Increased energy consumption stimulates the development of various energy types. As a result, the storage of these different types of energy becomes a key issue. Supercapacitors, as one important ...energy storage device, have gained much attention and owned a wide range of applications by taking advantages of micro-size, lightweight, high power density and long cycle life. From this perspective, numerous studies, especially on electrode materials, have been reported and great progress in the advancement in both the fundamental and applied fields of supercapacitor has been achieved. Herein, a review of recent progress in carbon materials for supercapacitor electrodes is presented. First, the two mechanisms of supercapacitors are briefly introduced. Then, research on carbon-based material electrodes for supercapacitor in recent years is summarized, including different dimensional carbon-based materials and biomass-derived carbon materials. The characteristics and fabrication methods of these materials and their performance as capacitor electrodes are discussed. On the basis of these materials, many supercapacitor devices have been developed. Therefore, in the third part, the supercapacitor devices based on these carbon materials are summarized. A brief overview of two types of conventional supercapacitor according to the charge storage mechanism is compiled, including their development process, the merits or withdraws, and the principle of expanding the potential range. Additionally, another fast-developed capacitor, hybrid ion capacitors as a good compromise between battery and supercapacitor are also discussed. Finally, the future aspects and challenges on the carbon-based materials as supercapacitor electrodes are proposed.
This article is devoted to the study of the efficiency of thermal annealing of nanostructures for phase transformations of the FeCo – Fe
2
CoO
4
/Co
3
O
4
-spinel type, as well as the subsequent ...application of the obtained nanotubes as a basis for anode materials of lithium-ion batteries. The choice of these types of nanotubes for use as a basis for anode materials is due to their structure, as well as the great potential of using spinel structures in this area, interest in which is manifested due to the possibility of accelerating lithiation processes and long-term preservation of the specific capacity of batteries. During the study, it was found that for spinel structures, the formation of oxide growths on the surface of nanotubes, the presence of which is associated with oxidative processes during annealing, is observed. Testing the applicability of these structures as anode materials showed that the formation of oxide spinel structures of type Fe
2
CoO
4
/Co
3
O
4
leads to an increase in the number of cycles by 1.5–1.7 times compared to the original nanotubes. The efficiency of increasing the lifetime of anode materials is due to an increase in resistance to degradation of Fe
2
CoO
4
/Co
3
O
4
structures, due to the formation of oxide phases, leading to an acceleration of lithation processes.
There has been much effort to provide eco-friendly and biodegradable materials for the next generation of composite products owing to global environmental concerns and increased awareness of ...renewable green resources. An increase in the use of natural materials in composites has led to a reduction in greenhouse gas emissions and carbon footprint of composites. In addition to the benefits obtained from green materials, there are some challenges in working with them, such as poor compatibility between the reinforcing natural fiber and matrix and the relatively high moisture absorption of natural fibers. Green composites can be a suitable alternative for petroleum-based materials. However, before this can be accomplished, there are a number of issues that need to be addressed, including poor interfacial adhesion between the matrix and natural fibers, moisture absorption, poor fire resistance, low impact strength, and low durability. Several researchers have studied the properties of natural fiber composites. These investigations have resulted in the development of several procedures for modifying natural fibers and resins. To address the increasing demand to use eco-friendly materials in different applications, an up-do-date review on natural fiber and resin types and sources, modification and processing techniques, physical and mechanical behaviors, applications, life-cycle assessment, and other properties of green composites is required to provide a better understanding of the behavior of green composites. This paper presents such a review based on 322 studies published since 1978.
In the present review, the recent progress in describing the intricacies of mechanical and thermal properties of all types of graphene- and modified graphene-based polymer nanocomposites has been ...comprehensively examined. The effectiveness of microscopy bouquet for the intrinsic characterization of graphene family and their composites was clearly demonstrated in this research. Furthermore, the utility of the dynamic mechanical analysis and thermo-gravimetric analysis employed for thermal characterization that has been reported by various researchers was exhaustively analyzed in this paper. This research primarily focused on the analyses of several good articles concerned with hybrid graphene composites and the synergetic effect of graphene with other nanofiller to assess its effect on the mechanical properties of its corresponding composites. Such systematic analysis of previous literatures imparted a direction to the researchers about the solution of improved interfacial properties as well as the enhanced dispersion into the vicinity of the matrix. This current research has suggested that the presence of the graphene filler even at very low loadings has shown considerable improvement in the overall mechanical properties of graphene. Further studies to optimize the value of the filler need to be addressed in order to gain complete understanding of the properties of graphene. The potential applications, current challenges, and future perspectives pertaining to these nanocomposites were elaborately discussed in the current study with regard to the multi-scale capabilities and promising developments of the graphene-family-based nanocomposites materials.
We review some of the factors that influence the hardness of polycrystalline materials with grain sizes less than 1 µm. The fundamental physical mechanisms that govern the hardness of nanocrystalline ...materials are discussed. The recently proposed dislocation curvature model for grain size-dependent strengthening and the 60-year-old Hall–Petch relationship are compared. For grains less than 30 nm in size, there is evidence for a transition from dislocation-based plasticity to grain boundary sliding, rotation, or diffusion as the main mechanism responsible for hardness. The evidence surrounding the inverse Hall–Petch phenomenon is found to be inconclusive due to processing artefacts, grain growth effects, and errors associated with the conversion of hardness to yield strength in nanocrystalline materials.
Thermal modification is a well-established commercial technology for improving the dimensional stability and durability of timber. Numerous reviews of thermally modified timber (TMT) are to be found ...in the scientific literature, but until now a review of the influence of cell wall moisture content during the modification process on the properties of TMT has been lacking. This paper reviews the current state of knowledge regarding the hygroscopic and dimensional behaviour of TMT modified under dry (cell wall at nearly zero moisture content) and wet (cell wall contains moisture) conditions. After an overview of the topic area, the review explores the literature on the thermal degradation of the polysaccharidic and lignin components of the cell wall, as well as the role of extractives. The properties of TMT modified under wet and dry conditions are compared including mass loss, hygroscopic behaviour and dimensional stability. The role of hydroxyl groups in determining the hygroscopicity is discussed, as well as the importance of considering the mobility of the cell wall polymers and crosslinking when interpreting sorption behaviour. TMT produced under wet processing conditions exhibits behaviour that changes when the wood is subjected to water leaching post-treatment, which includes further weight loss, changes in sorption behaviour and dimensional stability, but without any further change in accessible hydroxyl (OH) content. This raises serious questions regarding the role that OH groups play in sorption behaviour.
Graphical abstract
Thermoelectric materials are capable of converting heat and electricity to each other. Thermoelectric devices can be miniaturized and highly integrated with existing semiconductor chip systems with ...microgenerators or microrefrigerators. After years of research and accumulation, BiTe series, SnSe series, CuSe series, half-Heusler series, multicomponent oxides series, organic–inorganic composites series, and GeTe/PbTe series have been found to have excellent thermoelectric properties. According to theoretical calculation, when the diameter of Bi
2
Te
3
nanowires is 5 Å, the ZT value reaches 14, and graphdiyne has a ZT value of 4.8 at 300 K. Experimental measurements revealed that the ZT value of n-type SnSe reached 2.8. This review would focus on the updated experimental and theoretical achievements of seven kinds of materials, including BiTe series, SnSe series, CuSe series, multicomponent oxides, half-Heusler alloys, organic–inorganic composites, and GeTe/PbTe series. The preparation method, microstructure characteristics, device structure, and thermoelectric properties of each material will be described in detail. By analyzing the performance of these materials, three possible development directions are put forward for how to further improve the thermoelectric properties of materials.
Depending on their structure and order (individual, films, bundled, buckypapers, etc.), carbon nanotubes (CNTs) demonstrate different values of thermal conductivity, from the level of thermal ...insulation with the thermal conductivity of 0.1 W/mK to such high values as 6600 W/mK. This review article concentrates on analyzing the articles on thermal conductivity of CNT networks. It describes various measurement methods, such as the 3-ω method, bolometric, steady-state method and their variations, hot-disk method, laser flash analysis, thermoreflectance method and Raman spectroscopy, and summarizes the results obtained using those techniques. The article provides the main factors affecting the value of thermal conductivity, such as CNT density, number of defects in their structure, CNT ordering within arrays, direction of measurement in relation to their length, temperature of measurement and type of CNTs. The practical methods of using CNT networks and the potential directions of future research in that scope were also described.
Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and ...cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.
The structural, electronic, elastic, magnetic, and thermodynamic properties of two new Heusler alloys Rh
2
MnZ (Z = Zr, Hf) are studied based on the first principal calculation using the scheme of ...the generalized gradient approximation (GGA) of density function theory. The investigation was carried out in ferromagnetic (FM), anti-ferromagnetic (AFM), and the non-magnetic (NM) phases of the Cu2MnAl-type structure (regular structure) and Hg
2
CuTi-type-structure (inverse structure). Both alloys were found to be more stable in the ferromagnetic phase of the Cu2MnAl-type structure. The equilibrium lattice parameter in this structure is equal to 6.39 Ǻ for Rh
2
MnZr and 6.35 Ǻ for Rh
2
MnHf. The electronic properties reveled the metallic nature of the Heusler Rh
2
MnZ (Z = Zr, Hf) alloys. The interpretation of the elastic properties confirmed the elastic stability of the two alloys in the studied structure with a good agreement between the resulting bulk modulus from the structural properties and that of resulting from the elastic properties. Other elastic parameters such as modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio (
ν
) and Pugh’s ratio B/G, and the Zener anisotropy parameter A showed that the Rh
2
MnZ (Z = Zr, Hf) alloys are slightly deformed. They show high rigidity, anisotropic, and little deformation and behave in ductile way. The magnetic properties confirmed the ferromagnetic state of both compounds with computed total magnetic moment equal to 4.76 μ
B
for Rh2MnZr and 4.60 μ
B
for Rh
2
MnHf. The thermodynamic parameters were evaluated with various temperatures between 0 and 1200 K and a pressure from 0 to 50 GPa using the quasi-harmonic Debye model.
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