Hierarchical NiCo2Se4 nanoneedles/nanosheets with N-doped 3D porous graphene architecture as free-standing anode for superior sodium ion batteries

Hollow CoSe2-ZnSe microspheres inserted in reduced graphene oxide serving as advanced anodes for sodium ion batteries

Transition metal selenides are promising anode candidates for sodium ion batteries (SIBs) because of their higher theoretical capacity and conductivity than metal oxides. However, the disadvantages of severe capacity degradation and poor magnification performance greatly limit their commercial applications. Herein, we have developed a new hollow bimetallic selenides (CoSe2-ZnSe)@reduced graphene oxide (rGO) composite with abundant heterointerfaces. The rGO could not only alleviate the volume variations of hollow CoSe2-ZnSe microspheres during cycling, but also improve the conductivity of composite. The presence of the heterointerfaces could help to accelerate ionic diffusion kinetics and improve electron transfer, resulting in the improved sodium storage performance. As an advanced anode for SIBs, the CoSe2-ZnSe@rGO exhibits an enhanced initial coulombic efficiency of 75.1% (65.2% of CoSe2@rGO), extraordinary rate capability, and outstanding cycling stability (540.3 mAh/g at 0.2 A/g after 150 cycles, and 395.2 mAh/g at 1 A/g after 600 cycles). The electrochemical mechanism was also studied by kinetic analysis, showing that the charging/discharging process of CoSe2-ZnSe@rGO is mostly related to a capacitive-controlled behavior.

Rich-grain-boundary Ni-Co-Se nanowire arrays for fast charge storage in alkaline electrolyte

In this work, the one-dimensional (1D) Ni-Co-Se nanowire arrays with rich grain-boundaries were prepared through the solvothermal method and gas-phase selenizaiton. The results showed that the structure and crystallization of the Ni-Co-Se nanowire arrays could be modulated through the optimization of selenizaiton time. The optimal Ni-Co-Se electrode sample displayed an area specific capacitance of 242.6μAh cm-2at 30 mA cm-2with a current retention rate of 68.34%. The assembled Ni-Co-Se/Active carbon (AC) electrode-based asymmetric supercapacitor (ASC) showed the area specific capacitances of 329.2μAh cm-2and 225.8μAh cm-2at 3 mA cm-2and 30 mA cm-2, respectively. A 73.33% retention rate of capacitance was observed after 8000 charge/discharge cycles. Besides, the further fabricated all-solid ASC delivered the power densities of 342.94 W kg-1and 3441.33 W kg-1at the energy densities of 37.62 Wh kg-1and 25.81 Wh kg-1, respectively. Those results suggested the potentials of the obtained Ni-Co-Se nanowire arrays as electrode material for the high-performance pseudocapacitors.

Bimetal Oxide Reduction-Induced Perforation Strategy for Preparing a Multi-Microchannel Graphene-Based Anode Material with Rapid Sodium-Ion Diffusion

A sodium-ion battery, with a wide operating range, is much cheaper and safer than a lithium battery. Graphene is regarded as a promising carbon material in the preparation of anode materials. However, the large two-dimensional (2D) graphene sheets restrain the cross-plane diffusion of electrolyte ions, limiting the further improvement of rate performance. Herein, a nanohybrid of FeCo2Se4 and holey graphene (FeCo2Se4/HG) has been successfully prepared by the synchronism of pore creation and active material growth. Specifically, FeCo-oxide nanoparticles serve as the etching agents, generating in-plane nanoholes and subsequently converted into FeCo2Se4. The nanoholes provide a high density of cross-plane diffusion channels for sodium ions, serving as ionic diffusion shortcuts between different graphene layers to accelerate ion transport across the entire electrode. The unique architecture endows FeCo2Se4/HG with superior rate capability (411.2 mA h g-1 at 20 A g-1) and a specific capacity of 432.4 mA h g-1 at 2.0 A g-1 after 2000 cycles with a capacity retention rate of 92.4%. Therefore, pore engineering makes it possible for holey graphene-based electrodes to achieve outstanding rate performance and superb cycling durability.

In-situ synthesis of FeS/N, S co-doped carbon composite with electrolyte-electrode synergy for rapid sodium storage

Pyrrhotite (FeS) is extensively investigated as the anode for low-cost sodium-ion batteries (SIBs) due to their natural abundance and high theoretical capacity. However, it suffers from significant volume expansion and poor conductivity. These problems can be alleviated by promoting sodium-ion transport and introducing carbonaceous materials. Here, FeS decorated on N, S co-doped carbon (FeS/NC) is constructed through a facile and scalable strategy, which is the best of both worlds. Moreover, to give full play to the role of the optimized electrode, ether-based and ester-based electrolytes are used for matching. Reassuringly, the FeS/NC composite displays a reversible specific capacity of 387 mAh g^-1 after 1000 cycles at 5A g^-1 in dimethyl ether electrolyte. The even distribution of FeS nanoparticles on the ordered framework of carbon guarantees a fast electron/Na-ion transport channel, and the reaction kinetics can be further accelerated in the dimethyl ether (DME) electrolyte, ensuring the excellent rate capability and cycling performance of FeS/NC electrodes for sodium-ion storage. This finding not only provides a reference for the introduction of carbon via in-situ growth protocol, but also demonstrates the necessity for electrolyte-electrode synergy in realizing efficient sodium-ion storage.

MOF derived cobalt-nickel bimetallic phosphide (CoNiP) modified separator to enhance the polysulfide adsorption-catalysis for superior lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have aroused great research interest due to their high theoretical capacity and high energy density. To further develop lithium-sulfur batteries, it has become more and more important to put more efforts in promoting the adsorption and rapid catalytic conversion of lithium polysulfides (LiPSs). Herein, Ni/Co bimetallic phosphides were encapsulated into nitrogen-doped dual carbon conductive network (NiCoP@NC) by annealing and phosphorizing Ni-ZIF-67 precursor at high temperature. Due to their numerous co-adsorption/catalytic sites and high conductivity of carbon skeleton, the encapsulated Ni/Co phosphides particles could significantly enhance the anchoring and catalytic conversion of LiPSs and provide ultrafast channels for Li⁺ transport. When used as a modified separator for LSBs, the cells displayed superior performance with an initial capacity of 1083.4 m Ah g^-1 at 0.5 C and outstanding cycle stability with a capacity decay rate of only 0.09% per cycle for 300 cycles. Besides, even at high sulfur loading (3.2 mg cm^-2), they still present satisfactory performance. Therefore, this study presents a novel strategy on how to use MOF derived bimetallic phosphides with chemical adsorption and catalytic conversion of polysulfides for high-power advanced lithium-sulfur batteries.

Three-dimensional porous reduced graphene oxide modified electrode for highly sensitive detection of trace rifampicin in milk

Antibiotic overuse poses a serious food safety problem. Therefore, it is of great importance to develop efficient assays that respond to antibiotics to establish early-warning mechanisms. Here, we prepared a three-dimensional (3D) porous reduced graphene oxide (pRGO) modified electrode, which was characterized by scanning electron microscopy and transmission electron microscopy. As a result of the introduction of the 3D pRGO film, the electrocatalytic activity was considerably improved, which could efficiently trigger the redox reaction of rifampicin (RIF). By employing differential pulse voltammetry, the reduction peak current of RIF showed a good linear relationship with the logarithm of the RIF concentration in the range 1.0 × 10^-9 to 1.0 × 10^-7 mol L^-1. The linear equation was i_p (-10^-6 A) = 3.11 + 0.28 log c_RIF (R² = 0.9908) with a detection limit of 2.7 × 10^-10 mol L^-1 (S/N = 3). Additionally, the final electrode displayed long stability, good reproducibility and high selectivity, and could detect trace RIF in milk with satisfactory results. This study reveals the great potential in utilizing 3D pRGO to develop efficient electrochemical sensors for safeguarding food safety.

Polypyrrole Modified MoS2 Nanorod Composites as Durable Pseudocapacitive Anode Materials for Sodium-Ion Batteries

As a typical two-dimensional layered metal sulfide, MoS₂ has a high theoretical capacity and large layer spacing, which is beneficial for ion transport. Herein, a facile polymerization method is employed to synthesize polypyrrole (PPy) nanotubes, followed by a hydrothermal method to obtain flower-rod-shaped MoS₂/PPy (FR-MoS₂/PPy) composites. The FR-MoS₂/PPy achieves outstanding electrochemical performance as a sodium-ion battery anode. After 60 cycles under 100 mA g⁻¹, the FR-MoS₂/PPy can maintain a capacity of 431.9 mAh g⁻¹. As for rate performance, when the current densities range from 0.1 to 2 A g⁻¹, the capacities only reduce from 489.7 to 363.2 mAh g⁻¹. The excellent performance comes from a high specific surface area provided by the unique structure and the synergistic effect between the components. Additionally, the introduction of conductive PPy improves the conductivity of the material and the internal hollow structure relieves the volume expansion. In addition, kinetic calculations show that the composite material has a high sodium-ion transmission rate, and the external pseudocapacitance behavior can also significantly improve its electrochemical performance. This method provides a new idea for the development of advanced high-capacity anode materials for sodium-ion batteries.

The rational design of nickel-cobalt selenides@selenium nanostructures by adjusting the synthesis environment for high-performance sodium-ion batteries

Different selenization products (from the perspectives of micromorphology and sodium storage performance) can be obtained via regulating the selenization environment.

General metal-organic framework-derived strategy to synthesize yolk-shell carbon-encapsulated nickelic spheres for sodium-ion batteries

Transition-metal compounds have attracted enormous attention as potential energy storage materials for their high theoretical capacity and energy density. However, the most present transition-metal compounds still suffer from severe capacity decay and limited rate capability due to the lack of robust architectures. Herein, a general metal-organic framework-derived route is reported to fabricate hierarchical carbon-encapsulated yolk-shell nickelic spheres as anode materials for sodium-ion batteries. The nickelic metal-organic framework (Ni-MOF) precursors can be in situ converted into hierarchical carbon-encapsulated Ni₂P (Ni₂P/C), NiS₂ (NiS₂/C) and NiSe₂ (NiSe₂/C) by phosphorization, sulfuration, and selenation reaction, respectively, and maintain their yolk-shell sphere-like morphology. The as-synthesized Ni₂P/C sample can deliver much lower polarization and discharge platform, smaller voltage gap, and faster kinetics in comparison with that of the other two counterparts, and thus achieve higher initial specific capacity (3222.1/1979.3 mAh g^-1) and reversible capacity of 765.4 mAh g^-1 after 110 cycles. This work should provide new insights into the phase and structure engineering of carbon-encapsulated transition-metal compound electrodes via MOFs template for advanced battery systems.

Ni3Se4@CoSe2 hetero-nanocrystals encapsulated into CNT-porous carbon interpenetrating frameworks for high-performance sodium ion battery

Core-shell structured Ni-ZIF-67@ZIF-8 derived bimetal selenides encapsulating into a 3D interpenetrating dual-carbon framework (Ni₃Se₄@CoSe₂@C/CNTs) have been designed and prepared via carbonization and subsequent selenization processes. In this hierarchical structure, Ni₃Se₄@CoSe₂ nanocrystals were uniformly dispersed into the 3D carbon frameworkstructure/carbon nanotubes networks, which greatly enhanced the electronic conductivity and further enabled ultrafast Na-ion diffusion kinetics. When used as anode materials of sodium ion battery (SIB), The Ni₃Se₄@CoSe₂@C/CNTs electrode delivered the excellent rate capability of 206 mA h g^-1 at 3 A g^-1 and marvelous cyclic stability with capacity retention of 243 mA h g^-1 after 600 cycles at 1 A g^-1. This research provides a new way to prepare bimetallic selenide derived from MOF precursor with amazing heterostructure as the advanced anode materials for SIBs.

Flexible core/shelled PPy@PANI nanotube porous films for hybrid supercapacitors

Flexibility of the films and the limited ion transport in the vertical direction of film highly restrict the development of flexible supercapacitors. Herein, we have developed hybrid porous films consisting of N-doped holey graphene nanosheets (NHGR) with abundant in-plane nanopores and the vertically aligned polyaniline nanowires arrays on polypyrrole nanotubes (PPy@PANI) via a two-step oxidative polymerization strategy and vacuum filtration. The rational design can efficiently shorten the diffusion path of electrons/ions, alleviate volume variation of electrodes during cycling, enhance electric conductivity of the hybrids, and while offer abundant active interfacial sites for electrochemical reaction. Benefiting from the distinctive structural and compositional merits, the obtained PPy@PANI/NHGR film electrode manifests an excellent electrochemical properties in terms of specific capacity (1348 mF cm^-2at a current density of 1 mA cm^-2), rate capability (81.2% capacitance retention from 1 to 30 mA cm^-2), and cycling stability (capacitance retention of 73.7% at 20 mA cm^-2after 7000 cycles). Matched with NHGR negative electrode, the assembled flexible all-solid-state asymmetric supercapacitor displays a remarkable areal capacitance of 359 mF cm^-2at 5 mA cm^-2, maximum areal energy density of 112.2μWh cm^-2at 3.747 mW cm^-2, and good flexibility at various bending angles while preserving stable cycling performance. The result shows the PPy@PANI/NHGR film with high flexibility and 3D ions transport channels is highly attractive for flexible energy storage devices.

A g-C3N4 self-templated preparation of N-doped carbon nanosheets@Co-Co3O4/Carbon nanotubes as high-rate lithium-ion batteries' anode materials

A novel N-doped graphene-like carbon nanosheets (CNs) and carbon nanotubes (CNTs)-encapsulated Co-Co₃O₄ nanoparticles (NPs) (CN@Co-Co₃O₄/CNTs) were synthesized successfully by a simple hydrothermal and annealing method with graphite carbon nitride (g-C₃N₄) as self-template. By annealing Co²⁺/g-C₃N₄ under N₂ atmosphere, g-C₃N₄ was transformed into CN/CNTs, and Co²⁺ was reduced into CoNPs which were embedded in CNs. Further annealing in air, a shell of Co₃O₄ was formed around CoNPs. The amount of CNs, CNTs, and CoNPs can be adjusted by changing the ratio of Co²⁺ in Co²⁺/g-C₃N₄. The graphene-like CNs provided a large number of active sites and a large specific surface area for loading lots of small CoNPs uniformly. The CNTs with a diameter of 100 nm could not only improve the conductivity but also provide a buffer space for the aggregation and volume expansion of Co₃O₄. CNTs also enlarged the interlayer distance of CNs, which prevented the re-stacking of CNs and provided great convince for the intercalation and de-intercalation of Li⁺. When applied for anode material of lithium-ion batteries, CN@Co-Co₃O₄/CNTs exhibited a high discharge capacity of 460.0 mAh g^-1 at 5000 mA g^-1 after 300 cycles with a Coulombic efficiency of 98% and excellent higher-rate capacity (401.0 mAh g^-1 at 2000 mA g^-1 and 329.0 mAh g^-1 at 5000 mA g^-1).