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Transition metal chalcogenides especially Fe-based selenides for sodium storage have the advantages of high electric conductivity, low cost, abundant active sites, and high theoretical capacity. Herein, we proposed a facile synthesis of Fe7Se8 embedded in carbon nanofibers (denoted as Fe7Se8-NCFs). The Fe7Se8-NCFs with a 1D electron transfer network can facilitate Na+ transportation to ensure fast reaction kinetics. Moreover, Fe7Se8 encapsulated in carbon nanofibers, Fe7Se8-NCFs, can effectively adapt the volume variation to keep structural integrity during a continuous Na+ insertion and extraction process. As a result, Fe7Se8-NCFs present improved rate performance and remarkable cycling stability for sodium storage. The Fe7Se8-NCFs exhibit practical feasibility with a reasonable specific capacity of 109 mA h g−1 after 200 cycles and a favorable rate capability of 136 mA h g−1 at a high rate of 2 A g−1 when coupled with Na3V2(PO4)3 to assemble full sodium ion batteries.

Li is attractive anode for next-generation high-energy batteries. The high chemical activity, dendrite growth, and huge volume fluctuation of Li hinder its practical application. In this work, a Li-BiOF composite anode (LBOF) is obtained by combining Li metal with BiOF nanoplates through facile folding and mechanical cold rolling. Further, Li

It is a great challenge to prepare non-noble metal electrocatalysts toward hydrogen evolution reaction (HER) with large current density. Synergistic electronic and morphological structures of the catalyst have been considered as an effective method to improve the catalytic performance, due to the enhanced intrinsic activity and enlarged accessible active sites. Herein, we present novel ternary Co1−xVxP nano-needle arrays with modulated electronic and morphological structures as an electrocatalyst for highly efficient HER in alkaline solution. The NF@Co1−xVxP catalyst shows a remarkable catalytic ability with low overpotentials of 46 and 226 mV at current densities of 10 and 400 mA cm−2, respectively, as well as a small Tafel slope and superior stability. Combining the experimental and computational study, the excellent catalytic performance was attributed to the improved physical and chemical properties (conductivity and surface activity), large active surface area, and fast reaction kinetics. Furthermore, the assembled Co-V based electrolyzer (NF@Co1−xVx-HNNs(+)||NF@Co1−xVxP(−)) delivers small full-cell voltages of 1.58, 1.75, and 1.92 V at 10, 100, and 300 mA cm−2, respectively. Our findings provide a systematic understanding on the V-incorporation strategy to promote highly efficient ternary electrocatalysts via synergistic control of morphology and electronic structures.

Co9S8 is a potential anode material for its high sodium storage performance, easy accessibility, and thermostability. However, the volume expansion is a great hindrance to its development. Herein, a composite containing Co9S8 nanofibers and hollow Co9S8 nanospheres with N, S co-doped carbon layer (Co9S8@NSC) is successfully synthesized through a facile solvothermal process and a high-temperature carbonization. Ascribed to the carbon coating and the large specific surface area, severe volume stress can be effectively alleviated. In particular, with N and S heteroatoms introduced into the carbon layer, which is conducive to the Na+ adsorption and diffusion on the carbon surface, Co9S8@NSC can perform more capacitive sodium storage mechanism. As a result, the electrode can exhibit a favorable reversible capacity of 226 mA h g−1 at 5 A g−1 and a favorable capacity retention of 83.1% at 1 A g−1 after 800 cycles. The unique design provides an innovative thought for enhancing the sodium storage performance.

With the increasing demand for portable electronic devices, high-capacity supercapacitors have been widely concerned as excellent energy storage devices. Herein, ternary cobalt and copper sulfides (Co-Cu-S) are electrodeposited on the carbon cloth (CC@Ni-Co-P@Co-Cu-S), which is modified by honeycomb-like cobalt and nickel phosphates (Co-Ni-P). The modification of honeycomb-like Ni-Co-P can provide a sufficient active site for the deposition of Co-Cu-S and realize high utilization of Co-Cu-S. Thus, the specific capacity of the supercapacitor is greatly improved. The specific capacity of CC@Co-Ni-P @Co-Cu-S is 0.85 F cm−2, quintupling that of CC@Co-Cu-S, and the capacity remains 94.3% after 100 cycles. In addition, CC@Co-Ni-P@Co-Cu-S has the best electrochemical performance when Co-Cu-S was deposited for eight cycles. This study fully demonstrates that Co-Ni-P modification greatly improves the specific capacity of the CC@Co-Cu-S electrode.

The sodium storage performance of Ge-based materials suffers from poor cycling stability caused by the volume variation and collapse of the structure during cycling process. In this work, Cu3Ge coated by nitrogen-doped carbon (Cu3Ge-NC) nanorods are prepared by annealing the mixture of CuGeO3 nanowires and polyacrylonitrile which acts as nitrogen and carbon source. As anode materials for sodium ion batteries, the outside carbon shell inhibits the serious volume change caused by Na+ insertion/extraction, and the Cu3Ge alloy enhances the sodiation capacity with rapid electron transfer and fast reaction kinetics. Corresponding kinetic analysis indicates pseudocapacitive behaviors play a dominant role in the total capacity at high rates. Hence, the Cu3Ge-NC exhibits favorable rate capability and cycling stability, which delivers a reversible capacity of 160 mAh g−1 for 500 cycles at a current density of 100 mA g−1.

The conductive 3D freestanding N-doped carbon nanofibers (NCNFs) current collector was embedded with homogeneously polar TiO2 nanoparticles. This current collector used for the sulfur cathode exhibits strong chemical adsorption for hindering the shuttle effect of polysulfides, and demonstrates a high specific capacity of 865 mA h g−1 at 0.2C and excellent cycle performance (200 cycles with capacity retention of 91%).

Lithium–sulfur batteries (LSBs) have shown great potential as a rival for next generation batteries, for its relatively high theoretical capacity and eco‐friendly properties. Nevertheless, blocked by the shuttle effect of lithium polysulfides (LPSs, Li2S4‐Li2S8) and insulation of sulfur, LSBs show rapid capacity loss and cannot achieve the practical application. Herein, a composite of carbon nanofibers coated by Co3S4 nanosheets (denoted as CNF@Co3S4) is successfully synthesized as freestanding sulfur host to optimize the interaction with sulfur species. The combination of the two materials can lead extraordinary cycling and rate performance by alleviating the shuttle of LPSs effectively. N‐doped carbon nanofibers serve as long‐range conductive networks and Co3S4 nanosheets can accelerate the conversion of LPSs through its electrocatalytic and chemical adsorption ability. Benefiting from the unique structure, the transporting rate of Li+ can be enhanced. Distribution of Li+ is uniform for enough exposed negative active sites. As a result, the cell with CNF@Co3S4 as sulfur host is able to stabilize at 710 mA h g−1 at 1 C after 200 cycles with average coulombic efficiency of 97.8% in a sulfur loading of 1.7 mg cm−2 and deliver 4.1 mA h cm−2 at 0.1 C even in 6.8 mg cm−2 for 100 cycles.

Transition metal chalcogenides especially Fe-based selenides for sodium storage have the advantages of high electric conductivity, low cost, abundant active sites, and high theoretical capacity. Herein, we proposed a facile synthesis of Fe

Germanium (Ge)‐based materials have been considered as potential anode materials for sodium‐ion batteries owing to their high theoretical specific capacity. However, the poor conductivity and Na+ diffusivity of Ge‐based materials result in retardant ion/electron transportation and insufficient sodium storage efficiency, leading to sluggish reaction kinetics. To intrinsically maximize the sodium storage capability of Ge, the nitrogen doped carbon‐coated Cu3Ge/Ge heterostructure material (Cu3Ge/Ge@N‐C) is developed for enhanced sodium storage. The pod‐like structure of Cu3Ge/Ge@N‐C exposes numerous active surface to shorten ion transportation pathway while the uniform encapsulation of carbon shell improves the electron transportation, leading to enhanced reaction kinetics. Theoretical calculation reveals that Cu3Ge/Ge heterostructure can offer decent electron conduction and lower the Na+ diffusion barrier, which further promotes Ge alloying reaction and improves its sodium storage capability close to its theoretical value. In addition, the uniform encapsulation of nitrogen‐doped carbon on Cu3Ge/Ge heterostructure material efficiently alleviates its volume expansion and prevents its decomposition, further ensuring its structural integrity upon cycling. Attributed to these unique superiorities, the as‐prepared Cu3Ge/Ge@N‐C electrode demonstrates admirable discharge capacity, outstanding rate capability and prolonged cycle lifespan (178 mAh g−1 at 4.0 A g−1 after 4000 cycles)., Nitrogen doped carbon‐coated Cu3Ge/Ge heterostructure is developed as anode material for fast and longevous sodium storage. Cu3Ge/Ge heterostructure efficiently promotes the Na+ diffusion and electron conduction in the composite, which enhances the sodium storage capability of Ge and accelerates its redox reaction kinetics. Attributed to the structural superiorities, a remarkable discharge capacity, superb rate capability and enhanced cyclic stability can be realized.

Lithium–sulfur batteries (LSBs) have shown great potential as a rival for next generation batteries, for its relatively high theoretical capacity and eco‐friendly properties. Nevertheless, blocked by the shuttle effect of lithium polysulfides (LPSs, Li2S4‐Li2S8) and insulation of sulfur, LSBs show rapid capacity loss and cannot achieve the practical application. Herein, a composite of carbon nanofibers coated by Co3S4 nanosheets (denoted as CNF@Co3S4) is successfully synthesized as freestanding sulfur host to optimize the interaction with sulfur species. The combination of the two materials can lead extraordinary cycling and rate performance by alleviating the shuttle of LPSs effectively. N‐doped carbon nanofibers serve as long‐range conductive networks and Co3S4 nanosheets can accelerate the conversion of LPSs through its electrocatalytic and chemical adsorption ability. Benefiting from the unique structure, the transporting rate of Li+ can be enhanced. Distribution of Li+ is uniform for enough exposed negative active sites. As a result, the cell with CNF@Co3S4 as sulfur host is able to stabilize at 710 mA h g−1 at 1 C after 200 cycles with average coulombic efficiency of 97.8% in a sulfur loading of 1.7 mg cm−2 and deliver 4.1 mA h cm−2 at 0.1 C even in 6.8 mg cm−2 for 100 cycles., CNF@Co3S4 as a freestanding sulfur host optimizes the interaction between sulfur species and the host material by the polarity and catalytical effect of Co3S4 nanosheets. The electronegative property of Co3S4 can further alleviate the growth of Li‐dendrites through realizing the uniform Li+ flux and deposition. These advantages guarantee extraordinary cycling and rate performance of corresponding Li–S batteries.

Cu2Se with high theoretical capacity and good electronic conductivity have attracted particular attention as anode materials for sodium ion batteries (SIBs). However, during electrochemical reactions, the large volume change of Cu2Se results in poor rate performance and cycling stability. To solve this issue, nanosized-Cu2Se is encapsulated in 1D nitrogen-doped carbon nanofibers (Cu2Se-NC) so that the unique structure of 1D carbon fiber network ensures a high contact area between the electrolyte and Cu2Se with a short Na+ diffusion path and provides a protective matrix to accommodate the volume variation. The kinetic analysis and DNa+ calculation indicates that the dominant contribution to the capacity is surface pseudocapacitance with fast Na+ migration, which guarantees the favorable rate performance of Cu2Se-NC for SIBs.

Additional file 1: Scheme S1. Preparation process of Co9S8@NSC. Figure S1. BJH pore width distribution of Co9S8@NSC (a) and NSC (b). Figure S2. N 1 s XPS spectra of Co9S8@NSC. Figure S3. (a-c) SEM and (d-f) TEM of NSC at different magnification. (The inset of (f) is the SAED of NSC.) Figure S4. EDS mapping of Co9S8@NSC. Figure S5. (a) CV curves of NSC with different cycles at 0.1 mV s-1; (b) Charge-discharge profiles of NSC at various cycles at 200 mA g-1. Figure S6. (a) Nyquist plots of Co9S8@NSC and (b) NSC before and after cycles; EIS curves comparison between Co9S8@NSC and NSC for initial (c), 5 cycles later (d) and 10 cycles later (e). Figure S7. The linear relation between Ip and v1/2 according to the Randles-Sevick equation.

A series of novel visible light driven all-solid-state Z-scheme BiOBr0.3I0.7/Ag/AgI photocatalysts were synthesized by facile in situ precipitation and photo-reduction methods. Under visible light irradiation, the BiOBr0.3I0.7/Ag/AgI samples exhibited enhanced photocatalytic activity compared to BiOBr0.3I0.7 and AgI in the degradation of methyl orange (MO). The optimal ratio of added elemental Ag was 15%, which degraded 89% of MO within 20 min. The enhanced photocatalytic activity of BiOBr0.3I0.7/Ag/AgI can be ascribed to the efficient separation of photo-generated electron–hole pairs through a Z-scheme charge-carrier migration pathway, in which Ag nanoparticles act as electron mediators. The mechanism study indicated that ·O2 − and h+ are active radicals for photocatalytic degradation and that a small amount of ·OH also participates in the photocatalytic degradation process.

Germanium based sulfides are potentially attractive as anode material for sodium ion batteries but rarely investigated. Herein, we firstly investigated Na+ storage properties of pristine Cu2GeS3 (PCGS) and found an effective strategy to improve its performance by a single lithiation/delithiation cycle obtaining ultrafine nanoparticle copper germanium sulfide (NCGS). The lithiation/delithiation process leads to the formation of a stable Li-containing solid electrolyte interphase film and a significant improvement of sodiation kinetics. Therefore, the NCGS anode delivers favorable capacity retention and better rate capability compared with that of a PCGS whether in the half cell or in the full cell, showing great promise for energy storage application.

Development of cheap, abundant and noble-metal-free materials as high efficient oxygen reduction electrocatalysts is crucial for future energy storage system. Here, one-dimensional (1D) MnO N-doped carbon nanofibers (MnO-NCNFs) were successfully developed by electrospinning combined with high temperature pyrolysis. The MnO-NCNFs exhibit promising electrochemical performance, methanol tolerance, and durability in alkaline medium. The outstanding electrocatalytic activity is mainly attributed to several issues. First of all, the uniform 1D fiber structure and the conductive network could facilitate the electron transport. Besides, the introduction of Mn into the precursor can catalyze the transformation of amorphous carbon to graphite carbon, while the improved graphitization means better conductivity, beneficial for the enhancement of catalytic activity for oxygen reduction reaction (ORR). Furthermore, the porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites, thus improve utilization efficiency and raise the quantity of exposed ORR active sites. The synergistic effect of MnO and NCNFs matrix, which enhances charge transfer, adsorbent transport, and delivers efficiency in the electrolyte solution, ensures the high ORR performance of MnO-NCNFs.

There are several drawbacks to the current oxygen reduction reaction (ORR) involving the kinetically sluggish process and expensive catalysts which impede the mass production of noble-metal materials for application in clean and efficient energy conversion devices. Herein, a type of ultrafine carbon nanoparticle with high nitrogen doping concentration can be simply prepared from a conveniently available precursor through a green and cost-effective hydrothermal process. With the aid of water, not only is the product's specific surface area enlarged, but the pore structure is also enriched, and there is improvement in the degree of graphitization and nitrogen-doped content. Meanwhile, the size of the carbon particle can be readily tuned to a nanoscale by changing the duration of the hydrothermal reaction. Interestingly, electrocatalytic activity is dramatically enhanced with the transformation of the carbon size and nitrogen structure. The characterization reveals that we have achieved a highly satisfactory electrocatalytic activity for ORR, a relatively positive onset potential of −0.02 V (vs. Hg/HgO) in alkaline media and 0.55 V (vs. Ag/AgCl) in acidic media, a higher diffusion-limiting current density than that of Pt/C, as well as outstanding stability and superior tolerance durability to methanol. Both the simplicity of the operation and the employed biomass precursor exactly meet the criteria for significant cost-saving, easy scale-up and eco-friendly demands for energy storage.

In order to overcome severe capacity fading of Ni-rich layered oxides Li[Ni1-x-yCoxMny]O2 cathode of lithium-ion battery at elevated voltage, a composite membrane consisting of poly(ethylene terephthalate) (PET) nonwoven fabric incorporated with poly(ethyl α-cyanoacrylate) was investigated as polymer matrix of gel polymer electrolyte (GPE). The ionic conductivity of the GPE based on this composite membrane saturated with a liquid electrolyte (LE) of 1 M LiPF6 in carbonate solvents is 2.54 mS cm−1 at room temperature, and the stable electrochemical voltage window can be up to 4.7 V. Its electrochemical performance is evaluated by using full cell with Li[Ni0.5Co0.2Mn0.3]O2 as cathode and graphite as anode. These results demonstrate that the as-prepared GPE remarkably improves the cyclability at the high cut-off voltage compared to the commercial liquid electrolyte. Keywords: Lithium-ion battery, High voltage, Polymer electrolyte, Poly(ethyl α-cyanoacrylate)

Li metal anode is promising materials for high-energy-density Li metal batteries (LMBs) due to its large theoretical specific capacity and negative reduction potential. However, the poor safety and insufficient cyclability caused by the dendritic Li growth hinder the commercialization of LMBs. To alleviate the formation of Li dendrites and further improve the cycling stability of LMBs, an ion-conductive polyacrylonitrile (PAN)-based hybrid separator is proposed. The hybrid separator is composed of flexible PAN and high ionic conductive W-doped Li6·3La3Zr1·65W0·35O12 (LLZWO) as the function of physical blocking to realize the Li dendrite-free. As a result, the hybrid separator with 20 wt% LLZWO (PLL-20) shows high ionic conductivity (6.89 × 10−5 S cm−1) and high Li-ion transference number (0.58). The Li|PLL-20|Li symmetric cells exhibit long-term stability without Li dendrite growth at 0.2 mA cm−2 for over 350 h. Furthermore, the Li|PLL-20|LiFePO4 battery delivers a high discharge specific capacity of 138.2 mAh g−1 at 0.2C under ambient conditions. This work highlights the ability of hybrid functional separators to protect Li metal anode in high-energy-density LMBs.

Co3V2O8 (CVO) with high theoretical specific capacity derived from the multiple oxidation states of V and Co is regarded as a potential electrode material for lithium-ion batteries (LIBs). Herein, reduced graphene oxide (rGO)-supported ultrafine CVO (rGO@CVO) nanoparticles are successfully prepared via the hydrothermal and subsequent annealing processes. The CVO supported on 2D rGO nanosheets possess excellent structural compatibility for the accommodation of volume variation to maintain the structural integrity of an electrode during the repeated lithiation/delithiation process. On the other hand, the rGO, as a highly-conductive network in the rGO@CVO composite, facilitates rapid charge transfer to ensure fast reaction kinetics. Moreover, the CV kinetic analysis indicates that the capacity of rGO@CVO is mainly dominated by a pseudocapacitive process with favorable rate capability. As a result, the rGO@CVO composite exhibits improved specific capacity (1132 mAh g&minus, 1, 0.1 A g&minus, 1) and promising rate capability (482 mAh g&minus, 1, 10 A g&minus, 1).

Cu2Se with high theoretical capacity and good electronic conductivity have attracted particular attention as anode materials for sodium ion batteries (SIBs). However, during electrochemical reactions, the large volume change of Cu2Se results in poor rate performance and cycling stability. To solve this issue, nanosized-Cu2Se is encapsulated in 1D nitrogen-doped carbon nanofibers (Cu2Se-NC) so that the unique structure of 1D carbon fiber network ensures a high contact area between the electrolyte and Cu2Se with a short Na+ diffusion path and provides a protective matrix to accommodate the volume variation. The kinetic analysis and DNa+ calculation indicates that the dominant contribution to the capacity is surface pseudocapacitance with fast Na+ migration, which guarantees the favorable rate performance of Cu2Se-NC for SIBs.

Atomically modified graphitic carbon nitride quantum dots (QDs), characterized by strongly increased reactivity and stability, are developed. These are deposited on arrays of TiO2 nanopillars used as a photoanode for the photoelectrochemical water splitting. This photoanode shows excellent stability, with 111 h of continuous work without any performance loss, which outperforms the best‐reported results by a factor of 10. Remarkably, our photoanode produces hydrogen even at zero bias. The excellent performance is attributed to the enhancement of photoabsorption, as well as to the promotion of charge separation between TiO2 nanopillars and the QDs.

Herein, we synthesized BiOBr/ultrathin g-C3N4/ternary heterostructures modified with black phosphorous quantum dots using a simple water bath heating and sonication method. The ternary heterostructure was then used for the photocatalytic degradation of tetracycline in visible light, with an efficiency as high as 92% after 3 h of irradiation. Thus, the photodegradation efficiency is greatly improved compared to that of ultrathin g-C3N4, BiOBr, and black phosphorous quantum dots alone. The synthesized ternary heterostructure improves the charge separation efficiency, thus increasing the photodegradation efficiency. This work provides a new and efficient method for the degradation of antibiotics in the environment.

The conductive 3D freestanding N-doped carbon nanofibers (NCNFs) current collector was embedded with homogeneously polar TiO

Germanium is considered as a potential anode material for sodium-ion batteries due to its fascinating theoretical specific capacity. However, its poor cyclability resulted from the sluggish kinetics and large volume change during repeated charge/discharge poses major threats for its further development. One solution is using its ternary compound as an alternative to improve the cycling stability. Here, high-purity CuGeO3 nanowires were prepared via a facile hydrothermal method, and their sodium storage performances were firstly explored. The as-obtained CuGeO3 delivered an initial charge capacity of 306.7 mAh g−1 along with favorable cycling performance, displaying great promise as a potential anode material for sodium ion batteries.

In this study, ternary Cu2SnS3 (CTS) nanostructure materials with high crystallinity were successfully prepared via a facile solvothermal method, which was followed by high-temperature treatment. The morphology of the as-synthesized samples is uniform flower-like spheres, with these spheres consisting of hierarchical nanosheets and possessing network features. Sodium storage measurements demonstrate that the annealed CTS electrodes have high initial reversible capacity (447.7 mAh&middot, g&minus, 1 at a current density of 100 mA&middot, 1), good capacity retention (200.6 mAh&middot, 1 after 50 cycles at a current density of 100 mA&middot, 1) and considerable rate capability because of their high crystallinity and unique morphology. Such good performances indicate that the high crystallinity CTS is a promising anode material for sodium ion batteries.

We present a feasible method for the preparation of one-dimensional N-doping carbon nanofibers encapsulated NaTi2(PO4)3 (NTP-NCNFs) through electrospinning accompanied by calcination. The poor electrical conductivity of NTP is significantly improved and the as-prepared NTP-NCNFs exhibit stable and ultrafast sodium-storage capability. The NTP-NCNFs maintains a stable specific capacity of 121 mAh g−1 at 10 C after 2,000 cycles, which only drop to 105 mAh g−1 after 20,000 cycles. Furthermore, the NTP-NCNFs show excellent rate performance from 0.2 to 20 C, whose recovery efficiency still reaches 99.43%. The superior electrochemical property is mainly attributed to the large specific surface area, high porosity, N-doping carbon coating, and one-dimensional structure of NTP-NCNFs.

Ni3S2 attracts much attention for sodium batteries owing to its natural abundance, low cost, and high theoretical capacity. However, poor conductivity of Ni3S2 and large volume expansion hamper its potential application. We describe a facile strategy to construct monolithic Ni3S2-Poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes with stable electrochemical performance for sodium batteries. Ni3S2 is directly grown on Ni foam substrate with superior electron transport efficiency. The PEDOT layer would efficiently protect the Ni3S2 from being wrecked by the severe volume expansion during charge–discharge process. The as-prepared Ni3S2-PEDOT electrodes display stable cycling performance with a capacity of 280 mAh g−1 after 30 cycles between 0.5 and 2 V. Keywords: Sodium batteries, Ni3S2, PEDOT, Monolithic Ni3S2-PEDOT electrode

Conjugated microporous polymers, which exhibit high specific capacity, superior cycle stability and remarkable rate capability, are explored as high-performance electrode materials for lithium and sodium storage. Their excellent electrochemical performance can be attributed to their conductive frameworks, plentiful redox-active units, high specific surface area and homogeneous microporous structure.