Engineering Mesoporous Single Crystals Co-Doped Fe2O3 for High-Performance Lithium Ion Batteries

A crosslinked network polypyrrole coated cobalt doped Fe2O3@carbon cloth flexible anode material for quasi-solid asymmetric supercapacitors

Iron(III) oxide (Fe2O3) exhibits a substantial theoretical specific capacitance and a broad operational voltage window, making it a prospective anode material. The crystal structure of Fe2O3 was altered through cobalt doping, and its electronic conductivity was improved by supporting it with carbon cloth (Co-Fe2O3@CC). Subsequently, a crosslinked network of polypyrrole (PPy) was synthesized onto Co-Fe2O3@CC via an ice-water bath, resulting in the formation of PPy/Co-Fe2O3@CC. This PPy nano-crosslinked network not only established three-dimensional electron transport pathways on the Fe2O3 surface but also amplified the composite material's specific surface area to 45.229 m2 g-1, thereby promoting its electrochemical performance. At a current density of 2 mA cm-2, PPy/Co-Fe2O3@CC displayed an area specific capacitance of 704 mF cm-2, a value 2.2 times higher than that of Co-Fe2O3@CC. The assembled PPy/Co-Fe2O3@CC//Ni-MnO2@CC asymmetric supercapacitor demonstrated an energy density of 1.41 mW h cm-3 at a power density of 54 mW cm-3, making the synthesized electrode material a promising candidate for flexible supercapacitors.

Preparation and Evaluation of Co-Doped Fe7S8/C Composites for Lithium Storage

Fe₇S₈ has a high theoretical capacity (663 mAh g^-1) and can be prepared at a low cost, making it advantageous for production. However, Fe₇S₈ has two disadvantages as a lithium-ion battery anode material. The first is that the conductivity of Fe₇S₈ is not good. The second is that when the lithium ion is embedded, the volume expansion of the Fe₇S₈ electrode is serious. That is why Fe₇S₈ has not been used in real life yet. In this paper, Co-Fe₇S₈/C composites were prepared by doping Co into Fe₇S₈ through a one-pot simple hydrothermal method. In situ Co is doped into Fe₇S₈ to produce a more disordered microstructure to improve ion and electron transport performance, thereby reducing the activation barrier of the main material. The Co-Fe₇S₈/C electrode presents a high specific discharge capacity of 1586 mAh g^-1 and a Coulombic efficiency (CE) of 71.34% at an initial cycle at 0.1 A g^-1. After 1500 cycles, the specific discharge capacity remains at 436 mAh g^-1 (5 A g^-1). When the current density returns to 0.1 A g^-1, the capacity almost returns to the initial level, showing excellent rate performance.

Mesoporous Single Crystals with Fe-Rich Skin for Ultralow Overpotential in Oxygen Evolution Catalysis

The oxygen evolution reaction (OER) is a key reaction in water splitting and metal-air batteries, and transition metal hydroxides have demonstrated the most electrocatalytic efficiency. Making the hydroxides thinner for more surface commonly fails to increase the active site number, because the real active sites are the edges. Up to now, the overpotentials of most state-of-the-art OER electrocatalysts at a current density of 10 mA cm^-2 (η₁₀ ) are still larger than 200 mV. Herein, a novel design of mesoporous single crystal (MSC) with an Fe-rich skin to boost the OER is shown. The edges around the mesopores provide lots of real active sites and the Fe modification on these sites further improves the intrinsic activity. As a result, an ultralow η₁₀ of 185 mV is achieved, and the turnover frequency based on Fe atoms is as high as 16.9 s^-1 at an overpotential of 350 mV. Moreover, the catalyst has an excellent catalytic stability, indicated by a negligible current drop after 10 000 cyclic voltammetry cycles. The catalyst enables Zn-air batteries to run stably over 270 h with a low charge voltage of 1.89 V. This work shows that MSC materials can provide new opportunities for the design of electrocatalysts.

Single-Crystal Nano-Subunits Assembled Accordion-Shape WNb2 O8 Framework with High Ionic/Electronic Conductivities towards Li-Ion Capacitors

Recently, Li-ion capacitors (LICs) have drawn tremendous attention due to their high energy/power density along with long cycle life. Nevertheless, the slow kinetics and stability of the involved anodes as bottleneck barriers always result in the modest properties of devices. The exploration of advanced anodes with both high ionic and electronic conductivities as well as structural stability thus becomes more significant for practical applications of LICs. Herein, a single-crystal nano-subunits assembled hierarchical accordion-shape WNb₂ O₈ micro-/nano framework is first designed via a one-step scalable strategy with the multi-layered Nb₂ CT_x as a precursor. The underlying solid solution Li-storage mechanism of the WNb₂ O₈ just with a volumetric expansion of ≈1.5% is proposed with in situ analysis. Benefiting from congenitally crystallographic merits, single-crystalline characteristic, and open accordion-like architecture, the resultant WNb₂ O₈ as a robust anode platform is endowed with fast electron/ion transport capability and multi-electron redox contributions from W/Nb, and accordingly, delivers a reversible capacity of ≈135.5 mAh g^-1 at a high rate of 2.0 A g^-1 . The WNb₂ O₈ assembled LICs exhibit an energy density of ≈33.0 Wh kg^-1 at 9 kW kg^-1 , coupled with remarkable electrochemical stability. The work provides meaningful insights into the rational design and construction of advanced bimetallic niobium oxides for next-generation LICs.

Al-Doped Fe2O3 nanoparticles: advanced anode materials for high capacity lithium ion batteries

Al-Doped Fe2O3 (Al-Fe2O3) nanoparticles with a reconstructed electronic structure, oxygen vacancy and modified physical/chemical features are synthesized and used as an advanced anode for Lithium Ion Batteries (LIBs).

Preparation of multi-functional magnetic-plasmonic nanocomposite for adsorption and detection of thiram using SERS

Magnetic materials have been widely used for constructing substrate in surface enhanced Raman scattering (SERS) sensing due to the magnetic responsibility. Here, we reported a facile and effective approach to construct multi-functional SERS substrate based on assembling Ag nanoparticles (NPs) on porous Fe microspheres. The porous Fe microspheres were prepared through hydrogen reduction of Fe₂O₃ NPs with porous structure, in which the size and morphology of Fe could be well controlled. The surface of Fe was grafted with amino group, and then decorated with Ag NPs. The surface area and pore size of Fe microsphere were characterized by nitrogen adsorption and desorption. The Fe@Ag nanocomposite illustrated a good SERS activity. Furthermore, this substrate could be used for pesticide monitoring by portable Raman spectrometer. Especially, the porous Fe microsphere could adsorb analyte from target sample and the Fe@Ag could be concentrated by magnetic force to amplify the SERS signal for thiram detection.

Synthesis of cobalt-doped V2O3 with a hierarchical yolk–shell structure for high-performance lithium-ion batteries

Co-V₂O₃-24 yolk–shell nanospheres were synthesized via a solvothermal treatment and subsequent calcination. The electrochemical performance of Co-V₂O₃-24 is greatly improved because of Co-doping and the novel hierarchical yolk–shell structure.

Single-Crystal α-Fe2O3 with Engineered Exposed (001) Facet for High-Rate, Long-Cycle-Life Lithium-Ion Battery Anode

Designing electrode materials with engineered exposed facets provides a novel strategy to improve their electrochemical properties. However, the controllability of the exposed facet remains a daunting challenge, and a deep understanding of the correlation between exposed facet and Li⁺-transfer behavior has been rarely reported. In this work, single-crystal α-Fe₂O₃ hexagonal nanosheets with an exposed (001) facet are prepared with the assistance of aluminum ions through a one-step hydrothermal process, and structural characterizations reveal an Al³⁺-concentration-dependent-growth mechanism for the α-Fe₂O₃ nanosheets. Furthermore, such α-Fe₂O₃ nanosheets, when used as lithium-ion battery anodes, exhibit high specific capacity (1261.3 mAh g^-1 at 200 mA g^-1), high rate capability (with a reversible capacity of approximately 605 mAh g^-1 at 10 A g^-1), and excellent cyclic stability (with a capacity of over 900 mAh g^-1 during 500 cycles). The superior electrochemical performance of α-Fe₂O₃ nanosheets is attributed to the pseudocapacitive behavior, Al-doping in the α-Fe₂O₃ structure, and improved Li⁺-transfer property across the (001) facet, as elucidated by first-principles calculations based on density functional theory. These results reveal the underlying mechanism of Li⁺ transfer across different facets and thus provide insights into the understanding of the excellent electrochemical performance.

Biomimetic Straw-Like Bundle Cobalt-Doped Fe2 O3 Electrodes towards Superior Lithium-Ion Storage

Biomimetic straw-like bundles of Co-doped Fe₂ O₃ (SCF), with Co²⁺ incorporated into the lattice of α-Fe₂ O₃ , was fabricated through a cost-effective hydrothermal process and used as the anode material for lithium-ion batteries (LIBs). The SCF exhibited ultrahigh initial discharge specific capacity (1760.7 mA h^-1  g^-1 at 200 mA g^-1 ) and cycling stability (with the capacity retention of 1268.3 mA h^-1  g^-1 after 350 cycles at 200 mA g^-1 ). In addition, a superior rate capacity of 376.1 mA h^-1  g^-1 was obtained at a high current density of 4000 mA g^-1 . The remarkable electrochemical lithium storage of SCF is attributed to the Co-doping, which increases the unit cell volume and affects the whole structure. It makes the Li⁺ insertion-extraction process more flexible. Meanwhile, the distinctive straw-like bundle structure can accelerate Li ion diffusion and alleviate the huge volume expansion upon cycling.

Biomass-Mediated Synthesis of Cu-Doped TiO2 Nanoparticles for Improved-Performance Lithium-Ion Batteries

Pure TiO₂ and Cu-doped TiO₂ nanoparticles are synthesized by the biomediated green approach using the Bengal gram bean extract. The extract containing biomolecules acts as capping agent, which helps to control the size of nanoparticles and inhibit the agglomeration of particles. Copper is doped in TiO₂ to enhance the electronic conductivity of TiO₂ and its electrochemical performance. The Cu-doped TiO₂ nanoparticle-based anode shows high specific capacitance, good cycling stability, and rate capability performance for its envisaged application in lithium-ion battery. Among pure TiO₂, 3% Cu-doped TiO₂, and 7% Cu-doped TiO₂ anode, the latter shows the highest capacity of 250 mAh g^-1 (97.6% capacity retention) after 100 cycles and more than 99% of coulombic efficiency at 0.5 A g^-1 current density. The improved electrochemical performance in the 7% Cu-doped TiO₂ is attributed to the synergetic effect between copper and titania. The results reveal that Cu-doped TiO₂ nanoparticles might be contributing to the enhanced electronic conductivity, providing an efficient pathway for fast electron transfer.

Preparation of ZnFe2O4/α-Fe2O3 Nanocomposites From Sulfuric Acid Leaching Liquor of Jarosite Residue and Their Application in Lithium-Ion Batteries

Recycling Zn and Fe from jarosite residue to produce high value-added products is of great importance to the healthy and sustainable development of zinc industry. In this work, we reported the preparation of ZnFe₂O₄/α-Fe₂O₃ nanocomposites from the leaching liquor of jarosite residue by a facile chemical coprecipitation method followed by heat treatment at 800°C in air. The microstructure of the as-prepared ZnFe₂O₄/α-Fe₂O₃ nanocomposites were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy, scanning transmission electron microscope (STEM), and X-ray photoelectron spectrum (XPS). The results demonstrated that the ZnFe₂O₄/α-Fe₂O₃ composites are composed of interconnected ZnFe₂O₄ and α-Fe₂O₃ nanocrystals with sizes in the range of 20–40 nm. When evaluated as anode material for Li-ion batteries, the ZnFe₂O₄/α-Fe₂O₃ nanocomposites exhibits high lithium storage activity, superior cyclic stability, and good high rate capability. Cyclic voltammetry analysis reveals that surface pseudocapacitive lithium storage has a significant contribution to the total stored charge of the ZnFe₂O₄/α-Fe₂O₃, which accounts for the enhanced lithium storage performance during cycling. The synthesis of ZnFe₂O₄/α-Fe₂O₃ nanocomposites from the leaching liquor of jarosite residue and its successful application in lithium-ion batteries open up new avenues in the fields of healthy and sustainable development of industries.

Single step synthesized three dimensional spindle-like nanoclusters as lithium-ion battery anodes

A facile, green, mild and one-step conventional heating method was developed to synthesize monodisperse Sn-doped Fe₂O₃ nanoclusters with a novel spindle-like 3D architecture as anode materials for lithium-ion batteries.

Formation of Mn–Cr mixed oxide nanosheets with enhanced lithium storage properties

Novel carbon-free Mn₂O₃/MnCr₂O₄ hybrid nanosheets are synthesized. As an anode for lithium-ion batteries, they deliver a wonderful electrochemical performance.