No abstract

Zinc-air batteries have attracted much attention and received revived research efforts recently due to their high energy density, which makes them a promising candidate for emerging mobile and electronic applications. Besides their high energy density, they also demonstrate other desirable characteristics, such as abundant raw materials, environmental friendliness, safety, and low cost. Here, the reaction mechanism of electrically rechargeable zinc-air batteries is discussed, different battery configurations are compared, and an in depth discussion is offered of the major issues that affect individual cellular components, along with respective strategies to alleviate these issues to enhance battery performance. Additionally, a section dedicated to battery-testing techniques and corresponding recommendations for best practices are included. Finally, a general perspective on the current limitations, recent application-targeted developments, and recommended future research directions to prolong the lifespan of electrically rechargeable zinc-air batteries is provided.

Natural graphite was intercalated, thermally exfoliated, and dispersed in acetone to prepare graphite nanoplatelets (GNPs, G n ) of controlled aspect ratio. Thermal conductivity measurements indicate that few graphene layer G n , where n ∼ 4, with a thickness of ∼2 nm function as a very efficient filler for epoxy composites. When embedded in an epoxy matrix, the G4 GNPs provide a thermal conductivity enhancement of more than 3000% (loading of ∼25 vol %), and a thermal conductivity κ = 6.44 W/mK, which surpasses the performance of conventional fillers that require a loading of ∼70 vol % to achieve these values. We attribute the outstanding thermal properties of this material to a favorable combination of the high aspect ratio, two-dimensional geometry, stiffness, and low thermal interface resistance of the GNPs.

This paper gives a comprehensive review about the most recent progress in synthesis, characterization, fundamental understanding, and the performance of graphene and graphene oxide sponges. Practical applications are considered including use in composite materials, as the electrode materials for electrochemical sensors, as absorbers for both gases and liquids, and as electrode materials for devices involved in electrochemical energy storage and conversion. Several advantages of both graphene and graphene oxide sponges such as three dimensional graphene networks, high surface area, high electro/ thermo conductivities, high chemical/electrochemical stability, high flexibility and elasticity, and extremely high surface hydrophobicity are emphasized. To facilitate further research and development, the technical challenges are discussed, and several future research directions are also suggested in this paper. Broader contextAdvanced graphene materials residing at the frontier of scientic research offer immense potential for overcoming the challenges related to the performance, functionality and durability of key functional materials' in the elds of life science, energy, and the environment. Future demand necessitates advanced processing methods be developed that can mass produce high quality, two-dimensional graphene sheets while overcoming the issues of poor dispersion and restacking with large size-scale deployment of two-dimensional graphene sheets. These issues, along with graphene sheet defects and multilayer thicknesses prevent the full realization of graphene's high potential, including electronic properties and high surface area. Three-dimensional arrangements have been recently able to address these limitations, by creating sponge-like low density materials with a long list of benecial properties including: macroscale size, high accessible surface area, less restacking, highly-interconnected microstructure, high strength and exibility, fast ion transport and electron conductivity. This review is intended to address the continued developments and challenges with a wide scope of interest, highlighting fundamental understanding of the synthesis and characterization procedures, future outlook, as well as an in-depth discussion of application areas reporting high performance in recent publications. The outstanding potential of these materials has enabled signicant enhancements for numerous important applications such as electrochemical energy storage and conversion, absorption, sensing, catalysis, transistors and polymer composites.

The increased heat generated in high density electronics has intensified the search for advanced thermal interface materials (TIMs) and prompted fundamental studies at the nanoscale level to develop filler materials with enhanced thermal performance. [1][2][3][4] Single-walled carbon nanotubes (SWNTs) considerably improve the heat transport in polymer composites as a result of their one-dimensional (1D) structure, high thermal conductivity and high aspect ratio. [5][6][7][8][9][10][11][12] Recently, two-dimensional (2D) nanostructures such as graphite nanoplatelets (GNPs), have emerged as a promising filler in polymer matrices [13][14][15][16][17][18][19] and it has been shown that they provide even higher thermal conductivity enhancement than SWNTs. [16] In this study we combine 1D-SWNTs and 2D-GNPs to prepare a series of hybrid graphitic nanofillers and we observe a synergistic effect between the GNPs and SWNTs in the enhancement of the thermal conductivity of epoxy composites to the point that at certain filler loadings the hybrid composition outperforms composites utilizing pure GNP or SWNT fillers. The increased thermal conductivity is ascribed to the formation of a more efficient percolating nanoparticle network with significantly reduced thermal interface resistances. The idea of using a hybrid filler comprised of two or more traditional filler materials has already been explored in the literature and it has been demonstrated that improved composite performance can be achieved by combining the advantages of each filler. [20,21] Commercially available thermal greases and adhesives often utilize several components to achieve the desired combination of thermal and electrical conductivities, viscosity and low coefficient of thermal expansion. In our study, we utilize two different nanostructured graphitic fillers for incorporation into epoxy resin: purified SWNTs and graphite nanoplatelets (GNPs) comprised of few graphene layer G n , where n $ 4. The SWNT component of the hybrid filler is electric arc produced purified SWNTs with a typical length of 0.3-1.0 mm and an average diameter of 1.4 nm. The purification process [22] leaves the SWNTs ends and side-walls functionalized with carboxylic acid groups and this facilitates their homogeneous dispersion into the polymer matrix. In addition, the epoxy curing process is accompanied by a cross-linking reaction between the carboxylic acid groups of the SWNTs and the epoxy groups of the polymer, [23] thus improving the integration of SWNTs into the polymer matrix. GNPs are typically prepared by intercalation and exfoliation of graphite; [24][25][26][27][28][29] and by control of the exfoliation conditions we were able to obtain GNPs comprised of 2 to 8 graphene layers with a lateral dimension of 200-1000 nm and an aspect ratio in the range of 50 to 300. [16] This was achieved by thermal shock exfoliation of natural graphite flakes at 800 8C [25,26] followed by high shear mixing and sonication in order to separate the exfoliated graphite flakes into nanoplatelets.[...