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Because of the intensified electrochemical activities, mixed metal oxides as a representative for pseudocapacitive materials play a key role for high performance supercapacitor electrodes. Nevertheless, low ion and electron transfer rate and poor cycling performance in the electrode practically restrict further promotion of their electrochemical performance. In order to offset the defect, a novel copper (Cu) foam-supported nickel molybdate nanosheet decorated carbon nanotube wrapped copper oxide nanowire array (NiMoO4 NSs-CNTs-CuO NWAs/Cu foam) flexible electrode is constructed. The as-prepared electrode demonstrates a unique core-shell holey nanostructure with a large active surface area, which can provide a large number of active sites for redox reactions. Besides, the CNTs networks supply improved conductivity, which can hasten electron transport. Through this simple and efficient design method, the spatial distribution of each component in the flexible electrode is more orderly, short and fast electron transport path with low intrinsic resistance. As a result, the NiMoO4 NSs-CNTs-CuO NWAs/Cu foam as an adhesiveless supercapacitor electrode material exhibits excellent energy storage performance with high specific areal capacitance of 23.40 F cm−2 at a current density of 2 mA cm−2, which outperforms most of the flexible electrodes reported recently. The assembled asymmetric supercapacitor demonstrates an energy density up to 96.40 mW h cm-3 and a power density up to 0.4 W cm-3 under a working voltage window of 1.7 V. In addition, outstanding flexibility of up to 100° bend and good cycling stability with the capacitance retention of 82.53 % after 10,000 cycles can be obtained.

Heat-resistant supercapacitors with excellent mechanical strength are highly required for flexible and wearable electronics in our daily life. Here, high-performance and heat-resistant solid-state ...

Due to the enhanced electrochemical activities, mixed metal oxides offer new and fascinating opportunities for high-performance supercapacitor electrodes. However, sluggish ionic and electronic kinetics within the electrode fundamentally limit further improvement of their electrochemical performance. To compensate for the deficiency, a flexible electrode (CNTF/Ni-Co-Mn-Mo NS/CNTN) composed of vertically-aligned areolate quaternary metal oxide nanosheets sandwiched between carbon nanotubes (CNTs) is constructed in this study, which demonstrates a unique hierarchical porous structure that can provide three-dimensional transport channels for both ions and electrons. The vertically aligned areolate quaternary metal oxide nanosheets enable increased exposed surface area and paths for ion transport, diffusion and redox reactions, resulting in an evident enhancement in electrochemical activities. Besides, the CNT networks provide improved conductivity, which can accelerate the electron transport. As a result, the flexible supercapacitor based on the CNTF/Ni-Co-Mn-Mo NS/CNTN electrode demonstrates a specific areal capacitance of 3738 mF cm−2, corresponding to a high energy density of 1.17 mW h cm−2, which outperforms most of the flexible devices reported recently. Additionally, excellent flexibility of up to 180° bend and superior performance stability of 87.87% capacitance retention after 10,000 charge-discharge cycles can be obtained. This unique design opens up a new way in the development of flexible energy storage devices with high performance.

The Co/N-doped carbon material, as an important electrocatalytic material, has been attracted intense interest in ORR and Zn-air battery. Here, we report an efficient Co@N-doped carbon catalyst (Co@N-C-1) obtained by pyrolysis of ZIF precursor with 2-aminobenzimidazole. The introduction of 2-aminobenzimidazole results in the formation of hierarchical meso/microporous structure of the as-prepared Co@N-C-1, effectively avoiding the aggregation of Co nanoparticles during pyrolysis and the higher N content, which contributes to enhance the ORR electrocatalytic activities. The obtained Co@N-C-1 exhibits remarkable ORR performance with a half-wave potential of 0.938 V vs RHE in alkaline media. As the air catalyst of zinc-air batteries, Co@N-C-1 displays 1.439 V of open-circuit voltage and 1413.3 Wh·kg-1 of energy density.

Generally, polyacrylonitrile (PAN)-based hydrogels possessing excellent mechanical properties are prepared by water replacement after the copolymerization of acrylonitrile (AN) and other hydrophilic monomers in their good organic solvents. However, PAN-based hydrogels synthesized by the conventional strategy not only cause huge environmental problems but also inevitably lose their pristine mechanical properties at subzero temperatures, which severely limits their real-world applications. Here, we designed a novel PAN-based hydrogel under an aqueous system containing ZnCl2 salts without any toxic organic solvents. Based on the salt used in the polymerization strategy, P(AN-co-AMPS) hydrogels (AAHs) can be realized by direct co-polymerization of AN and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) in water in the presence of ZnCl2 salts. ZnCl2 serves three predominant functions: dissolving AN in water to conduct polymerization, inhibiting the formation of ice crystals to realize freeze-tolerance under extremely cold conditions and introducing free ions to promote the conductivity of the hydrogel. Consequently, the AAH simultaneously possesses long-term stability, excellent anti-freezing properties and a high conductivity of 1.16 S m−1 even at −50 °C. Moreover, we demonstrated the AAH as a wearable strain sensor, which features outstanding performance for monitoring different daily human activities in real time. This one-step aqueous-based approach for preparing anti-freezing and conductive PAN-based hydrogels may open a new avenue for the reliable construction of high-performance flexible sensors under environmentally friendly conditions.

Metal sulfides have been extensively studied as alternative anodes for lithium-ion batteries (LIBs) due to their high specific capacity, which comes from their combined conversion and alloying/de-alloying reactions with lithium, forming Li2S and corresponding lithium alloys, respectively. However, the large volume fluctuation during cycling, low electronic/ionic conductivities of both metal sulfides and Li2S, and the electrochemical inactivity of Li2S lead to poor reversibility and stability. Here, we report a facile way to synthesize a three-dimensional carbon-coated stannous sulfide-molybdenum disulfide composite (3D SnS–MoS2@C) which is proposed to alleviate the aforementioned problems. 3D SnS–MoS2@C exhibits a highly porous structure, which enhances the contact between the electrode and the electrolyte, promotes the transport of both electrons and Li+, and buffers the volume change during cycling. MoS2 contributes to the specific capacity and catalyzes the oxidation of Li2S. The 3D SnS–MoS2@C anode demonstrates a capacity of 887.1 mA h g−1 for the first cycle at 200 mA g−1 and achieves a capacity retention of 97.1% over 200 cycles. In addition, the ternary composite exhibits a superior rate performance and cycling lifespan, achieving a gravimetric capacity of 651.2 mA h g−1 at 1000 mA g−1 after 500 cycles. The proposed facile and effective strategy could be universally applied to other metal sulfide-based electrodes.

MnO2 has received immense consideration for supercapacitors; however, its performance in energy storage is limited by its low electroconductivity and agglomeration during the charge-discharge process. This necessitates the fabrication of flexible supercapacitor with excellent electrochemical properties for application in cable-type devices. In the current study, we have fabricated a self-standing carbonized cotton yarn (CCY) and the MnO2-based electrode by using a cotton yarn derived carbon fiber as a substrate. The electrode with hierarchical porous architecture was obtained through a redox reaction between CCY and potassium permanganate (KMnO4). Field emission scanning electron microscopy showed the deposition and uniform distribution of MnO2 nanoparticles on the surface of CCY. The electrode showed excellent capacity performance and electrochemical stability. In the electrode, the combination of MnO2 nanoparticles and CCY offered enhanced kinetics, a large surface area which resulted in high energy density (16.88 μWh/cm2) and high-power density (4770 μW/cm2). Further, the fabricated electrode showed a specific area capacity of 182.94 mF/m2 at 20 mV/s. Moreover, three flexible supercapacitors were connected in series and parallel to get higher working voltage and higher capacity, respectively, which demonstrated its potential for broad-spectrum applications in flexible devices, these results demonstrate the potential of MnO2/CCY for diverse applications in the development of cable-type devices.

Flexible fiber-based supercapacitors applied in portable energy storage devices and wearable electronics have recently aroused widespread research interests. However, challenges still exist in the pursuit of facile fabrication technique for simultaneously realizing high capacitive performance and excellent mechanical stability. Here, two novel types of core-sheathed hybrid electrodes with carbon nanotube fiber (CNF) as the core and three-dimensional (3D) porous carbon nanotubes/polypyrrole (CNTs/PPy) or reduced graphene oxide (rGO) as the sheath were hierarchically constructed through one-pot electrochemical deposition. An all-solid-state asymmetric fiber-shaped supercapacitor was assembled by wrapping the gel electrolyte coated negative CNF/rGO electrode along the positive CNF/CNTs/PPy electrode. Thanks to the combination of abundant 3D pore structure and synergistic effect of different components in the fiber electrodes, the resulted supercapacitors exhibited a broadened potential window of 1.6 V, a high areal specific capacitance of 58.82 mF cm−2 and a high areal energy density of 20.91 μW h cm−2. It should be noted that 98.6% of the initial capacitance of the supercapacitor device can still be maintained after experiencing 200 reciprocating bending cycles, demonstrating outstanding mechanical stability. Moreover, the supercapacitor exhibited excellent cyclic performance, which was testified by 90% capacity retention after 10000 times of galvanostatic charge-discharge process.

The production of ammonia (NH3) in the industrial scale basically relies on the traditional technology of Haber–Bosch, which is operated under harsh conditions with high energy consumption and a hu...

An electrolyte composed of lithium difluoro(oxalate)borate (LiDFOB) as lithium salt, N-propyl-N-methylpiperidinium bis(trifuoromethansulfonyl) imide (PP13TFSI) ionic liquid and dimethylcarbonate (DMC) as co-solvent and fluoroethylene carbonate (FEC) as additive is reported in this study. It is found that the resulted ionic liquid-based electrolyte demonstrates high ionic conductivity, low polarization and high safety performance. The Li/Li1.1Ni0.25Mn0.65O2 and Li/Graphite half-cells with the electrolyte exhibit excellent electrochemical performance, retaining capacities of more than 186 mA h g−1 and 361.6 mA h g−1 after 100 cycles, respectively. Such outstanding energy storage performance is ascribed to the joint oxidative decomposition of LiDFOB and FEC, which can form stable and low impedance solid electrolyte interface (SEI) on the Li-rich cathode and graphite anode. Besides, the SEI layer can prevent transition metal dissolution, enabling excellent cycling stability for the high voltage graphite/Li1.1Ni0.25Mn0.65O2 full cell. As a result, the full cell with the ionic liquid based electrolyte maintains a discharge capacity and capacity retention of 180 mAh g−1 and 87.54% after 100 cycles at 0.5 C and 40 °C, far superior to that obtained for commercial electrolyte. All these characteristics make the electrolyte a promising candidate for safe, high performance lithium-ion battery electrolyte.

Hollow Mo2C@C core-shell nanofibers (H-Mo2C@C/NFs) have been successfully synthesized via an integrated procedure including coaxial electrospinning, oil extraction and carbonization. As an anode of lithium-ion batteries, H-Mo2C@C/NFs delivers high discharge capacity of 1176.3 mA h g−1 in the first cycle at a current density of 0.1 A g−1 and exhibits good rate capability and reversibility. The capacity can maintain at 595.1 mA h g−1 even when the current density is up to 5 A g−1. In addition, at a high current density of 1 A g−1, H-Mo2C@C/NFs also displays extraordinary long-term cycling performance with a capacity of 674.4 mA h g−1. The excellent rate performance and cycling stability result from the synergistic effect of Mo2C nanoparticles and hollow structure nanofiber matrix. Coaxial electrospinning technology can be widely extended to manufacture other metal carbide/carbon composites to achieve important energy storage and other applications.

Transition-metal oxides (TMOs) are considered as promising anode materials for lithium ion batteries. However, the poor structural stability and relatively low electronic conductivity greatly limit their application in flexible electronic devices. Herein, a 3D hierarchical high performance MnO-based flexible electrode is fabricated through vacuum-assisted layer-by-layer assembly of 1D polydopamine coated MnO2 nanowires (MnO2@PDA NWs) and 2D graphene oxide nanosheets (GO NSs), followed by a thermal reduction process. The resulting composite (MnO@C-rGO) demonstrates excellent flexibility, structure stability and manifests outstanding lithium storage performance in terms of high reversible capacity (920 mAh g−1 at 0.2 A g−1), excellent rate capability (686 mAh g−1 at 2 A g−1 and 396 mAh g−1 at 10 A g−1) and impressive cycling stability (719 mAh g−1 at 2 A g−1 without fading after 800 cycles), exceeding most of recently reported MnO-based anodes. It is proved that the freestanding flexible MnO@C-rGO anode can be successfully applied in flexible full cell, which achieves superior flexibility and maintains good electrochemical performance during mechanical deformations.

The synthesis of NH3 heavily relies on the Haber-Bosch process suffering from a large amount of CO2 emission and energy consumption. Possessing eco-friendly and sustainable characteristics, electrochemical reduction is considered as a promising candidate for artificial N2 fixation under ambient conditions, but efficient electrocatalysts are crucial for the N2 reduction reaction (NRR). In this communication, we report that perovskite La2Ti2O7 nanosheets behave as an efficient NRR electrocatalyst with excellent selectivity under ambient conditions. In 0.1 M HCl, this catalyst achieves a high NH3 yield rate of 25.15 μg h-1 mgcat.-1 with a faradaic efficiency of 4.55% at -0.55 V vs. a reversible hydrogen electrode. Notably, it also shows high electrochemical stability.

Biomass derived porous carbons are economic and attractive materials for anode electrodes in sodium-ion batteries. In this work, a novel porous carbon has been prepared through activation of longan shell, which demonstrates an interconnected hierarchical porosity comprised of macro-, meso- and micro-pores as well with a high specific surface area of 2990 m2 g−1. Benefiting from the unique pore structure and oxygen and nitrogen dual doping, a well-developed ionic and electronic conductivity is achieved. Remarkably, it exhibits an excellent cycling stability with a capacity up to 345.9 mAh g−1 at a current density of 0.1 A g−1, and maintains a capacity of 304.2 mAh g−1 even at a high current density of 5 A g−1 after 1000 cycles as anodes for sodium-ion batteries. These results indicate that the fabricated porous carbon could be a promising electrode material for sodium-ion batteries. The mechanism of such high sodium-ion storage was also discussed with the scan-rate-dependent CV curves to quantify the pseudo-capacitive contribution.

Cyclization reaction of poly(acrylonitrile-co-2-acrylamido-2-methylpropane sulfonic acid) [P(AN-co-AMPS)] copolymer during thermal oxidative stabilization (TOS) process was investigated by FTIR and two dimensional (2D) correlation analysis technique. The results showed the mechanism of cyclization reaction at different temperatures were varying. At 200 °C, the cyclization reactions generated by autocatalytic cyclization mechanism. While at higher temperatures, the cyclization reactions took place through ionic cyclization mechanism and free radical cyclization mechanism. The AMPS comonomer could reduce the heat release of cyclization reactions and improve the stability at 200 and 230 °C. At higher temperatures, the cyclization reactions were facilitated rapidly. However, the oxidation and degradation reactions were also intense, which will cause the molecular chain to break and defects in the final carbon fibers (CFs). This research has theoretical guiding significance for the optimization of heat treatment conditions for PAN copolymers used as CFs.

Advanced ionic liquid-based electrolyte is herein characterized for the application in high voltage lithium-ion batteries. The electrolyte based on N-propyl-N-methylpiperidiniumdifluoro(oxalate)borate (PP13DFOB), lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) and dimethyl carbonate (DMC) is fully characterized in terms of anodic corrosion behavior, electrochemical properties and cathode-electrolyte interphase stability. Experimental and computational results show that the preferential oxidation of PP13DFOB results in a stable and low impedance solid electrolyte interface (SEI) film on the surface of LiNi0.5Mn1.5O4 (LNMO) cathode and a passivation layer on Al foil, which suppress transition metal dissolution and Al corrosion at high voltage. As a result, the Li/LNMO and Li/graphite coin cells with ionic liquid-based electrolyte achieve excellent electrochemical performance, displaying a discharge capacity of 121.2 mAh g−1 and 369.2 mAh g−1 after 100 cycles at 0.5 C respectively and demonstrating no distinct capacitance attenuation during charge-discharge cycles.

Acrylic fiber is one of three important synthetic fibers in the world. The disposal and reuse of large number of waste acrylic fibers from fabric manufacturers or waste recovery is an urgent economic and environmental issue. Here, a porous carbon was derived from waste acrylic fibers via pre-oxidized, carbonization and KOH activation. Furthermore, we adopted melamine as nitrogen source to dope the porous carbon materials. When used as the anode of lithium ion batteries, this nitrogen-doped porous carbon shows high reversible capacity of ca. 1200 mA h g−1 after 50 cycles at 0.1 A g−1. Reversible capacities of 550 and 370 mA h g−1 are obtained at higher current densities of 1 and 5 A g−1 after 500 cycles, respectively. The outstanding electrochemical performance are a result of its large mesopore volume, high-level N-doping (especially, pyridinic-N), large quantity of edge defects, and three-dimensional hierarchical porous architecture. This paper demonstrates that the reuse of waste industrial acrylic fibers as energy storage materials is a promising method for both energy and environmental fields.

In the present work, a new strategy is proposed to simultaneously enhance the toughness and electrochemical performance of the hydrogel with conductive microgel to form microgel-reinforced double network hydrogel. In this hydrogel, the conductive microgel is cross-linked to form the first network, which can dissipate energy to improve mechanical performance and stabilize the conductive network to improve the electrochemical performance. These hydrogels show excellent mechanical properties and good conductivity. When these hydrogels are assembled to all-gel-state intrinsically flexible and stretchable supercapacitor, they deliver outstanding capacitance. The strategy put forward here can extend the application scope of the hydrogel with multifunction.

Transition-metal oxide materials have gained significant attention as high-performance anode materials for lithium ion batteries. Great advances have been achieved in the development of micro/nanostructured materials with controllable shape and tunable pore size. In this work, a facile co-precipitation approach has been developed to fabricate the Ni-NiCo2O4@ZnCo2O4 yolk-shell nano-tetrahedron composites, which significantly improve the structural stability and conductivity of the material. The Ni-NiCo2O4@ZnCo2O4 is proven to exhibit excellent cycling and rate performance for lithium ion batteries, such as the charge capacity of 1571.9 mA h g−1 after 70 cycles at 0.1 A g−1, 1097.5 mA h g−1 after 600 cycles at 1.0 A g−1. This superior electrochemical performance may attribute to the yolk-shell architecture and the Ni-doping.

The rational structure design and strong interfacial bonding are crucially desired for high performance zinc oxide (ZnO)/carbon composite electrodes. In this context, micro-nano secondary structure design and strong dopamine coating strategies are adopted for the fabrication of flower-like ZnO/carbon (ZnO@C nanoflowers) composite electrodes. The results show the ZnO@C nanoflowers (2–6 μm) are assembled by hierarchical ZnO nanosheets (∼27 nm) and continuous carbon framework. The micro-nano secondary architecture can facilitate the penetration of electrolyte, shorten lithium ions diffusion length, and hinder the aggregation of the nanosheets. Moreover, the strong chemical interaction between ZnO and coating carbon layer via C-Zn bond improves structure stability as well as the electronic conductivity. As a synergistic result, when evaluated as lithium ion batteries (LIBs) anode, the ZnO@C nanoflower electrodes show high reversible capacity of ca. 1200 mA h g−1 at 0.1 A g−1 after 80 cycles. As well as good long-cycling stability (638 and 420 mA h g−1 at 1 and 5 A g−1 after 500 cycles, respectively) and excellent rate capability. Therefore, this rational design of ZnO@C nanoflowers electrode is a promising anode for high-performance LIBs.

Iron sulfides, as promising anode materials, have been intensively studied, but still encounter problems due to their limited cycle life caused by huge volume changes. In the present work, a facile method has been presented to prepare Fe2O3 nanobiscuits followed by poly(dopamine) coating. After thermally induced sulfurization, Fe7S8@C nanobiscuits have been successfully obtained, which show high specific capacities, excellent rate capabilities and stable cycling stability as anodes for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). They exhibit high reversible capacities of 547.3 mA h g−1 after 600 cycles and 530.8 mA h g−1 after 1000 cycles at a high current density of 5 A g−1 for LIBs and SIBs, respectively. This outstanding electrochemical performance may be attributed to the stress-buffering effect owing to the biscuit-like nanostructure and conformal surface coating with carbon.

In terms of enhancing the energy storage performance of flexible MXene electrode, both heteroatom doping and introducing electroactive “spacers” are proved to be effective strategies. In this work, a facial protective hydrothermal method is explored to synthesis nitrogen doped porous MXene/TiO2 heterostructure in one pot, which enables a well preserved conductivity of porous N-doped MXene and controlled in-situ generation of uniformly dispersed electroactive TiO2 spacers. This unique hybridized structure provides a chance to integrate several physical and chemical advantages in a complementary easy way. As a result, the assembled freestanding film electrode based on the N-doped porous MXene/TiO2 heterogeneous layers demonstrates excellent energy storage performance with an outstanding specific capacitance value of 2194.33 mF cm−2 (918.69 F g−1), which outperforms most of the heteroatom-doped MXene electrodes reported previously. Besides, the film electrode delivers excellent cycling performance with a 74.39% capacitance retention after 10,000 cycles and the as fabricated flexible supercapacitor displays almost no changes on capacitive performance when subjected to mechanical deformations, indicating its excellent flexibility and stability. This work presents a simple way of modifying MXene with N doping and inserting “spacer” for enhancing the electrochemical performance, and builds up an exciting potential for applying to highly flexible and integrated energy storage devices.

A novel two-layer reinforced carbon fiber (CF), i.e., Ag nanoparticles (Ag NPs)/graphene oxide (GO) reinforced CF (named as CF/Ag/GO) was prepared by an electrochemical deposition and electrophoretic deposition (EPD) consequently. The modified fiber showed an increased interfacial shear strength (IFSS) and tensile strength. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectrometer, atomic force microscopic (AFM) and dynamic contact angle analysis (DCA) were carried out to investigate CF reinforced composites. And test results demonstrated that the presence of Ag NPs and GO sheets increased the surface roughness and surface energy of CFs significantly. IFSS of CF/epoxy and the tensile strength of CFs were increased by 86.1% and 36.8%, respectively. Ag NPs filled in the cracks in CF effectively to enhance the tensile strength, while GO sheets improved the wettability of resin on CFs and formed mechanical interlocking between CFs and epoxy resin. These Ag NPs and GO sheets worked together in a ferocious synergy on the interface of CF and epoxy to cause the enhanced mechanical properties.

It is widely accepted that the interfacial properties of carbon fiber (CF) reinforced composites tend to be weak due to the poor wettability and chemically inert surface of CF, which greatly limits the reinforcement effect of CF in composites. Here, size-controllable graphene oxide sheets (GO) were grafted on CF using Poly(oxypropylene) Diamines (D 400 ) as the bridging agent to improve the interfacial properties of CF composites. It was found that the size and content of active functional groups on GO played important roles in controlling the surface morphology of GO grafted CF. Moreover, the interfacial shear strength (IFSS) of the middle sized GO sheets grafted CF/epoxy composites reached a maximum value of 82.2 MPa, with an enhancement of 75.6% compared with untreated CF. That is to say, the strong mechanical interlocking between CF and epoxy resin and the improved wettability of resin on CF surface were responsible for the enhancement of IFSS. Instead of decaying of fiber tensile strength after treatment, the tensile strength of GO grafted CF increased from 4.73 GPa to 5.02 GPa. The reason for the enhancement may be due to that GO bridged the surface defects on CF. This hierarchical reinforcement was believed to have widely potential applications in high performance polymer matrix composites.

The emerging wire-shaped supercapacitors (WSSs) have motivated tremendous research interests in energy storage devices. However, challenges still exist in the pursuit of high-rate performance WSS. Here, a graphene fiber made from chemical vapor deposition grown laminated graphene sheet is adopted to form a WSS which exhibits an exceptional rate capability with a relaxation time constant of 1.4 ms, smallest among WSSs reported to date. Furthermore, the resulting WSS can be charged-discharged at a high scan rate of 100 V s −1 while maintaining good capacitive behavior. When the scan rate increased by 5000 times, from 20 mV s −1 to 100 V s −1 , the graphene fiber based WSS maintains 38.6% of its original capacitance. After 10,000 galvanostatic charge-discharge cycles, the specific capacitance retains over 105%, demonstrating a long cycle stability.

The exploration of reaction process plays an important role in the mechanism study of plastic hydrothermal recovery. This work investigated the procedure of the efficient heterogeneous catalytic hydrolysis of waste monomer casting polyamide in subcritical water and then proposed the depolymerization mechanism. The solid products obtained before the complete hydrolysis became less thermodynamically stable than raw polyamide material as the degree of hydrolysis increased. According to the characterization of liquid phase products, the monomer casting polyamide was depolymerized to cyclic and linear oligomers, which were further converted to the target monomer e -caprolactam by gradual chain scission. As firstly applied in the waste polyamide hydrolysis, the zeolite H-Beta was proved a promising solid catalyst which increased the degree of hydrolysis from 31% to more than 60% (300 °C, 50 min) and facilitated to produce the intermediates with specific structure due to the microporous topology. The kinetic analyses showed that compared to the formation step of oligomers, the hydrolysis of oligomers into the monomer was the critical step which could be accelerated by the zeolite H-Beta catalyst.

The growing demand on flexible all-solid-state supercapacitors has accelerated the need for fundamental understanding of their response to extreme thermal environment. In this study, supercapacitors based on freestanding films composed of randomly oriented carbon nanotubes and H 2 SO 4 -PVA gel electrolyte were fabricated. The effect of temperature on their electrochemical behaviors was systematically investigated by using cyclic voltammogram, impedance spectroscopy and galvanostatic charge-discharge measurements at temperatures between −5 °C and 55 °C. The results indicated that the capacitance of the supercapacitor was enhanced by the increase of operating temperature while the internal resistance was reduced by virtue of the acceleration of transportation/adsorption of electrolyte ions and surface modification of the electrode. For instance, when charged with the current density of 0.2 mA cm −2 , the capacitance increased by 24.3% from −5 °C to 25 °C, and by 32.6% from 25 °C to 55 °C. Operating temperatures at or below 25 °C were found to facilitate the charge-discharge reversibility and long-term cycle stability. It has also been concluded that supercapacitors based on H 2 SO 4 -PVA gel electrolyte were not suitable for long term use at temperatures higher than 40 °C due to the aging of electrolyte.

Aerogel is a kind of novel material used to create an amphiphilic surface because of its 3D network structure and functional pore feature. Amphiphilic aerogel can be used as an excellent candidate for the supporter of interface reaction. Hydrophilic domains are highly distributed on the hydrophobic surface, which is beneficial for the two phases to come in contact with each other. In the present work, an amphiphilic graphene-based aerogel (EDGA) is cross-linked by ethylenebis(nitrilodimethylene)tetraphosphonic acid. The EDGA shows high mass adsorption capacity of both oil and water recyclability. The EDGA is used as a supporter of interface reaction. First, we decorate the nanocatalyst on the hydrophilic domain of the EDGA beneficial for its amphiphilicity. Then, this nanocatalyst-loaded EDGA is used as the supporter of the interface polymerization. This kind of a catalyst shows high efficiency for C-H activation. The synthesis strategy can extend the application scope of the multifunctional graphene-based aerogel.

In this work, a MOF-derived Co-Fe oxide porous nanorod is introduced into the freestanding MXene film to produce a high-performance flexible electrode with excellent deformability and editability. The as-prepared composite film electrode demonstrates several advantages: MXene layer functions as a binder and conductive additive to coat Co-Fe oxide, which can effectively facilitate charge transfer and maintain the excellent flexibility of the film electrode. In the meantime, Co-Fe oxide can work as a spacer, thereby expanding the interlayer distance, improving the ion transmission path in the electrode. As a result, the optimal Co-Fe oxide/Ti3C2TX composite paper manifests a remarkable volumetric capacitance of 2467.6 F cm−3 in 1 M LiCl electrolyte. When assembled into a flexible symmetrical supercapacitor, an outstanding specific areal capacitance of 356.4 mF cm−2 can be obtained. Meanwhile, the flexible supercapacitor demonstrates excellent cycling performance with a high capacitance retention of 88.2% after 10 000 charge/discharge cycles, as well as stable electrochemical energy storage stability after 100 cycles of mechanical bending, indicating its great application potential in future flexible and portable energy storage equipment.

Polysulfonamide/poly(3,4-ethylenedioxythiophene) (PSA/PEDOT) conductive composite yarns were prepared by the vapor phase polymerization technique. Ferric chloride (FeCl3) was used as the oxidant initiator with five different concentration settings (20, 40, 60, 80, and 100 g/L). The effects of oxidant concentration on the chemical composition, mechanical properties, and electrical conductivity of PSA/PEDOT composite yarns were analyzed. The surface resistance and mass-specific resistance of conductive yarns were measured to investigate its conductive behavior in terms of oxidant concentration, reaction time, impregnating time, and heating temperature. The effects of the applied voltage and the yarn’s combination structures (knotted, bundled, series, and parallel) on the electrothermal properties were determined using a direct current regulated power. It was concluded that the molecular structure and chemical composition of PSA is not changed significantly with the deposition of PEDOT. The optimized deposition settings for the preparation of the PSA/PEDOT conductive composite yarns were found to be 10 min (reaction time), 60 min (impregnating time), 80℃ (heating temperature), and 80 g/L (FeCl3 concentration). Correspondingly, the mass-specific resistance of PSA/PEDOT composite yarns could be up to 0.94 Ω g cm−2. The maximum heating temperature of PSA/PEDOT conductive composite yarns during the electrical heating procedure could be increased rapidly with an increase of applied voltage and then tended to be stable. The electrothermal properties of PSA/PEDOT conductive composite yarns with different combination structures (knotted, bundled, series, and parallel) have been investigated systematically. This study presents a new way to develop conductive polymer based yarns, which can be used as fibrous sensors, connection devices in smart clothing, and for electromagnetic shielding applications.

The emergence of stretchable electronic devices has attracted intensive attention. However, most of the existing stretchable electronic devices can generally be stretched only in one specific direction and show limited specific capacitance and energy density. Here, we report a stretchable isotropic buckled carbon nanotube (CNT) film, which is used as electrodes for supercapacitors with low sheet resistance, high omnidirectional stretchability, and electro-mechanical stability under repeated stretching. After acid treatment of the CNT film followed by electrochemical deposition of polyaniline (PANI), the resulting isotropic buckled acid treated CNT@PANI electrode exhibits high specific capacitance of 1147.12 mF cm(-2) at 10 mV s(-1). The supercapacitor possesses high energy density from 31.56 to 50.98 μWh cm(-2) and corresponding power density changing from 2.294 to 28.404 mW cm(-2) at the scan rate from 10 to 200 mV s(-1). Also, the supercapacitor can sustain an omnidirectional strain of 200%, which is twice the maximum strain of biaxially stretchable supercapacitors based on CNT assemblies reported in the literature. Moreover, the capacitive performance is even enhanced to 1160.43-1230.61 mF cm(-2) during uniaxial, biaxial, and omnidirectional elongations.

In this work, we addresses the fabrication of a flexible film electrode based on 2D MXene wrapped 3D Ni-Fe oxide nanocube mixed analogous heterostructure. The resulted composite film electrode successfully inherits the merit of different building blocks: MXene layers works as binders and conductive additives that can connect cubic Ni-Fe oxide nanoparticals, facilitate the charge transfer and avoid a significant conductivity decrease in the resulting electrode. While cubic Ni-Fe oxide serves as an active spacer inside the adjacent MXene layers to increase the interlayer space, facilitate the electrolyte diffusion and enhance the electrochemical activity of the composite film. As a result, the optimized composite film manifests excellent specific capacitance of 1038.43 mF cm−2 at current density 0.5 mA cm−2. Meanwhile by assembling into all-solid-state flexible supercapacitor, an excellent specific areal capacitance of 328.35 mF cm−2 at 0.2 mA cm−2 was achieved. Additionally, the excellent energy storage performance is well maintained with a capacitance retention of 90.9% during 10,000 charging-discharging long cycles. Furthermore, a high mechanical robustness with 88.9% capacitance remained after subjected to bending at 90° for 50 cycles, suggesting great potentials for the applications in future flexible and wearable devices.

Microcapsules are attractive core-shell configurations for studies of controlled release, biomolecular sensing, artificial microbial environments, and spherical film buckling. However, the production of microcapsules with ultra-thin shells remains a challenge. Here we develop a simple and practical osmolarity-controlled swelling method for the mass production of monodisperse microcapsules with ultra-thin shells via water-in-oil-in-water (W/O/W) double-emulsion drops templating. The size and shell thickness of the double-emulsion drops are precisely tuned by changing the osmotic pressure between the inner cores and the suspending medium, indicating the practicability and effectiveness of this swelling method in tuning the shell thickness of double-emulsion drops and the resultant microcapsules. This method enables the production of microcapsules even with an ultra-thin shell less than hundreds of nanometers, which overcomes the difficulty in producing ultra-thin-shell microcapsules using the classic microfluidic emulsion technologies. In addition, the ultra-thin-shell microcapsules can maintain their intact spherical shape for up to 1 year without rupturing in our long-term observation. We believe that the osmolarity-controlled swelling method will be useful in generating ultra-thin-shell polydimethylsiloxane (PDMS) microcapsules for long-term encapsulation, and for thin film folding, buckling and rupturing investigation.

N-doped porous carbons (NPCs) prepared via carbonization of foam polymer materials and urea are promising anode materials of lithium-ion batteries (LIBs) for their low cost and high performance. Herein, polystyrene was mixed with Melanic Mc (5 wt%) and Azobisformamide (3 wt%) to prepared the precursors of porous carbon. NPCs with different N-doping levels were then obtained by the calcination of porous carbon/urea mixture with varied weight ratios. XPS and Raman characterizations illustrate that N-doping imposes negligible effects on the chemical states of N or C, but rather promotes the formation of disordered carbon and structural defects. BET measurement confirms that N-doping enlarges the surface area. The optimized NPCs with porous carbon/urea weight ratio of 1:5 exhibits high surface area of 508.3 m2·g−1 and the pore size is found to be around 3.66 nm. The capacities of NPCs achieve 600 mAh g−1 and 443 mAh g−1 over 200 cycles at 1 A g−1 and 5 A g−1 respectively. The excellent performance of NPC is ascribed to the enhanced surface area, defects and pores, providing abundant tunnels for lithium ion diffusion. Meanwhile, N-doping improves the electrical conductivity, which also enhances the rate performance. The facile synthetic route of NPCs as well as their excellent lithium storage performance shows great potential for the application in advanced lithium-ion batteries.

Flexible energy storage electronics are gaining increasing attention in recent years, but challenge still remains in obtaining fiber-shaped devices with both high specific capacitance to provide a high energy density and mechanical stretchability/flexibility to be able to integrate under extensive bending, stretching and twisting. Here, an all-in-one fiber high performance stretchable supercapacitor is constructed based on high performance bead-like NiCo2S4@carbon nanotube and Ti3C2Tx@N/O enriched carbon cloth threads electrodes. The assembled stretchable supercapacitor demonstrates a voltage output of 1.5 V and a specific areal capacitance of 559.3 mF cm−2, resulting in a high energy density of 174.78 μWh cm−2, outperforming most of previously reported stretchable fiber-shaped supercapacitors. Moreover, the high energy storage performances are well preserved under repeatedly stretching and bending. This unique design opens up a new direction in the development of stretchable fiber-shaped energy storage devices.

Zn-air batteries have received extensive attention because of their high energy density, environmental friendliness, low cost and safety. It is vital to develop cost-effective and stable electrocatalysts for oxygen reduction reaction for Zn-air batteries. Herein, Fe 3 O 4 encapsulated in porous carbon nanobowls (Fe 3 O 4 @PCN) for oxygen reduction reaction are prepared by simple soft-template approach and calcination subsequently. The optimized catalyst 4Fe 3 O 4 @PCN-800 with uniformly doped Fe 3 O 4 nanoparticles and large surface area exhibits excellent catalytic performance and long-term durability. It displays 66 mV higher half-wave potential (0.911 V) than that of 20 wt% Pt/C catalysts in 0.1 M KOH electrolyte. It also shows excellent durability, only 5 mV attenuation of halfwave potential after 10,000 potential cycles. In addition, 4Fe 3 O 4 @PCN-800 possesses better methanol resistance than Pt/C, negligible current density fluctuation in the basic electrolyte with 3 M methanol. Impressively, when being employed as a cathode catalyst in both aqueous and solid-state Zn-air batteries, 4Fe 3 O 4 @PCN-800 presents higher open-circuit voltage, higher capacity and peak power density, and more stable discharge voltage plateaus than those of Pt/C. Furthermore, the solid-state Zn-air batteries with the optimal synthesized catalyst exhibit encouraging flexibility, which have enormous potential in the application of flexible and wearable power sources.

High performance flexible asymmetric supercapacitors based on carbon cloth are continuously prepared by a quick, low-cost, simple and scalable one-step electrochemical process within minutes without any other additives. The Fe2O3 is electrochemically deposition carbon cloth for the negative electrode, while the PEDOT and MnO2 are electrochemically co-deposited on carbon cloth for positive electrode. All processes take place within 1 min, therefore, this method can be applied in a continuous preparation mode for large-scale production, which implies its application potential in the industry. This is the first report of one-step continuous prepare of the flexible electrodes for supercapacitor. In addition, as assembled supercapacitors consisting of Fe2O3@carbon cloth and MnO2-PEDOT@carbon cloth, it achieves a high operating voltage of 2 V and a high energy density of 340 μW h cm−3 at a power density of 1.212 × 105 μW cm−3. This supercapacitor also possesses excellent flexibility and stability with 95% capacitance retained even after 1000 times bending. The larger-sized supercapacitor is further tested as watchband to power an electronic watch or light 41 LEDs for minutes. The low-cost continuous preparation method with high performance endows the flexible carbon cloth various promising applications, such as flexible asymmetric supercapacitors, flexible battery, catalysts and surface treatment.

Constructing carbon-decorated complex hollow submicrostructures with well-dispersed hetero-junctions is a highly effective approach to improving the electrochemical performance of metal sulfides for supercapacitors. Here, we develop a sequential anion-exchange, annealing, and carbon nanocoating strategy for fabricating double-shelled hollow hetero-MnCo2S4/CoS1.097 spheres with carbon coating (DHMCS@C). Single-shelled hollow hetero-MnCo2S4/CoS1.097 (SHMCS) spheres are first synthesized starting from MnCo-glycolate by anion-exchange based on the Kirkendall effect, and a subsequent topotactic conversion into double-shelled hollow hetero-MnCo2S4/CoS2 (DHMCS) spheres via a novel thermally driven contraction process, and final carbon nanocoating leads to the formation of complex DHMCS@C spheres. When tested as an attractive capacitive electrode, the DHMCS@C electrode presents a high specific capacitance of 1006 F g−1 at 1 A g−1, and a good rate capability, retaining 709 F g−1 at even 15 A g−1, and outstanding cycling performance with a capacitance retention of 91.3% after 5000 cycles. A DHMCS@C//porous carbon polyhedrons (PCPHs) asymmetric supercapacitor (ASC) device delivers an energy density as high as 51.6 Wh kg−1 at a power density of 800 W kg−1, and remarkable cycling stability with a capacitance degradation of less than 8% after 5000 cycles.

Flexible energy storage electronics have gained increasing attention in recent years, but the simultaneous acquiring of high volumetric and high areal capacities as well as excellent flexibility in order to truly implement wearable and portable electronics in practice remains challenging. Here, a conductive and highly deformable freestanding all-pseudocapacitive paper electrode (Ti3 C2 Tx /MnO2 NWs) is fabricated by solution processing of hybrid inks based on Ti3 C2 Tx MXene and ultralong MnO2 nanowires. The resulting Ti3 C2 Tx /MnO2 NWs hybrid paper manifests a remarkable areal capacitance of up to 205 mF cm-2 and outstanding volumetric capacitance of 1025 F cm-3 . Both the values are highly comparable with, or in most cases much higher than those of previously reported MXene-based flexible electrodes. The excellent energy storage performance is well maintained with a capacitance retention of 98.38% during 10 000 charge-discharge cycles. In addition, the flexible supercapacitor demonstrates excellent flexibility and electrochemical stability during repeated mechanical bendings of up to 120°, suggesting great potentials for the applications in future flexible and portable electronics.

In this study, we simulated the electric field distribution of side-by-side electrospinning by using the finite element method (FEM), and studied the effects of spinneret wall thickness, spinning voltage and receiving distance on the distribution of the electrostatic field. The receiving distance was selected as a variable in the experimental, a series of PAN/PSA composite nanofiber membranes were prepared by using a self-made side by side electrospinning device. The membranes were tested by Fourier-transform infrared (FTIR), thermogravimetric analysis (TG), and scanning electron microscope (SEM). The prepared membranes were also treated by high-temperature treatment, and the change of fiber diameter and conductivity of the membrane before and after high-temperature treatment were studied. It was found that the PAN/PSA carbonized nanofibers could achieve a better performance in heat resistance and conductivity at 200 mm receiving distance.

Sodium-ion batteries (SIBs) have attracted tremendous interest and become a worldwide research hotpot owing to their low cost and abundant resources. To obtain suitable anode materials with excellent performance for SIBs, an effective and controllable strategy is presented to fabricate SnS2 nanosheets coating on nanohollow cubic CoS2 /C (CoS2 /C@SnS2 ) composites with a hollow structure using Co-metal-organic frameworks as the starting material. As anodes for SIBs, the CoS2 /C@SnS2 electrode exhibits ultralong cycle life and excellent rate performance, which can maintain a high specific capacity of 400.1 mAh g-1 even after 3500 cycles at a current density of 10 A g-1 . When used in a full-cell, it also shows enhanced sodium storage properties and delivers a high reversible capacity of 567.3 mAh g-1 after 1000 cycles at 1 A g-1 . This strategy can pave a way for preparing various metal sulfides with fascinating structure and excellent performance for the potential application in energy storage area.

The emerging fiber-shaped supercapacitors (FSSs) have motivated tremendous research interest in energy storage devices. However, challenges still exist in the pursuit of combination of excellent electrochemical performance and mechanical stretchability. Here, a core-sheath asymmetric FSS is first made by wrapping gel electrolyte coated carbon nanotube (CNT)@MnO2 core fiber with CNT@PPy composite film. Then a stretchable helical structure is formed by over-twisting the FSS. The resulted stretchable asymmetric FSS exhibits a specific capacitance of 60.435 mF cm−2 at the scan rate of 10 mV s−1 and the capacitance performance is well maintained during repeated stretching to 20% strain. Furthermore, a high energy density of 18.88 μW h cm−2 is achieved for the stretchable FSS due to its high specific capacitance and extended potential window of 1.5 V.