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Aqueous zinc ion batteries (ZIBs) have attracted extensive attention because of its high cost-performance and high safety. This study reports a structural engineering method that embeds Mn ions as pillars into the VO2 layered structure, and improves the morphology through polyvinylpyrrolidone (PVP) to increase the specific surface area, thereby obtaining MnVO2-PVP. Increasing the number of electrochemically active sites allows it to have faster ion diffusion kinetics and better long-term cycle stability. The synthesized MnVO2-PVP with nanoprism and nanosheet composite structure shows a remarkable capacity of 470.2 mAh g-1 at 0.5 A g-1, and also has excellent cycle stability at 5000 times at 10 A g-1. The capacity after cycling is 176.5 mAh g-1, with high energy density (179 W h kg-1) and power density (7000 W kg-1). The synthesis method and marvelous performance of MnVO2-PVP can lay a foundation for the improvement of the synthesis method of ZIBs cathode materials in the future.

In the past decades, energy storage devices have drawn widespread attention in diverse fields including hybrid electric vehicles and smart portable electronics. By taking advantage of two different electrode materials, asymmetric supercapacitors (ASCs) can extend their operating voltage window and display more excellent energy-storage capacity than those of symmetric supercapacitors. Recent developments demonstrated that transition metal sulfides (TMSs) have emerged as a promising class of materials for ASCs due to their low cost, fascinating redox reversibility and electronic conductivity. In this review, the latest progresses in various types of TMS-based electrode materials for ASCs are summarized. Particularly, the study places emphasis on the impact of morphological control and composite engineering on the final electrochemical performances of the materials. Moreover, some effective strategies and potential challenges for further development of TMS-based electrode materials are discussed. It is believed that an in-depth understanding would be a guide for designing TMSs with ideal electrochemical performances in the future.

Co9S8/Mo2S3 nanorods on CoS2 laminar arrays (CoS2-Co9S8/Mo2S3, defined as Co1Mo1) were synthesized via one step hydrothermal method for high performance supercapacitors. The Co1Mo1 hybrid was in-situ grown on Ni foam (NF). The nanorods and laminar arrays constructed 3D network with stable structure, maintaining high durability during electrochemical reactions. What’s more, this Co1Mo1 hybrid electrode combined the merits of both cobalt sulfides (the high capacity) and molybdenum sulfides (the excellent cycling stability). As expected, the Co1Mo1//NF hybrid exhibited excellent capacitance (2777.5 F g−1 at 1 A g−1), wonderful rate performance (81.46% from 1 to 50 A g−1), as well as superior stability (100% at 10 A g−1 after 8500 cycling) when used as single electrodes. The Co1Mo1//AC device was also assembled, showing high energy density (56.56 Wh kg−1 at the power density of 850 W kg−1). When combined two Co1Mo1//AC devices in series, six colored led bulbs which were in parallel can be lighted (green LED, working voltage greater than 3 V), further corroborated the possibility of the Co1Mo1 electrode for practical application. This study provided an easy and low-cost method for synthesizing electrode materials with excellent electrochemical performance.

Rational design and synthesis of hybrid structures consisting with multiple pseudocapacitive components are challenging to develop materials with a high energy density for conversion and storage applications. Herein, a novel and cost-effective two-step method has been developed to synthesize three-dimensional (3D) nickel cobalt sulfides (Ni-Co-S)/Co(OH)2 nanocomposite with synergistic effect to provide an excellent comprehensive electrochemical performance, which shows a high specific capacitance (1560.8 Fg−1 at 1 A g−1) and outstanding rate capability (953.3 Fg−1 at 30 A g−1). Subsequently, an all-solid-state asymmetric supercapacitor (ASC) was successfully assembled using Ni1-Co2-S/Co(OH)2 nanocomposite as the positive electrode, activated carbon (AC) as the negative electrode and an alkaline PVA gel (PVA/KOH) as electrolyte. The Ni1-Co2-S/Co(OH)2//AC all-solid-state ASC device with a voltage window of 1.6 V delivered a maximum energy density of 48.8 W h kg−1 at a power density of 800 W kg−1 with excellent cycle stability. Excitedly, two all-solid-state ASCs assembled in series under fully charged can effectively light up four parallel connected light-emitting diodes (LEDs) for around 10 min, and can power a white LED (working voltage, 3.0–3.4 V) effectively. These remarkable electrochemical performances of Ni1-Co2-S/Co(OH)2//AC are beneficial to their practical applications for high-performance energy storage.

Recently, aqueous zinc-ion batteries (ZIBs) are highly attractive due to high specific capacity of Zn, low-cost and safety, but the weak reaction kinetics and fast capacity attenuation still remain challenging. Herein, we adopt a temperature-regulation method to prepare rough Mn-doped zinc oxide microspheres. Such microsphere structure is rich in superfine nanoparticles and internal mesopores, which offers more Zn2+ diffusion channels and alleviates the stress and strain in the electrochemical process. Meanwhile, the doping of Mn into the ZnO structure can not only adjust the electronic structure, but also enhance the electrical conductivity, thereby upraising the reaction kinetics. Applied to ZIBs cathode, Mn-doped ZnO material presents appreciable rate performance, which obtains 268.1 mA h g−1 at 1 A g−1 and retains 163.8 mA h g−1 at 5 A g−1. Most importantly, high energy density (206.9 Wh kg−1), power density (6896.7 W kg−1) and superior cycle durability (~146.7% after 10 000 cycles relative to the first cycle) endow this material with more potential in energy storage.

Constructing the supercapacitive materials which featured with abundant contact area and high conductivity is suitable for rapid ions/electrons transport. Herein, ultrathin Ni-Zn hydroxide nanosheets are vertically aligned on reduced graphene oxide (rGO) via MOF templates, and such sandwich-like structure is featured with abundant electrolytes-accessible contact sites. Introducing porous rGO substrate with excellent electronic conductivity can not only greatly accelerate the electron transfer between current collector and hydroxide, but also depress the agglomeration of hydroxide. Besides, heterogenous Zn element is also doped into the Ni-based hydroxide, which greatly optimizes the inherent electronic structure and conductivity of Ni-based hydroxide. Benefited from sandwich-like structure, the introduction of rGO and Zn doping, such Ni-Zn hydroxide/rGO material has harvested abundant contact sites and high conductivity. As a result, this supercapacitive material is featured with suitable capacitance (615.4C g−1 at 1 A g−1), appropriate stability (87.5% after 8000 cycles) and superior capacity rate property (62.3% retention at 30 A g−1). To well disclose the energy-storage feature of this material, a corresponding hybrid supercapacitor is manufactured, which presents a high capacity of 234.3C g−1 at 1 A g−1, superior capacity retention (89.7% retention after 10,000 cycles) and excellent energy density (53.7 Wh kg−1 at 825.1 W kg−1). These fascinating results demonstrate the excellent supercapacitive performance of this Ni-Zn hydroxide/rGO material.

Effective bifunctional catalysts are desirable to replace precious metal materials to promote the development of electrochemical water splitting. Facing with challenge, it is important to design and construct bifunctional electrocatalysts. Herein, we present a highly efficient multifunctional electrocatalyst, i.e., metal-organic framework derived Co3O4@Mo-Co3S4-Ni3S2/NF. (NF: nickle foam). Nano-flowers supported by the nanorods directly grown on the conductive substrate are achieved by doping non-3d high-valence metal Mo during the sulfurization process of ZIF-67 precursor. As a result, the obtained Co3O4@Mo-Co3S4-Ni3S2/NF heterostructure shows outstanding electrochemical performance. Specifically, the low overpotentials of 295 mV and 116 mV are obtained at the current densities of 50 mA cm−2 and 10 mA cm−2 for OER and HER in an alkaline solution, respectively. Moreover, Co3O4@Mo-Co3S4-Ni3S2/NF exhibited excellent catalytic activity with a current density of 10 mA cm−2 at a low voltage of 1.62 V for overall water splitting. This study may provide new methods for metal doping and rationally constructing heterostructure to improve electrochemical performance of catalysts, and is expected to help accelerate progress towards the non-precious metal electrocatalysts for overall water splitting.

Exploiting efficient and rechargeable lithium-ion batteries (LIBs) is of great significance, which stimulates us to procure suitable electrode materials. Herein, a novel anode material is fabricated via encasing CoxZn1-xS/Co9S8 nanoparticles into N-doped reduced graphene oxide (rGO) skeleton. Owing to the open and accessible structure constructed by the conductive rGO as well as the optimized Co:Zn ratio, the as-prepared electrodes achieve good lithium storage capacity (742.2 mAh g−1 at 1 A g−1 and 222.4 mAh g−1 at 10 A g−1) and an excellent retention rate of 105.9% on 1000th cycle at 1 A g−1, making them promising anode candidate for highly reversible lithium storage in long-term cycles.

For achieving the long cycle and high capacity of supercapacitive materials, the emphasis lies in ameliorating conductivity, regulating phase content and constructing porous structure. In such case, we synthesize a hierarchical hollow (Ni,Co)Se2 nanocubes@reduced graphene oxide (rGO) via the procedures of co-precipitation, selenation and rGO coating treatments. The hollow structure and ultra-thin nanosheets are conducive to rapid OH− diffusion. The tailored Ni: Co ratio, coupled with weak-electronegativity Se, is beneficial to adjusting the electronic structure of hybrid structure. Meanwhile, the existing porous rGO is not only served as conductive network to improve conductivity, but also acted as the structure protector and space separator to maintain structural integrality. Benefiting from such merits in the content and morphology, the (Ni,Co)Se2@rGO electrode is featured with specific capacity (649.1C g−1 at 1 A g−1), ultrahigh rate performance (75.5% at 20 A g−1) together with outstanding cycling stability (90.5% retention after 5000 times charge/discharge at 10 A g−1). Moreover, the resulting (Ni,Co)Se2@rGO//activated carbon (AC) hybrid supercapacitor (HSC) achieves high energy density of 52.6 Wh kg−1 at 803.4 W kg−1 and remarkable cycling lifespan (~100% retention over 10,000 cycles), further eliciting the tremendous potentiality of such (Ni,Co)Se2@rGO material.

Recently, establishing lithium-ion battery electrodes (LIBs) with high activity and high mass loading is propitious to high-performance lithium storage. Herein, a facile metal salt-immersion approach followed by sintering treatment is exhibited to prepare porous iron oxides/ hollow tubular carbon cloth (HCC) electrode. An optimal sintering temperature of 700 °C not only creates electrolyte-accessible HCC current collector, but also tunes the surface structure and internal compositions of adherent iron oxides, thereby boosting the lithium-ion diffusion kinetics. This as-prepared integrated electrode delivers a high areal capacity of 5.46 mAh cm−2 (at 0.2 mA cm−2). For fully cognizing the advantages of our integrated electrode, we are further devoted to exploring the electrochemical mechanism and physical superposition of multi-layer electrodes. The experimental data demonstrate that, repeated conversion-type reaction could transform Fe3O4-FeO hybrid structure into finer Fe3O4 nanoparticles with rich oxygen vacancy (Vo). The density functional theory (DFT) discloses that, forming Vo sites in Fe3O4 structure could significantly upraise electrical conductivity and Li+ diffusion, which benefits to stabilizing the electrochemical performance. For both several-fold promoting mass loading and maintaining loading thickness at a finite electrode area, the single-layer, double-layer and triple-layer integrated electrodes are assembled into LIBs, which exhibits high average capacities of 5.33, 9.23 and 11.12 mAh cm−2. Toward several electronic equipments, the double-layer electrodes exhibit a long endurance time, further validating the superior energy-storage capacity.

Constructing high specific area and porous micro-nano frameworks is suitable for fast electrons/ions transport, which motivates us to design hollow polyhedra with multi-order structure. However, the synthesis route of hollow polyhedra is still restricted due largely to the complexity and high cost. Herein, the finding in rational design and one-pot hydrothermal synthesis of porous hollow nickel-cobalt-manganese hydroxide (NiCoMn-OH) polyhedra is reported, using zeolitic imidazolate framework-67 (ZIF-67) as the templates. The ultrathin edge-to-face stacking nanosheets construct a three-dimensional multi-order hollow polyhedral structure with internal nanoporous channels, which can stimulate electron/ion transfer. Toward the application in supercapacitor, the NiCoMn-OH electrode presented superior capacitance performance (1654.5 F g−1 at 1 A g−1) and excellent rate performance (58.5% retention at 30 A g−1) in a three electrode alkaline system. Moreover, the quasi-solid-state NiCoMn-OH//AC device was also fabricated, exhibiting excellent capacitance of 121.5 F g−1 at 1 A g−1, high energy density of 43.2 Wh kg−1 at a power density of 0.79 kW kg−1, and outstanding capacitance retention (100% retention after 10,000 cycles). Also, the suitable energy supply capacity of NiCoMn-OH electrode was further validated, via utilizing two quasi-solid-state NiCoMn-OH//AC devices to trigger light-emitting diode (LED) bulbs.

In this contribution, a series of CoFe 2− x M x O 4 (M = Al 3+ , In 3+ and Cu 2+ ) ferrites were synthesized by a facile hydrothermal method. On the premise of spinel structure, the coercive forces and adsorption capabilities of the doped CoFe 2 O 4 ferrites are significantly enhanced. It is first reported that coercive field of magnetic material shows more important influence on the adsorption capacity than that of specific surface area. Water magnetized mechanism was proposed to explain the relation between the coercive field and adsorption capacity. To the best of our knowledge, the CR adsorption value of 605.4 mg g −1 may be the best among the reported magnetic adsorbents with spinel structure.

Amorphous iron oxide (IO) nanoparticles (NPs) with excellent water-solubility were synthesized at room temperature without the presence of any solvents. The obtained nanoparticles were characterized by FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), EDS (energy dispersive X-ray spectroscopy), X-Ray photoelectron spectroscopy (XPS), and TEM (transmission electron microscopy). T 2 -weighted MRI images of citrate-coated NPs showed that the magnetic resonance signal is enhanced significantly with increasing nanoparticle concentration in water. Advantages of this method rely not only on the simplicity and nontoxicity but also on the low cost, highly suitable for further applications. These results indicate that the citrate-coated NPs have great potential for application in MRI as a T 2 contrast agent.

We report a facile oleic acid-assisted hydrothermal route to synthesize NaYF 4 :Yb/Er crystals doped by alkali ions (Li + or K + ions), and the effects of alkali ion doping on the crystal structure and upconversion (UC) fluorescence emission of the NaYF 4 :Yb,Er crystals are investigated in detail. With the increasing dosage of Li + ions in the NaYF 4 :Yb/Er crystals, their morphologies are changed from rod to disk and finally to polyhedron. However, the morphologies of NaYF 4 :Yb/Er crystals doped with K + ions almost keep the rod-like shape. In addition, the phase transition of Li x Na 1− x YF 4 crystals initiates when x is equal to or larger than 0.5, but the phase of K y Na 1− y YF 4 remains unchanged even if y reaches 0.85. Furthermore, the UC emission intensity of NaYF 4 :Yb/Er crystals reduces with the doping of Li + ions. On the contrary, the UC emission intensity of NaYF 4 :Yb/Er crystals increases as K + ions are introduced. It is interesting that the green and red UC emissions of the K 0 . 7 Na 0.3 YF 4 :Yb,Er crystal are high 8 and 7 times, respectively.

Here, we are going to report a simple, low-cost and environmental friendly process to prepare catenulate flowery iron (Fe). Magnetite (FeFe 2 O 4 ) with similar 3D morphology is gained at room temperature for the first time by aging of iron in water. The saturation magnetizations of these two products are totally high, which are 121.59 emu/g for Fe and 90.2 emu/g for FeFe 2 O 4 . It is not usual for Fe 3 O 4 with lamellar structure because magnetic saturation for well defined Fe 3 O 4 single crystals is 92 emu/g. Because of the special appearance with large surface area, adsorption experiments of organic dye, sulfonamide and heavy metal ions are carried out in synthetic wastewater. Adsorption rate of two magnetic samples—iron and magnetite—can achieve more than 98% in 5 min. It is worthy to note that, in adsorption experiment of Cr VI , the adsorption rate of Fe can achieve 100% in 5 min. The equilibrium times of all productions can be controlled in a short span of 30 min. Achieve high performance of adsorption in a short time, which perform a great advantage in water treatment applications of such materials. Finally, regeneration experiments of FeFe 2 O 4 which adsorbed Congo red show that the as prepared sample can be well-regenerated, and after regeneration, the magnetic adsorbents can still show more than 97.6% adsorption capacity.

In this contribution, we compare the adsorption capacity of different MFe2O4 (M = Mn, Fe, Co, Ni) ferrite nanocrystals synthesized by hydrothermal method for Congo red (CR). It is the first time to give a comprehensive comparison and analysis of the adsorption capacity of ferrite nanocrystals with spinel structure for CR. Research indicates that the cations distribution of MFe2O4 ferrites is the most important factor to decide their adsorption capacity. Electrostatic absorption was conceived as the main adsorption mechanism. Meanwhile, the MFe2O4 nanoparticles exhibited a clearly ferromagnetic behavior under applied magnetic field, which allowed their high-efficient magnetic separation from wastewater. Furthermore, acetone is an effective desorption agent for desorption of MFe2O4 nanoparticles loaded by CR. All of the spinel ferrite nanocrystals possess good soft-magnetism, especially, CoFe2O4 nanocrystals exhibit a higher saturation magnetization of 86.1 emu g−1 as well as the outstanding adsorption capacity for CR. By the calculation of Langmuir isotherm model, the maximum adsorption capacity of CoFe2O4 for CR is 244.5 mg g−1.

Fe 3 O 4 spheres with loose structure assembled by nanospheres with diameters around 50 nm are synthesized via a facile one-pot solvothermal method. Series of Fe 3 O 4 morphologies are obtained by controlling the concentration of cetyltrimethylammonium bromide (CTAB). The saturation magnetization of Fe 3 O 4 nanospheres is about 87.3 emu/g. Adsorption ability and mechanism of all samples are investigated. Experiments demonstrate that adsorption capacity is closely related with the double impacts of electrostatic interactions and specific surface area.

Magnetic Co chains with different morphologies have been successfully prepared with a facile solvothermal method by introducing 1,3-propanediamine (PDA). The prepared Co sub-micro chains possess particular magnetism and high thermal stability, which shows more practical and profound application. During the solvothermal process, the sizes and morphologies of Co chains are successfully controlled by adjusting the dosage of PDA and the reaction temperature. In particular, the growth of Co chains involves an oriented attachment process because the adjacent particles attach at a planar interface for removing the higher surface energy. Moreover, the different types of dislocation present at interface, while the densities of dislocation are increased with the rise in reaction temperature.