Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

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Graphene-based composites

Graphene based materials: Past, present and future

Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

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Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

Three-dimensional (3D) N-doped graphene aerogel (N-GA)-supported Fe3O4 nanoparticles (Fe3O4/N-GAs) as efficient cathode catalysts for the oxygen reduction reaction (ORR) are reported. The graphene hybrids exhibit an interconnected macroporous framework of graphene sheets with uniform dispersion of Fe3O4 nanoparticles (NPs). In studying the effects of the carbon support on the Fe3O4 NPs for the ORR, we found that Fe3O4/N-GAs show a more positive onset potential, higher cathodic density, lower H2O2 yield, and higher electron transfer number for the ORR in alkaline media than Fe3O4 NPs supported on N-doped carbon black or N-doped graphene sheets, highlighting the importance of the 3D macropores and high specific surface area of the GA support for improving the ORR performance. Furthermore, Fe3O4/N-GAs show better durability than the commercial Pt/C catalyst.

3D Nitrogen-Doped Graphene Aerogel-Supported Fe3O4 Nanoparticles as Efficient Electrocatalysts for the Oxygen Reduction Reaction

Preparation of graphene by the rapid and mild thermal reduction of graphene oxide induced by microwaves

A 3D graphene architecture can be prepared via an in situ self-assembly of graphene prepared by a mild chemical reduction. Fe(3) O(4) nanoparticles are homogeneously dispersed into graphene oxide (GO) aqueous suspension and a 3D magnetic graphene/Fe(3) O(4) aerogel is prepared during the reduction of GO to graphene. This provides a general method to prepare 3D graphene/nanoparticle composites for a wide range of applications including catalysis and energy conversion.

Self‐Assembly and Embedding of Nanoparticles by In Situ Reduced Graphene for Preparation of a 3D Graphene/Nanoparticle Aerogel

Three-dimensional (3D) architectures of graphene are of interest in applications in electronics, catalysis devices, and sensors. However, it is still a challenge to fabricate macroscopic all-graphene 3D architectures under mild conditions. Here, a simple method for the preparation of 3D architectures of graphene is developed via the in situself-assembly of graphene prepared by mild chemical reduction at 95 °C under atmospheric pressure without stirring. No chemical or physical cross-linkers or high pressures are required. The reducing agents include NaHSO3, Na2S, Vitamin C, HI, and hydroquinone. Both graphene hydrogels and aerogels can be prepared by this method, and the shapes of the 3D architectures can be controlled by changing the type of reactor. The 3D architectures of graphene have low densities, high mechanical properties, thermal stability, high electrical conductivity, and high specific capacitance, which make them candidates for potential applications in supercapacitors, hydrogen storage and as supports for catalysts.

In situ self-assembly of mild chemical reduction graphene for three-dimensional architectures

Preparation of chitosan/graphene oxide composite film with enhanced mechanical strength in the wet state

Instead of hydrazine, a series of sulfur-containing compounds such as NaHSO3, Na2SO3, Na2S2O3, Na2S·9H2O, SOCl2, and SO2, were used as reducing agents to reduce graphene oxide to graphene. Fourier transform infrared spectrometry, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, elemental analysis, and thermogravimetric analysis confirmed the formation of graphene under chemical reduction at 95 °C. The results reveal that the reducing ability of NaHSO3 is comparable to that of hydrazine. This newly found reducing agent is of low toxicity and nonvolatile, which makes the reduction much safer than hydrazine. A possible mechanism of the reduction has been suggested. The electrical conductivity of the graphene paper prepared using a NaHSO3 reducing agent is found to be 6500 S m−1, while it is observed to be 5100 S m−1 for hydrazine-reduced graphene paper. These studies also confirmed that SOCl2 can be a good candidate as a reducing agent to compete with hydrazine.

Lifeng Yan

Papers

Preparation of graphene by the rapid and mild thermal reduction of graphene oxide induced by microwaves

Self‐Assembly and Embedding of Nanoparticles by In Situ Reduced Graphene for Preparation of a 3D Graphene/Nanoparticle Aerogel

In situ self-assembly of mild chemical reduction graphene for three-dimensional architectures

Preparation of chitosan/graphene oxide composite film with enhanced mechanical strength in the wet state

Chemical Reduction of Graphene Oxide to Graphene by Sulfur-Containing Compounds