energy-storage devices face more difficulty because they must accommodate large strain and shape deformations. In the present work, CoNi2 S4 nanoparticles/3D porous carbon nanotube (CNT) sponge cathode with highly compressible property and excellent capacitance is prepared by electrodepositing CoNi2 S4 on CNT sponge, in which CoNi2 S4 nanoparticles with size among 10-15 nm are uniformly anchored on CNT, causing the cathode to show a high compression property and gives high specific capacitance of 1530 F g-1 . Meanwhile, Fe2 O3 /CNT sponge anode with specific capacitance of 460 F g-1 in a prolonged voltage window is also prepared by electrodepositing Fe2 O3 nanosheets on CNT sponge. An asymmetric supercapacitor (CoNi2 S4 /CNT//Fe2 O3 /CNT) is assembled by using CoNi2 S4 /CNT sponge as positive electrode and Fe2 O3 /CNT sponge as negative electrode in 2 m KOH solution. It exhibits excellent energy density of up to 50 Wh kg-1 at a power density of 847 W kg-1 and excellent cycling stability at high compression. Even at a strain of 85%, about 75% of the initial capacitance is retained after 10 000 consecutive cycles. The CoNi2 S4 /CNT//Fe2 O3 /CNT device is a promising candidate for flexible energy devices due to its excellent compressibility and high energy density.

Nb2O5 Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density.

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-Nb2O5 nanoparticles/N-doped graphene hybrid anode (T-Nb2O5/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl5 at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb2O5 nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-Nb2O5/NG were improved by doping nitrogen. The T-Nb2O5/NG anode showed superior rate capability (68 mA h g-1 even at 2 A g-1) and good cycling life (106 mA h g-1 at 0.2 A g-1 for 200 cycles and 83 mA h g-1 at 1 A g-1 for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb2O5/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg-1 at a power density of 100 W kg-1 and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g-1) and showed a promising application for highly efficient energy storage systems.