A synthesis of graphene/Co3O4 thin films for lithium ion battery anodes by coelectrodeposition

Electrochemical approach toward reduced graphene oxide-based electrodes for environmental applications: A review

Graphene has shown great potential in various application fields due to its excellent carrier transportation, ultra-high specific surface area, good mechanical properties, and light transmittance. However, pure graphene still exhibits some insurmountable defects, such as difficulty in simple and large-scale preparation, and limitations in application. The electrochemical method is a simple, clean, and environmentally friendly method. The rapid and simple preparation of graphene and its derivatives by electrochemical methods has important environmental significance. Moreover, rGO-based nanohybrids can be prepared by convenient and quick electrodeposition or cyclic voltammetry (CV), or to change the morphology and structure of graphene and its derivatives to achieve the purpose of improving material properties. This work mainly summarizes electrochemically related graphene from four aspects: (i) the method of electrochemical exfoliation of graphene; (ii) types of electrodeposition rGO-based nanohybrids; (iii) electrochemical regulation of the structure of rGO-based mixtures; (iv) environmental applications of rGO-based nanohybrids prepared by electrodeposition. This article critically discusses the advantages and disadvantages of electrochemical-related graphene, outlines future challenges, and provides insightful views and references for other researchers.

Designed synthesis of ultrafine NiO nanocrystals bonded on a three dimensional graphene framework for high-capacity lithium-ion batteries

NiO nanocrystals/3D-GF nanohybrids are fabricated in situ and used for high-capacity lithium-ion batteries.

Graphene-Embedded Co3O4 Rose-Spheres for Enhanced Performance in Lithium Ion Batteries

Co₃O₄ has been widely studied as a promising candidate as an anode material for lithium ion batteries. However, the huge volume change and structural strain associated with the Li⁺ insertion and extraction process leads to the pulverization and deterioration of the electrode, resulting in a poor performance in lithium ion batteries. In this paper, Co₃O₄ rose-spheres obtained via hydrothermal technique are successfully embedded in graphene through an electrostatic self-assembly process. Graphene-embedded Co₃O₄ rose-spheres (G-Co₃O₄) show a high reversible capacity, a good cyclic performance, and an excellent rate capability, e.g., a stable capacity of 1110.8 mAh g^-1 at 90 mA g^-1 (0.1 C), and a reversible capacity of 462.3 mAh g^-1 at 1800 mA g^-1 (2 C), benefitted from the novel architecture of graphene-embedded Co₃O₄ rose-spheres. This work has demonstrated a feasible strategy to improve the performance of Co₃O₄ for lithium-ion battery application.

Synthesis of a Ni0.8Zn0.2Fe2O4–RGO nanocomposite: an excellent magnetically separable catalyst for dye degradation and microwave absorber

A Ni_0.8Zn_0.2Fe₂O₄ reduced graphene oxide nanocomposite has been synthesized by a simple ‘in situ co-precipitation’ technique.

Recent advances in graphene and its metal-oxide hybrid nanostructures for lithium-ion batteries

Today, one of the major challenges is to provide green and powerful energy sources for a cleaner environment. Rechargeable lithium-ion batteries (LIBs) are promising candidates for energy storage devices, and have attracted considerable attention due to their high energy density, rapid response, and relatively low self-discharge rate. The performance of LIBs greatly depends on the electrode materials; therefore, attention has been focused on designing a variety of electrode materials. Graphene is a two-dimensional carbon nanostructure, which has a high specific surface area and high electrical conductivity. Thus, various studies have been performed to design graphene-based electrode materials by exploiting these properties. Metal-oxide nanoparticles anchored on graphene surfaces in a hybrid form have been used to increase the efficiency of electrode materials. This review highlights the recent progress in graphene and graphene-based metal-oxide hybrids for use as electrode materials in LIBs. In particular, emphasis has been placed on the synthesis methods, structural properties, and synergetic effects of metal-oxide/graphene hybrids towards producing enhanced electrochemical response. The use of hybrid materials has shown significant improvement in the performance of electrodes.

Interwoven three-dimensional architecture of cobalt oxide nanobrush-graphene@Ni(x)Co(2x)(OH)(6x) for high-performance supercapacitors

Development of pseudocapacitor electrode materials with high comprehensive electrochemical performance, such as high capacitance, superior reversibility, excellent stability, and good rate capability at the high mass loading level, still is a tremendous challenge. To our knowledge, few works could successfully achieve the above comprehensive electrochemical performance simultaneously. Here we design and synthesize one interwoven three-dimensional (3D) architecture of cobalt oxide nanobrush-graphene@Ni(x)Co(2x)(OH)(6x) (CNG@NCH) electrode with high comprehensive electrochemical performance: high specific capacitance (2550 F g(-1) and 5.1 F cm(-2)), good rate capability (82.98% capacitance retention at 20 A g(-1) vs 1 A g(-1)), superior reversibility, and cycling stability (92.70% capacitance retention after 5000 cycles at 20 A g(-1)), which successfully overcomes the tremendous challenge for pseudocapacitor electrode materials. The asymmetric supercapacitor of CNG@NCH//reduced-graphene-oxide-film exhibits good rate capability (74.85% capacitance retention at 10 A g(-1) vs 0.5 A g(-1)) and high energy density (78.75 Wh kg(-1) at a power density of 473 W kg(-1)). The design of this interwoven 3D frame architecture can offer a new and appropriate idea for obtaining high comprehensive performance electrode materials in the energy storage field.

Three dimensional metal oxides–graphene composites and their applications in lithium ion batteries

The review focuses on the effects of morphology, composition and interaction of 3d metal oxide–graphene composites on the performances of libs.

Preparation of a reduced graphene oxide hydrogel by Ni ions and its use in a supercapacitor electrode

A three-dimensional (3D) reduced graphene oxide hydrogel (rGOH) was prepared by hydrothermal synthesis based on the electrostatic force and chemical reaction between graphene oxide (GO) and Ni ions in a nickel acetate solution.

Graphene-based nanocomposite anodes for lithium-ion batteries

Graphene-based nanocomposites have been demonstrated to be promising high-capacity anodes for lithium ion batteries to satisfy the ever-growing demands for higher capacity, longer cycle life and better high-rate performance. Synergetic effects between graphene and the introduced second-phase component are generally observed. In this feature review article, we will focus on the recent work on four different categories of graphene-based nanocomposite anodes by us and others: graphene-transitional metal oxide, graphene-Sn/Si/Ge, graphene-metal sulfide, and graphene-carbon nanotubes. For the supported materials on graphene, we will emphasize the non-zero dimensional (non-particle) morphologies such as two dimensional nanosheet/nanoplate and one dimensional nanorod/nanofibre/nanotube morphologies. The synthesis strategies and lithium-ion storage properties of these highlighted electrode morphologies are distinct from those of the commonly obtained zero dimensional nanoparticles. We aim to stress the importance of structure matching in the composites and their morphology-dependent lithium-storage properties and mechanisms.

Direct electrochemical synthesis of reduced graphene oxide (rGO)/copper composite films and their electrical/electroactive properties

Electrical contact materials with excellent performances are crucial for the development and safe use of electrical contacts in different applications. In our work, reduced graphene oxide (rGO)/copper (Cu) composite films, as potential electrical contact materials, have been synthesized on copper foil with one-step electrochemical reduction deposition method. Cyclic voltammetry (CV) was used to define the deposition conditions, and confocal Raman microscopy (CRM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize the chemical compositions, molecular and micro- and nano-structures of the composite films. Atomic force microscopy/scanning Kelvin probe force microscopy (AFM/SKPFM), conductive AFM (C-AFM) as well as impedance analysis were employed to evaluate the electroactive/electrical properties of the prepared composite films, respectively. The CRM and XPS results suggest that the rGO/Cu composite films can be synthesized through one-step electrochemical codeposition using suitable precursor solutions. Within a short deposition period, the growth of discrete nanograins in the composite film predominates, whereas pine-tree-leaf nanostructures are formed in the composite film when the deposition period is long, due to the chelating role of GO or rGO to regulate the growth rate of metallic copper nanograins. The electrical resistivity of the composite films is lower than the polished Cu foil and the electrodeposited Cu film, probably due to the higher conductivity (enhanced transfer of charge carriers) of the rGO incorporated in the composite films. The Volta potential variation in the rGO/Cu composite film is quite different from that in the electrodeposited Cu film. The electroactivity of the rGO/Cu composite films is higher than the electrodeposited Cu film, but lower than polished Cu foil, and the underlying mechanisms have been discussed.

Nitrogen-doped porous carbon/Co3O4 nanocomposites as anode materials for lithium-ion batteries

A simple and industrially scalable approach to prepare porous carbon (PC) with high surface areas as well as abundant nitrogen element as anode supporting materials for lithium-ion batteries (LIBs) was developed. Herein, the N-doped PC was prepared by carbonizing crawfish shell, which is a kind of food waste with abundant marine chitin as well as a naturally porous structure. The porous structure can be kept to form the N-doped PC in the pyrolysis process. The N-doped PC-Co3O4 nanocomposites were synthesized by loading Co3O4 on the N-doped PC as anode materials for LIBs. The resulting N-doped PC-Co3O4 nanocomposites release an initial discharge of 1223 mA h g(-1) at a current density of 100 mA g(-1) and still maintain a high reversible capacity of 1060 mA h g(-1) after 100 cycles, which is higher than that of individual N-doped PC or Co3O4. Particularly, the N-doped PC-Co3O4 nanocomposites can be prepared in a large yield with a low cost because the N-doped PC is derived from abundant natural waste resources, which makes it a promising anode material for LIBs.

Solution synthesis of metal oxides for electrochemical energy storage applications

This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices.

Raman enhancement by graphene-Ga2O3 2D bilayer film

2D β-Ga2O3 flakes on a continuous 2D graphene film were prepared by a one-step chemical vapor deposition on liquid gallium surface. The composite was characterized by optical microscopy, scanning electron microscopy, Raman spectroscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy (XPS). The experimental results indicate that Ga2O3 flakes grew on the surface of graphene film during the cooling process. In particular, tenfold enhancement of graphene Raman scattering signal was detected on Ga2O3 flakes, and XPS indicates the C-O bonding between graphene and Ga2O3. The mechanism of Raman enhancement was discussed. The 2D Ga2O3-2D graphene structure may possess potential applications.

Preparation via an electrochemical method of graphene films coated on both sides with NiO nanoparticles for use as high-performance lithium ion anodes

We report on a simple strategy for the direct synthesis of a thin film comprising interconnected NiO nanoparticles deposited on both sides of a graphene sheet via cathodic deposition. For the co-electrodeposition, graphene oxide (GO) is treated with water-soluble cationic poly(ethyleneimine) (PEI) which acts as a stabilizer and trapping agent to form complexes of GO and Ni2+. The positively charged complexes migrate toward the stainless steel substrate, resulting in the electrochemical deposition of PEI-modified GO/Ni(OH)2 at the electrode surface under an applied electric field. The as-synthesized film is then converted to graphene/NiO after annealing at 350 ° C. The interconnected NiO nanoparticles are uniformly deposited on both sides of the graphene surface, as evidenced by field emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectrometry. This graphene/NiO structure shows enhanced electrochemical performance with a large reversible capacity, good cyclic performance and improved electronic conductivity as an anode material for lithium ion batteries. A reversible capacity is retained above 586 mA h g−1 after 50 cycles. The findings reported herein suggest that this strategy can be effectively used to overcome a bottleneck problem associated with the electrochemical production of graphene/metal oxide films for lithium ion battery anodes.

Hybrid MnO2 film with agarose gel for enhancing the structural integrity of thin film supercapacitor electrodes

We report on the fabrication of a robust hybrid film containing MnO2 for achieving large areal capacitances. An agarose gel, as an ion-permeable and elastic layer coated on a current collector, plays a key role in stabilizing the deposited pseudocapacitive MnO2. Cyclic voltammetry and electrochemical impedance spectroscopy data indicate that the hybrid electrode is capable of exhibiting a high areal capacitance up to 52.55 mF cm(-2), with its superior structural integrity and adhesiveness to the current collector being maintained, even at a high MnO2 loading.

Free-standing and binder-free lithium-ion electrodes based on robust layered assembly of graphene and Co3O4 nanosheets

Free-standing and binder-free Co3O4/graphene films were fabricated through vacuum filtration and thermal treatment processes, in which sheet-like Co3O4 and graphene were assembled into a robust lamellar hierarchical structure via electrostatic interactions. The morphological compatibility coupled with strong interfacial interactions between Co3O4 and graphene significantly promoted the interfacial electron and lithium ion transport. When used as a binder-less and free-standing electrode for lithium-ion batteries, the hybrid film delivered a high specific capacity (~1400 mA h g(-1) at 100 mA g(-1) based on the total electrode weight), enhanced rate capability and excellent cyclic stability (~1200 mA h g(-1) at 200 mA g(-1) after 100 cycles). This effective strategy will provide new insight into the design and synthesis of many other composite electrodes for high-performance lithium-ion batteries.