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.

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.

Interfacial Designs of MXenes for Mild Aqueous Zinc-Ion Storage.

Limited Li resources, high cost, and safety risks of using organic electrolytes have stimulated a strong motivation to develop non-Li aqueous batteries. Aqueous Zn-ion storage (ZIS) devices offer low-cost and high-safety solutions. However, their practical applications are at the moment restricted by their short cycle life arising mainly from irreversible electrochemical side reactions and processes at the interfaces. This review sums up the capability of using 2D MXenes to increase the reversibility at the interface, assist the charge transfer process, and thereby improve the performance of ZIS. First, they discuss the ZIS mechanism and irreversibility of typical electrode materials in mild aqueous electrolytes. Then, applications of MXenes in different ZIS components are highlighted, including as electrodes for Zn2+ intercalation, protective layers of Zn anode, hosts for Zn deposition, substrates, and separators. Finally, perspectives are put forward on further optimizing MXenes to improve the ZIS performance.

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.

Thickness-Independent Capacitive Performance of Holey Ti3 C2 Tx Film Prepared through a Mild Oxidation Strategy.

The Ti3 C2 Tx film with metallic conductivity and high pseudo-capacitance holds profound promise in flexible high-rate supercapacitors. However, the restacking of Ti3 C2 Tx sheets hinders ion access to thick film electrodes. Herein, a mild yet green route has been developed to partially oxidize Ti3 C2 Tx to TiO2 /Ti3 C2 Tx by introducing O2  molecules during refluxing the Ti3 C2 Tx suspension. The subsequent etching away of these TiO2  nanoparticles by HF leaves behind numerous in-plane nanopores on the Ti3 C2 Tx sheets. Electrochemical impedance spectroscopy shows that longer oxidation time of 40 min yields holey Ti3 C2 Tx (H-Ti3 C2 Tx ) with a much shorter relax time constant of 0.85 s at electrode thickness of 25 µm, which is 89 times smaller than that of the pristineTi3 C2 Tx film (75.58 s). Meanwhile, H-Ti3 C2 Tx film with 25 min oxidation exhibits less-dependent capacitive performance in film thickness range of 10-84 µm (1.63-6.41 mg cm-2 ) and maintains around 60% capacitance as the current density increases from 1 to 50 A g-1 . The findings clearly demonstrate that in-plane nanopores not only provide more electrochemically active sites, but also offer numerous pathways for rapid ion impregnation across the thick Ti3 C2 Tx film. The method reported herein would pave way for fabricating porous MXene materials toward high-rate flexible supercapacitor applications.

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.

2D Re-Based Transition Metal Chalcogenides: Progress, Challenges, and Opportunities.

The rise of 2D transition-metal dichalcogenides (TMDs) materials has enormous implications for the scientific community and beyond. Among TMDs, ReX2 (X = S, Se) has attracted significant interest regarding its unusual 1T' structure and extraordinary properties in various fields during the past 7 years. For instance, ReX2 possesses large bandgaps (ReSe2: 1.3 eV, ReS2: 1.6 eV), distinctive interlayer decoupling, and strong anisotropic properties, which endow more degree of freedom for constructing novel optoelectronic, logic circuit, and sensor devices. Moreover, facile ion intercalation, abundant active sites, together with stable 1T' structure enable them great perspective to fabricate high-performance catalysts and advanced energy storage devices. In this review, the structural features, fundamental physicochemical properties, as well as all existing applications of Re-based TMDs materials are comprehensively introduced. Especially, the emerging synthesis strategies are critically analyzed and pay particular attention is paid to its growth mechanism with probing the assembly process of domain architectures. Finally, current challenges and future opportunities regarding the controlled preparation methods, property, and application exploration of Re-based TMDs are discussed.

MoS2 nanosheets grown on hollow carbon spheres as a strong polysulfide anchor for high performance lithium sulfur batteries.

Lithium sulfur batteries are expected to be one of the most promising energy storage systems due to their high energy density, low cost and environmental friendliness. However, the shuttle effect of lithium polysulfides severely hampers their practical application. The design of the sulfur cathode is one of the most important approaches to overcome the problem. In this work, MoS2 nanosheets have been successfully grown on the surface of hollow carbon spheres (HCS) to obtain MoS2@HCS nanocomposites with uniform morphology. The growth behavior of MoS2 nanosheets was also proved by adjusting the pore structure of HCS. With a sulfur loading of 74%, the MoS2@HCS/S cathode exhibits a high initial reversible capacity of 1419 mA h g-1 at a current density of 0.1 C and remains at 1010 mA h g-1 after 100 cycles. Even at 0.5 C, a capacity of 795 mA h g-1 can be retained after 600 cycles, corresponding to a capacity retention rate of 63.1%. By adjusting the concentration of the sulfur source, the relationship between different growth quantities of MoS2 and the cycling performance of the battery was also investigated. The excellent electrochemical performance of the MoS2@HCS/S cathode can be fully attributed to its physical and chemical double adsorption effect on lithium polysulfides, which has been confirmed through the visible adsorption and X-ray Photoelectron Spectroscopy (XPS) experiments. This work provides a simple design concept and method to synthesize a nanocomposite-based sulfur host for high performance lithium sulfur batteries.

Synthesis of Ti4O7/Ti3O5 Dual-Phase Nanofibers with Coherent Interface for Oxygen Reduction Reaction Electrocatalysts.

Electrocatalysts play an important role in oxygen reduction reaction (ORR) in promoting the reaction process. Although commercial Pt/C exhibits excellent performance in ORR, the low duration, high cost, and poor methanol tolerance seriously restrict its sustainable development and application. TinO2n-1 (3 ≤ n ≤ 10) is a series of titanium sub-oxide materials with excellent electrical conductivity, electrochemical activity, and stability, which have been widely applied in the field of energy storage and catalysis. Herein, we design and synthesize Ti4O7/Ti3O5 (T4/T3) dual-phase nanofibers with excellent ORR catalytic performance through hydrothermal growth, which is followed by a precisely controlled calcination process. The H2Ti3O7 precursor with uniform size can be first obtained by optimizing the hydrothermal growth parameters. By precisely controlling the amount of reducing agent, calcination temperature, and holding time, the T4/T3 dual-phase nanofibers with uniform morphology and coherent interfaces can be obtained. The orientation relationships between T4 and T3 are confirmed to be [ 001 ] T 3 / / [ 031 ] T 4 , ( 100 ) T 3 / / ( 92 6 ¯ ) T 4 , and ( 010 ) T 3 / / ( 1 2 ¯ 6 ) T 4 , respectively, based on comprehensive transmission electron microscopy (TEM) investigations. Furthermore, such dual-phase nanofibers exhibit the onset potential and half-wave potential of 0.90 V and 0.75 V as the ORR electrocatalysts in alkaline media, respectively, which illustrates the excellent ORR catalytic performance. The rotating ring-disk electrode (RRDE) experiment confirmed the electron transfer number of 3.0 for such catalysts, which indicates a mixture of two electron and four electron transfer reaction pathways. Moreover, the methanol tolerance and cycling stability of the catalysts are also investigated accordingly.

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.