High-performance lithium storage of Co3O4 achieved by constructing porous nanotube structure

Hierarchical structure promoted lithiation/delithiation behavior of a double-carbon microsphere supported nano-Co3O4 anode

Due to limited mass loading, high-capacity electrode materials such as transition metal oxides (TMOs) are essential for microscale Li-ion batteries (LIBs) integrated in nano-/micro-electromechanical systems (N/MEMS). Unfortunately, their electrochemical performances are largely plagued by severe mechanical degradation and slow electron transport. Therefore, it is crucial to develop strategies that can improve the structural stability and electronic conductivity of TMO electrodes. In this work, double-carbon (carbon nanotubes and ketjen black) microsphere (DCMS) supported Co3O4 electrodes are fabricated simply through a spray drying and solvothermal method, which are designed to have a mesoporous three-dimensional (3D) hierarchical heterostructure containing well-dispersed Co3O4 nanoparticles within the DCMS framework. An in situ transmission electron microscopy (TEM) study reveals that the DCMS framework can not only provide facile strain accommodation, but also good electronic conductivity, leading to a much improved Li-storage performance compared to other Co3O4-based anodes. The hierarchical electrode exhibits maximum charge capacities of 1205.2 and 678.1 mA h g-1 at current densities of 0.1 and 2 A g-1, respectively, as well as a capacity retention of 92.2% at 0.3 A g-1 after 100 cycles. This study provides a low-cost, simple and general method for developing advanced high-capacity electrodes.

One-Dimensional (1D) Nanostructured Materials for Energy Applications

At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal, and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized, which undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes, and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface-volume relationship, tunable thermal and transport properties, and its high surface area, these 1D nanostructures have become fundamental elements for the development of energy processes. The most relevant 1D nanomaterials, their different synthesis procedures, and useful methods for assembling 1D nanostructures in functional devices will be presented. Applications in relevant topics such as optoelectronic and photochemical devices, hydrogen production, or energy storage, among others, will be discussed. The present review concludes with a forecast on the directions towards which future research could be directed on this class of nanostructured materials.

Beyond the Single-Nozzle: Coaxial Electrospinning Enables Innovative Nanofiber Chemistries, Geometries, and Applications

With an ever increasing scientific, technological, and industrial interest in high surface area, porous nanofiber mats, electrospinning has emerged as a popular method to produce fibrous assemblies for use across biomedical, energy, and environmental applications. However, not all precursor solutions nor complex geometries can be easily fabricated using the traditional single-nozzle apparatus. Therefore, coaxial electrospinning, a modified version of electrospinning that features a concentrically aligned dual nozzle, has been developed. This review will first describe the mechanism of electrospinning two precursor solutions simultaneously and the operational parameters that need to be optimized to fabricate continuous fibers. Modifications that can be made to the coaxial electrospinning process, which enable the fabrication of uniform fibers with improved properties, as well as the fabrication of fibers that are hollow, functionalized, and from "nonspinnable precursors" will be discussed as a means of promoting the advantages of using a coaxial setup. Examples of how coaxially electrospun nanofibers are employed in diverse applications will be provided throughout this review. We conclude with a timely discussion about the current limitations and challenges of coaxial electrospinning.

Coaxial Electrospinning Formation of Complex Polymer Fibers and their Applications

The formation of fibers by electrospinning has experienced explosive growth in the past decade, recently reaching 4,000 publications and 1,500 patents per year. This impressive growth of interest is due to the ability to form fibers with a variety of materials, which lend themselves to a large and rapidly expanding set of applications. In particular, coaxial electrospinning, which forms fibers with multiple core-sheath layers from different materials in a single step, enables the combination of properties in a single fiber that are not found in nature in a single material. This article is a detailed review of coaxial electrospinning: basic mechanisms, early history and current status, and an in-depth discussion of various applications (biomedical, environmental, sensors, energy, catalysis, textiles). We aim to provide readers who are currently involved in certain aspects of coaxial electrospinning research an appreciation of other applications and of current results.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Metal-Oleate Complex-Derived Bimetallic Oxides Nanoparticles Encapsulated in 3D Graphene Networks as Anodes for Efficient Lithium Storage with Pseudocapacitance

In this manuscript, we have demonstrated the delicate design and synthesis of bimetallic oxides nanoparticles derived from metal-oleate complex embedded in 3D graphene networks (MnO/CoMn₂O₄ ⊂ GN), as an anode material for lithium ion batteries. The novel synthesis of the MnO/CoMn₂O₄ ⊂ GN consists of thermal decomposition of metal-oleate complex containing cobalt and manganese metals and oleate ligand, forming bimetallic oxides nanoparticles, followed by a self-assembly route with reduced graphene oxides. The MnO/CoMn₂O₄ ⊂ GN composite, with a unique architecture of bimetallic oxides nanoparticles encapsulated in 3D graphene networks, rationally integrates several benefits including shortening the diffusion path of Li⁺ ions, improving electrical conductivity and mitigating volume variation during cycling. Studies show that the electrochemical reaction processes of MnO/CoMn₂O₄ ⊂ GN electrodes are dominated by the pseudocapacitive behavior, leading to fast Li⁺ charge/discharge reactions. As a result, the MnO/CoMn₂O₄ ⊂ GN manifests high initial specific capacity, stable cycling performance, and excellent rate capability.

Highly Efficient Silver-Cobalt Composite Nanotube Electrocatalysts for Favorable Oxygen Reduction Reaction

This paper reports the synthesis and characterization of silver-cobalt (AgCo) bimetallic composite nanotubes. Cobalt oxide (Co₃O₄) nanotubes were fabricated by electrospinning and subsequent calcination in air and then reduced to cobalt (Co) metal nanotubes via further calcination under a H₂/Ar atmosphere. As-prepared Co nanotubes were then employed as templates for the following galvanic replacement reaction (GRR) with silver (Ag) precursor (AgNO₃), which produced AgCo composite nanotubes. Various AgCo nanotubes were readily synthesized with applying different reaction times for the reduction of Co₃O₄ nanotubes and GRR. One hour reduction was sufficiently long to convert Co₃O₄ to Co metal, and 3 h GRR was enough to deposit Ag layer on Co nanotubes. The tube morphology and copresence of Ag and Co in AgCo composite nanotubes were confirmed with SEM, HRTEM, XPS, and XRD analyses. Electroactivity of as-prepared AgCo composite nanotubes was characterized for ORR with rotating disk electrode (RDE) voltammetry. Among differently synthesized AgCo composite nanotubes, the one synthesized via 1 h reduction and 3 h GRR showed the best ORR activity (the most positive onset potential, greatest limiting current density, and highest number of electrons transferred). Furthermore, the ORR performance of the optimized AgCo composite nanotubes was superior compared to pure Co nanotubes, pure Ag nanowires, and bare platinum (Pt). High ethanol tolerance of AgCo composite nanotubes was also compared with the commercial Pt/C and then verified its excellent resistance to ethanol contamination.

Transition metal oxide hierarchical nanotubes for energy applications

We report a general synthetic method for transition metal oxide (TMO) hierarchical nanotube (HNT) structures by a solution-phase cation exchange method from Cu2O nanowire templates. This method leads to the formation of hollow, tubular backbones with secondary, thin nanostructures on the tube surface, which substantially increases the surface reactive sites for electrolyte contacts and electrochemical reactions. As proofs-of-concept, several representative first-row TMO HNTs have been synthesized, including CoOx, NiOx, MnOx, ZnOx and FeOx, with specific surface areas much larger than nanotubes or nanoparticles of corresponding materials. An example of the potential energy storage applications of CoOx HNTs as supercapacitors is also demonstrated.

Graphene-coated mesoporous Co3O4 fibers as an efficient anode material for Li-ion batteries

The graphene-coating porous cobalt oxide fibers (Co₃O₄@G) were synthesized using coordination polymers as precursors through calcination and subsequent self-assembly process. The obtained materials exhibit good electrochemical performances.

Mesoporous hybrid NiOx–MnOx nanoprisms for flexible solid-state asymmetric supercapacitors

Mesoporous hybrid NiO_x–MnO_x nanoprisms exhibit good performance as electrode materials for flexible solid-state symmetric supercapacitors.

CoOx nanoparticles embedded in porous graphite carbon nanofibers derived from electrospun polyacrylonitrile@polypyrrole core–shell nanostructures for high-performance supercapacitors

A novel composite nanostructure of C–CoO_x–C with CoO_x nanoparticles embedded in N-containing porous graphite carbon nanofibers exhibited a more acceptable specific capacitance, higher rate capability and better cycling stability.