Facile Synthesis of Co3O4-Incorporated Multichannel Carbon Nanofibers for Electrochemical Applications

Hybrid CuSn nanosphere-functionalized Cu/Sn co-doped hollow carbon nanofibers as anode materials for sodium-ion batteries

To strengthen the electrochemical performance of anode materials for sodium-ion batteries, Cu/Sn co-doped hollow carbon nanofibers functionalized by hybrid CuSn nanospheres (CuSn/C@MCNF) were prepared by a simple electrospinning method. The microstructural characteristics of CuSn/C@MCNF confirmed the same doped elements and strong interactions in hybrid CuSn nanospheres and the hollow carbon nanofiber substrate. CuSn/C@MCNF has superior specific capacity, excellent conductivity and high cycling stability. In particular, the doped hollow carbon nanofiber substrate can facilitate Na+ transport and alleviate volume expansion during the process of sodium storage. When applied as an anode material for sodium-ion batteries, CuSn/C@MCNF can deliver a reversible capacity of 340.1 mA h g-1 at a large current density of 1 A g-1 for 1000 cycles and a high-rate capacity of 202.5 mA h g-1 at 4.0 A g-1, all superior to the corresponding Sn-SnOx@MCNF- and MCNF-based electrodes. This work provides a basic idea for future anode materials in high-performance sodium-ion batteries.

Square-Facet Nanobar MOF-Derived Co3O4@Co/N-doped CNT Core-Shell-based Nanocomposites as Cathode Materials for High-Performance Supercapacitor Studies

The binary as well as ternary nanocomposites of the square-facet nanobar Co-MOF-derived Co₃O₄@Co/N-CNTs (N-CNTs: nitrogen-doped carbon nanotubes) with Ag NPs and rGO have been synthesized via an easy wet chemical route, and their supercapacitor behavior was then studied. At a controlled pH of the precursor solution, square-facet nanobars of Co-MOF were first synthesized by the solvothermal method and then pyrolyzed under a controlled nitrogen atmosphere to get a core-shell system of Co₃O₄@Co/N-CNTs. In the second step, different compositions of Co₃O₄@Co/N-CNT core-shell structures were formed by an ex-situ method with Ag NPs and rGO moieties. Among several bare, binary, and ternary compositions tested in 6 M aqueous KOH electrolyte, a ternary nanocomposite having a 7.0:1.5:1.5 stoichiometric ratio of Co₃O₄@Co/N-CNT, Ag NPs, and rGO, respectively, reported the highest specific capacitance (3393.8 F g^-1 at 5 mV s^-1). The optimized nanocomposite showed the energy density, power density, and Coulombic efficiency of 74.1 W h.kg^-1, 443.7 W.kg^-1, and 101.3%, respectively, with excellent electrochemical stability. After testing an asymmetrical supercapacitor with a Co₃O₄@Co/N-CNT/Ag NPs/rGO/nickel foam cathode and an activated carbon/nickel foam anode, it showed 4.9 W h.kg^-1 of energy density and 5000.0 W.kg^-1 of power density.

A Review on Non-Enzymatic Electrochemical Biosensors of Glucose Using Carbon Nanofiber Nanocomposites

Diabetes mellitus has become a worldwide epidemic, and it is expected to become the seventh leading cause of death by 2030. In response to the increasing number of diabetes patients worldwide, glucose biosensors with high sensitivity and selectivity have been developed for rapid detection. The selectivity, high sensitivity, simplicity, and quick response of electrochemical biosensors have made them a popular choice in recent years. This review summarizes the recent developments in electrodes for non-enzymatic glucose detection using carbon nanofiber (CNF)-based nanocomposites. The electrochemical performance and limitations of enzymatic and non-enzymatic glucose biosensors are reviewed. Then, the recent developments in non-enzymatic glucose biosensors using CNF composites are discussed. The final section of the review provides a summary of the challenges and perspectives, for progress in non-enzymatic glucose biosensors.

Electrospinning-Based Carbon Nanofibers for Energy and Sensor Applications

Carbon nanofibers (CNFs) are the most basic structure of one-dimensional nanometer-scale sp2 carbon. The CNF’s structure provides fast current transfer and a large surface area and it is widely used as an energy storage material and as a sensor electrode material. Electrospinning is a well-known technology that enables the production of a large number of uniform nanofibers and it is the easiest way to mass-produce CNFs of a specific diameter. In this review article, we introduce an electrospinning method capable of manufacturing CNFs using a polymer precursor, thereafter, we present the technologies for manufacturing CNFs that have a porous and hollow structure by modifying existing electrospinning technology. This paper also discusses research on the applications of CNFs with various structures that have recently been developed for sensor electrode materials and energy storage materials.

In Situ Construction of ZIF-67-Derived Hybrid Tricobalt Tetraoxide@Carbon for Supercapacitor

The Co3O4 electrode is a very promising material owing to its ultrahigh capacitance. Nevertheless, the electrochemical performance of Co3O4-based supercapacitors is practically confined by the limited active sites and poor conductivity of Co3O4. Herein, we provide a facile synthetic strategy of tightly anchoring Co3O4 nanosheets to a carbon fiber conductive cloth (Co3O4@C) using the zeolitic imidazolate framework-67 (ZIF-67) sacrificial template via in situ impregnation and the pyrolysis method. Benefiting from the enhancement of conductivity and the increase in active sites, the binder-free porous Co3O4@C supercapacitor electrodes possess typical pseudocapacitance characteristics, with an acceptable specific capacitance of ~251 F/g at 1 A/g and long-term cycling stability (90% after cycling 5000 times at 3 A/g). Moreover, the asymmetric and flexible supercapacitor composed of Co3O4@C and activated carbon is further assembled, and it can drive the red LED for 6 min.

Lithium-Sulfur Batteries Meet Electrospinning: Recent Advances and the Key Parameters for High Gravimetric and Volume Energy Density

Lithium-sulfur (Li-S) batteries have been regarded as a promising next-generation energy storage technology for their ultrahigh theoretical energy density compared with those of the traditional lithium-ion batteries. However, the practical applications of Li-S batteries are still blocked by notorious problems such as the shuttle effect and the uncontrollable growth of lithium dendrites. Recently, the rapid development of electrospinning technology provides reliable methods in preparing flexible nanofibers materials and is widely applied to Li-S batteries serving as hosts, interlayers, and separators, which are considered as a promising strategy to achieve high energy density flexible Li-S batteries. In this review, a fundamental introduction of electrospinning technology and multifarious electrospinning-based nanofibers used in flexible Li-S batteries are presented. More importantly, crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density are emphasized based on the proposed mathematic model, in which the electrospinning-based nanofibers are used as important components in Li-S batteries to achieve high gravimetric (WG ) and volume (WV ) energy density of 500 Wh kg-1 and 700 Wh L-1 , respectively. These systematic summaries not only provide the principles in nanofiber-based electrode design but also propose enlightening directions for the commercialized Li-S batteries with high WG and WV .

CuCoNi–S anchored CoMoO4/MoO3 forming core–shell structure for high-performance asymmetric supercapacitors

CoMoO4/MoO3@CuCoNi–S is prepared by hydrothermal and electrodeposition methods. It offers promising supercapacitor properties.

Facile synthesis of Ni(OH)2 nanoarrays on graphene@carbon fabric as dual-functional electrochemical materials for supercapacitors and capacitive desalination

A high-performance Ni(OH)₂ nanoarray on graphene (RGO)@carbon fabric nanocomposites with hierarchical nanostructures were facilely synthesized, which involves (i) coating of graphene on a carbon fabric; and (ii) in situ growth of Ni(OH)₂ nanoarray on the graphene surface. It was found that Ni(OH)₂ nanoplates grew evenly on the surface of graphene without stacking. This unique structure of the electrode material favors a higher electrochemical active site, endowing the enhancing capacity performance. The morphology and microstructure of the as-prepared composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques. Capacitive properties of the as-synthesized electrodes were studied via cyclic voltammetry, charge/discharge, and electrochemical impedance spectroscopy in a three-electrode experimental setup. Taking advantage of the unique structure of Ni(OH)₂/RGO@carbon fabric nanocomposites, this material as dual-functional electrodes shows decent performance for both supercapacitors and capacitive desalination (CDI). The specific capacitance was calculated to be 1325 F g⁻¹ at 1 A g⁻¹; moreover, this material shows a high rate capability, whereby the capacitance can be maintained at 612 F g⁻¹ even at 10 A g⁻¹. Besides, its performance as potential CDI electrodes was explored. Such high-performance Ni(OH)₂/RGO@carbon fabric hierarchical nanostructures can offer great promise in large-scale energy storage device applications.

This work reported the synthesis of dual-functional electrode Ni(OH)₂ nanoarrays on RGO@carbon fabric nanocomposites with hierarchical nanostructures. The electrode showed decent performance on both supercapacitor and CDI.

Grain boundary enriched CuO nanobundle for efficient non-invasive glucose sensors/fuel cells

Glucose oxidation reaction (GOR) plays a significant role in glucose fuel cells anode and glucose sensors. Therefore, optimizing the GOR catalyst nanostructure is auxiliary to their efficient operation. In this study, we present a cascade-assembled strategy to prepare CuO nanobundles (CuO-NB) with high-density and homogenous grainboundaries (GBs). The essence of activity in GOR that depended on GBs are thoroughly investigated. The increased glucose diffusion coefficient of CuO-NB means that GBs has a faster glucose mass transfer, which is attributed to the terraces in GBs dislocation surface. Furthermore, the accumulation of electrons on GBs makes the glucose adsorption increased and the free energy of dehydrogenation step decreased, leading to a lower glucose oxidation barrier. Therefore, CuO-NB is appropriate for non-invasive glucose detection and glucose fuel cells. This study sheds new light on the GBs effect in GOR and paves the way for developing high-efficiency electrocatalysts.

Recent advance in the fabrication of carbon nanofiber-based composite materials for wearable devices

Carbon nanofibers (CNFs) exhibit the advantages of high mechanical strength, good conductivity, easy production, and low cost, which have shown wide applications in the fields of materials science, nanotechnology, biomedicine, tissue engineering, sensors, wearable electronics, and other aspects. To promote the applications of CNF-based nanomaterials in wearable devices, the flexibility, electronic conductivity, thickness, weight, and bio-safety of CNF-based films/membranes are crucial. In this review, we present recent advances in the fabrication of CNF-based composite nanomaterials for flexible wearable devices. For this aim, firstly we introduce the synthesis and functionalization of CNFs, which promote the optimization of physical, chemical, and biological properties of CNFs. Then, the fabrication of two-dimensional and three-dimensional CNF-based materials are demonstrated. In addition, enhanced electric, mechanical, optical, magnetic, and biological properties of CNFs through the hybridization with other functional nanomaterials by synergistic effects are presented and discussed. Finally, wearable applications of CNF-based materials for flexible batteries, supercapacitors, strain/piezoresistive sensors, bio-signal detectors, and electromagnetic interference shielding devices are introduced and discussed in detail. We believe that this work will be beneficial for readers and researchers to understand both structural and functional tailoring of CNFs, and to design and fabricate novel CNF-based flexible and wearable devices for advanced applications.

Application of Electrospun Nanofibers for Fabrication of Versatile and Highly Efficient Electrochemical Devices: A Review

Electrochemical devices convert chemical reactions into electrical energy or, vice versa, electricity into a chemical reaction. While batteries, fuel cells, supercapacitors, solar cells, and sensors belong to the galvanic cells based on the first reaction, electrolytic cells are based on the reversed process and used to decompose chemical compounds by electrolysis. Especially fuel cells, using an electrochemical reaction of hydrogen with an oxidizing agent to produce electricity, and electrolytic cells, e.g., used to split water into hydrogen and oxygen, are of high interest in the ongoing search for production and storage of renewable energies. This review sheds light on recent developments in the area of electrospun electrochemical devices, new materials, techniques, and applications. Starting with a brief introduction into electrospinning, recent research dealing with electrolytic cells, batteries, fuel cells, supercapacitors, electrochemical solar cells, and electrochemical sensors is presented. The paper concentrates on the advantages of electrospun nanofiber mats for these applications which are mostly based on their high specific surface area and the possibility to tailor morphology and material properties during the spinning and post-treatment processes. It is shown that several research areas dealing with electrospun parts of electrochemical devices have already reached a broad state-of-the-art, while other research areas have large space for future investigations.

Hybrid supercapacitors using electrodes from fibers comprising polymer blend-metal oxide composites with polymethacrylic acid as chelating agent

Hybrid supercapacitors (SCs) made of carbon-metal oxide composites are devices which combine the advantages of electric double layer capacitors and pseudocapacitors viz high energy density, high power density and high cyclability. This is best achieved when the pseudocapacitive components are uniform in size and distribution on the conducting carbon support. Electrodes mats, fabricated from carbonized electrospun fibers generated from solutions of polyacrylonitrile (PAN) as the carbon source, cobalt (III) acetylacetonate as a metal oxide precursor, and polymethacrylic acid (PMAA) as a metal oxide precursor carrier were utilized in coin cell SCs. Fibers without the PMMA carrier were prepared for comparison. XRD and TGA showed conversion of the cobalt precursor to a mixture of cobalt and cobalt oxide (Co₃O₄). When the PMAA carrier was used, specific capacitance increased from 68 F g^-1in PAN-Co₃O₄to 125 F g^-1in PAN-PMAA-Co₃O₄. The addition of PMAA to the system results in better uniformity, accessibility and dispersion of metal and metal oxide particles. Due to the relatively low surface area of carbonized samples, Co₃O₄nanoparticles are the primary contributors to charge storage. The fabricated fibers show an energy density of 8.9 at 750 W kg^-1, which is twice that of the fibers made without PMAA.

Fabrication of Co3O4 nanoparticle-decorated porous activated carbon electrode for the electrochemical detection of 4-nitrophenol

Preparation of Co3O4@BVFC for the electrochemical detection of 4-NP.

Self-template formation of porous Co3O4 hollow nanoprisms for non-enzymatic glucose sensing in human serum

A novel type of porous Co₃O₄ hollow nanoprism (HNP) was successfully prepared using tetragonal cobalt acetate hydroxide [Co₅(OH)₂(OAc)₈·2H₂O] as precursor by a facile solvothermal process and a subsequent calcination treatment. The morphology and structure of the Co₃O₄ HNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and N₂ adsorption–desorption measurements. An enzyme-free glucose sensor was constructed based on the Co₃O₄ HNPs, and the electrochemical performance was tested by cyclic voltammetry (CV) and chronoamperometry. The as-prepared sensor exhibited a good electrocatalytic activity for glucose oxidation at the applied potential of 0.6 V in alkaline solution, with a high sensitivity of 19.83 μA mM⁻¹ cm⁻² and a high upper limit of 30 mM, which provide the potential for direct determination of blood glucose without any dilution pretreatment. The Co₃O₄ HNPs had a porous and tubular structure with a large amount of accessible active sites, which enhanced the mass diffusion and accelerated the electron transfer. Moreover, the sensor also demonstrated a desirable stability, selectivity and reproducibility, and could verify the non-enzymatic analysis of glucose in real samples.

Co₃O₄ hollow nanoprisms based non-enzymatic glucose sensor were prepared by a self-template process, exhibiting wide linear range, good selectivity and stability, which can directly monitoring blood glucose without any dilution pretreatment.