Here, we introduce a new strategy using urea for the synthesis of carbon-incorporated 2D Fe3O4 (2D-Fe3O4/C) nanoflakes under solvothermal conditions with the following pyrolysis process under an inert atmosphere. Thanks to the structural advantages of 2D-Fe3O4/C, including 2D flakes providing a larger accessible surface area and exposing more active sites, as well as carbon incorporation promoting electrical conductivity for faster charge transfer, the 2D-Fe3O4/C displays a high specific capacitance of 386 F g−1 at 1 A g−1 in a three-electrode system. More importantly, when further assembled into a hybrid supercapacitor with pre-synthesized NiCo-layered double hydroxides as positive electrodes, the assembled supercapacitor device delivers a high-energy density of 32.5 W h kg−1 at 400 W kg−1 and little capacitance loss with bending angles ranging from 0° to 180°. As another capacitive application in desalination, 2D-Fe3O4/C also shows a high desalination capacity of 28.5 mg g−1 over 7.5 min, which suggests a very high mean desalination rate of 3.8 mg g−1 min−1. Our results not only highlight the significance of 2D metal oxide nanosheets/nanoflakes, but also hold great potential for high-performance capacitive applications in supercapacitors and desalination.

https://pubs.rsc.org/en/content/articlepdf/2021/QM/D0QM00946F

Carbon-incorporated Fe3O4 nanoflakes: high-performance faradaic materials for hybrid capacitive deionization and supercapacitors

Recently, due to the excessive consumption of fossil energy and the intermittent nature of clean energy resources, electricity storage has attracted great attention from both academia and industry. Lithium ion batteries (LIBs) with high energy density have been widely used for portable energy storage systems. However, limited lithium resources cannot meet the demands for large-scale applications, especially the grid-scale energy storage. Owing to the abundant natural resources of sodium and the low price, sodium ion batteries (SIBs) have become potential substitutes for LIBs. Cathode materials are key components that determine the overall performance and entire cost of SIBs. However, the unstable structure and limited electrochemical performance make them difficult to meet the requirement of practical applications. This review summarizes the recent development of the cathode materials used for SIBs, and the modified strategies applied to improve their electrochemical performance. Finally, critical challenges and perspectives to promote the development of SIBs are also presented.

Recent progress of emerging cathode materials for sodium ion batteries

Synthesis of magnetic, durable and superhydrophobic carbon sponges for oil/water separation

https://onlinelibrary.wiley.com/doi/pdf/10.1002/eem2.12100

Nano-Ferric Oxide Embedded in Graphene Oxide: High-performance Electrocatalyst for Nitrogen Reduction at Ambient Condition

Efficient photocatalytic degradation of crystal violet under natural sunlight using Fe3O4/ZnO nanoparticles embedded carboxylate-rich carbon

Fe3O4@C nanoparticles with a 3D net-like structure were synthesized via a facile and scalable one-pot co-precipitation followed by a subsequent carbonization in an Ar atmosphere. Verified by scanning and transmission electron microscopy characterization, it can be seen that Fe3O4 nanoparticles with the size of 10–15 nm were embedded in a uniform carbon shell with a thickness of around 2 nm. Furthermore, the corresponding XRD and EDS analysis combined with TEM images also proved that the thin carbon layer on the nano-scale Fe3O4 was amorphous. The charge/discharge tests showed that Fe3O4@C composite delivered an excellent reversible capacity of 980 mAh g−1 after 100 cycles at a current density of 92.4 mA g−1, which was much higher than that of the pure Fe3O4 (170 mAh g−1) synthesized by the same method. The outstanding reversible capacity is attributed to the small size of Fe3O4 particles and the high conductivity and mechanical strength of the amorphous carbon layer, which accelerates the electron transfer and relieves structure collapse caused by mechanical stress, thus maintaining a superior electrochemical stability.

One-pot co-precipitation synthesis of Fe 3 O 4 nanoparticles embedded in 3D carbonaceous matrix as anode for lithium ion batteries

Recrystallization synthesis of disodium rhodizonate-conductive polyaniline composite with high cyclic performance as cathode material of sodium-ion battery

Fe/Fe3O4@r-GO composite nanocages with a hollow porous heterostructure, which look like “flower cluster,” are prepared by a mild, simple, and flexible method, followed by a thermal treatment. Metal-organic framework Prussian blue (PB), used as a precursor of Fe3O4, possesses a special hollow porous morphology, which is able to shorten transmission path and relives the mechanical stress during charge/discharge cycles. Verified by SEM and TEM characterizations, the Fe/Fe3O4 nanocage coated with uniform graphene sheets is achieved. Furthermore, XRD and XPS analysis combined with TEM results also prove that the composite is mainly composed of Fe, Fe3O4, and C. A series of electrochemical tests show that Fe/Fe3O4@r-GO composite electrodes exhibit a superior reversible capacity, rate capability, and cycling stability. The composite delivers a high reversible capability of 1200 mAh g−1 after 160 cycles at a current density of 100 mA g−1. Especially, when the current density is increased to 1000 mA g−1, the composite delivers a capacity of 455 mAh g−1. Even at a current density of 2000 mA g−1, a capacity of 355 mAh g−1 is retained. The outstanding electrochemical performances are mainly attributed to the integrity of hollow porous nanocube structure and doping of moderate graphene, which enables to promote the conductivity of electrode and build a continue network between Fe/Fe3O4 nanocubes to further accelerate ion/electron migration rate and relieve mechanical stress during cycles.

Preparation and electrochemical properties of Fe/Fe 3 O 4 @r-GO composite nanocage with 3D hollow structure

The invention relates to a preparing method of using a 'one-pot method' to synthesize a ferroferric oxide@carbon composite material. The preparing method solves the problems that an existing compositematerial is complex in technology, high in cost, harsh in reaction conditions and the like. According to the technical scheme, firstly, an iron source and ammonium hydroxide are subjected to an initial reaction under ultrasonic assisting stirring to obtain a ferroferric oxide solution containing an incomplete reaction; then a phenolic aldehyde mixed solution is added into the ferroferric oxide solution for a complete reaction to obtain a ferroferric oxide@phenolic resin solution; finally, the ferroferric oxide@phenolic resin solution obtained in step 2 is washed and dried to obtain ferroferric oxide@phenolic resin, then ferroferric oxide@phenolic resin is heated, and after cooling, a final product ferroferric oxide@carbon is obtained. The technological raw materials and method are simple,technological conditions are mild, the operation is simple, the production cycle is short, and the equipment investment and production cost are low.

Preparing method of using 'one-pot method' to synthesize ferroferric oxide@carbon composite material

Oxygen enriched boron nitride microspheres (BNOs) coated with nano-sized calcium borate (CB) were synthesised by a reverse micro-emulsion method, in which calcium chloride and sodium borate were selected as the calcium and boron source, respectively. The phase identification and chemical bonding of the composite were confirmed by X-ray driffraction (XRD) and FT-IR spectroscopy. The chemical composition and valence state were determined by X-ray photoelectron spectroscopy (XPS). The morphology and microstructure of the samples were characterised by transmission electron microscopy (TEM) along with surface area analysis. The tribological property of the microspheres as a wear resistance additive in base oil was evaluated by a four-ball tester. The results show that the strawberry-like BNO/CB nanocomposites were fabricated successfully and possess a relatively high friction-reducing and antiwear performance. After the addition of BNO/CB nanocomposites, the friction coefficients of the base oil decreased by 13.3 % while the diameter of the grinding spot decreased by 16.4 %.

Qing Ai

Papers

One-pot co-precipitation synthesis of Fe 3 O 4 nanoparticles embedded in 3D carbonaceous matrix as anode for lithium ion batteries

Recrystallization synthesis of disodium rhodizonate-conductive polyaniline composite with high cyclic performance as cathode material of sodium-ion battery

Preparation and electrochemical properties of Fe/Fe 3 O 4 @r-GO composite nanocage with 3D hollow structure

Preparing method of using 'one-pot method' to synthesize ferroferric oxide@carbon composite material

Reverse Micro-Emulsion Synthesis of Oxygen-Enriched Low-Friction Boron Nitride/Calcium Borate Microspheres