Good dielectric performance and broadband dielectric polarization in Ag,Nb co-doped TiO2

Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO₂-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag⁺/Nb⁵⁺ co-doped (Ag_1/4Nb_3/4)_xTi_1−xO₂ (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 10³ and 1.6 × 10⁴ at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.     

Microstructure,mechanical, tribological,and oxidizing properties of AlCrSiN/AlCrVN/AlCrNbN multilayer coatings with different modulated thicknesses

Multilayer structure design is one of the most promising methods for improving the comprehensive performance of AlCrN-based hard coatings applied to cutting tools. In this study, four types of AlCrSiN/AlCrVN/AlCrNbN multilayer coatings, with different modulated thicknesses, were deposited to investigate their microstructure, mechanical, tribological, and oxidizing properties. All multilayer coatings exhibited grain growth along the crystallographic plane of (200) with a NaCl-type face-centered cubic (FCC) structure. The results show that, as the modulation thickness decreases from ～35 nm to ～10 nm, (1) the grain refinement effect is increasingly evident; (2) all multilayer coatings show a hardness of >30 GPa and an elastic modulus of >300 GPa. Both the ability to resist elastic strain to failure and the plastic deformation of multilayer coatings increase. In addition, their resistance to cracking reduces; (3) the wear rates of these multilayer coatings reduce successively from 1.78 × 10^?16 m³ N^?1 m^?1 to 7.7 × 10^?17 m³ N^?1 m^?1. This is attributed to an increase in self-lubricating VO_x and a decrease in adhesives from the counterparts; (4) the best high-temperature oxidation resistance was obtained for the multilayer coating with a modulated thickness of ～15 nm.     

Thermomechanical stability and inelastic energy dissipation as durability criteria for fuel cell gas diffusion media with pre-assembly effects

In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load.     

Bovidae-based gelatin: Extractions method,physicochemical and functional properties,applications, and future trends

Gelatin is one of the most important multifunctional biopolymers and is widely used as an essential ingredient in food, pharmaceutical, and cosmetics. Porcine gelatin is regarded as the leading source of gelatin globally then followed by bovine gelatin. Porcine sources are favored over other sources since they are less expensive. However, porcine gelatin is religiously prohibited to be consumed by Muslims and the Jewish community. It is predicted that the global demand for gelatin will increase significantly in the future. Therefore, a sustainable source of gelatin with efficient production and free of disease transmission must be developed. The highest quality of Bovidae-based gelatin (BG) was acquired through alkaline pretreatment, which displayed excellent physicochemical and rheological properties. The utilization of mammalian- and plant-based enzyme significantly increased the gelatin yield. The emulsifying and foaming properties of BG also showed good stability when incorporated into food and pharmaceutical products. Manipulation of extraction conditions has enabled the development of custom-made gelatin with desired properties. This review highlighted the various modifications of extraction and processing methods to improve the physicochemical and functional properties of Bovidae-based gelatin. An in-depth analysis of the crucial stage of collagen breakdown is also discussed, which involved acid, alkaline, and enzyme pretreatment, respectively. In addition, the unique characteristics and primary qualities of BG including protein content, amphoteric property, gel strength, emulsifying and viscosity properties, and foaming ability were presented. Finally, the applications and prospects of BG as the preferred gelatin source globally were outlined.     

Theoretical prediction of structure,electronic and optical properties of VH2 hydrogen storage material

The vanadium hydrides have better hydrogen storage capacity in comparison to the other metal hydrides. Although the structure of VH₂ hydride has been reported, the structural stability, electronic and optical properties of VH₂ hydride are unclear. To solve these problems, we apply the first-principles method to study the structural stability, electronic and optical properties of VH₂ hydrides. Similar to the metal dihydrides, four possible VH₂ hydrides such as the cubic (Fm-3m), tetragonal (I4/mmm), tetragonal (P4₂/mnm) and orthorhombic (Pnma) are designed. The result shows that the cubic VH₂ hydride is a thermodynamic and dynamical stability. In particular, the tetragonal (I4/mmm) and the orthorhombic (Pnma) VH₂ hydrides are firstly predicted. It is found that these VH₂ hydrides show metallic behavior. The electronic interaction of V (d-state)-H (s-state) is beneficial to improve the hydrogen storage in VH₂ hydride. In addition, the formation of V–H bond can improve the structural stability of VH₂ hydride. Based on the analysis of optical properties, it is found that all VH₂ hydrides show the ultraviolet response. Compared to the tetragonal and orthorhombic VH₂ hydrides, the cubic VH₂ hydride has better storage optical properties. Therefore, we believe that the VH₂ hydride is a promising hydrogen storage material.     

Density functional theory study of the hydrogen evolution reaction in haeckelite boron nitride quantum dots

To satisfy arising energy needs and to handle the forthcoming worldwide climate transformation, the major research attention has been drawn to environmentally friendly, renewable and abundant energy resources. Hydrogen plays an ideal and significant role is such resources, due to its non-carbon based energy and production through clean energy. In this work, we have explored catalytic activity of a newly predicted haeckelite boron nitride quantum dot (haeck-BNQD), constructed from the infinite BN sheet, for its utilization in hydrogen production. Density functional theory calculations are employed to investigate geometry optimization, electronic and adsorption mechanism of haeck-BNQD using Gaussian16 package, employing the hybrid B3LYP and wB97XD functionals, along with 6–31G(d,p) basis set. A number of physical quantities such as HOMO/LUMO energies, density of states, hydrogen atom adsorption energies, Mulliken populations, Gibbs free energy, work functions, overpotentials, etc., have been computed and analysed in the context of the catalytic performance of haeck-BNQD for the hydrogen-evolution reaction (HER). Based on our calculations, we predict that the best catalytic performance will be obtained for H adsorption on top of the squares or the octagons of haeck-BNQD. We hope that our prediction of most active catalytic sites on haeck-BNQD for HER will be put to test in future experiments.     

A review of hydrogen production processes by photocatalytic water splitting – From atomistic catalysis design to optimal reactor engineering

‘Renewable energy is an essential part of our strategy of decarbonization, decentralization, as well as digitalization of energy.’ – Isabelle Kocher.Current climate, health and economic condition of our globe demands the use of renewable energy and the development of novel materials for the efficient generation, storage and transportation of renewable energy. Hydrogen has been recognised as one of the most prominent carriers and green energy source with challenging storage, enabling decarbonization. Photocatalytic H₂ (green hydrogen) production processes are targeting the intensification of separated solar energy harvesting, storage and electrolysis, conventionally yielding O₂/H₂. While catalysis is being investigated extensively, little is done on bridging the gap, related to reactor unit design, optimisation and scaling, be it that of material or of operation. Herein, metals, oxides, perovskites, nitrides, carbides, sulphides, phosphides, 2D structures and heterojunctions are compared in terms of parameters, allowing for efficiency, thermodynamics or kinetics structure–activity relationships, such as the solar-to-hydrogen (STH). Moreover, prominent pilot systems are presented summarily.     

New horizon in mechanochemistry—high-temperature,high-pressure mechanical synthesis in a planetary ball mill—with magnesium hydride synthesis as an example

A new route of materials synthesis, namely, high-temperature, high-pressure reactive planetary ball milling (HTPRM), is presented. HTPRM allows for the mechanosynthesis of materials at fully controlled temperatures of up to 450 °C and pressures of up to 100 bar of hydrogen. As an example of this application, a successful synthesis of magnesium hydride is presented. The synthesis was performed at controlled temperatures (room temperature (RT), 100, 150, 200, 250, 300, and 325 °C) while milling in a planetary ball mill under hydrogen pressure ($>$50 bar). Very mild milling conditions (250 rpm) were applied for a total milling time of 2 h, and a milling vial with a relatively small diameter (φ = 53 mm, V = ～0.06 dm³) was used. The effect of different temperatures on the synthesis kinetics and outcome were examined. The particle morphology, phase composition, reaction yield, and particle size were measured and analysed by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC) techniques. The obtained results showed that increasing the temperature of the process significantly improved the reaction rate, which suggested the great potential of this technique for the mechanochemical synthesis of materials.     

Recent insights in synthesis and energy storage applications of porous carbon derived from biomass waste: A review

In the last few decades, global warming, environmental pollution, and an energy shortage of fossil fuel may cause a severe economic crisis and health threats. Storage, conversion, and application of regenerable and dispersive energy would be a promising solution to release this crisis. The development of porous carbon materials from regenerated biomass are competent methods to store energy with high performance and limited environmental damages. In this regard, bio-carbon with abundant surface functional groups and an easily tunable three-dimensional porous structure may be a potential candidate as a sustainable and green carbon material. Up to now, although some literature has screened the biomass source, reaction temperature, and activator dosage during thermochemical synthesis, a comprehensive evaluation and a detailed discussion of the relationship between raw materials, preparation methods, and the structural and chemical properties of carbon materials are still lacking. Hence, in this review, we first assess the recent advancements in carbonization and activation process of biomass with different compositions and the activity performance in various energy storage applications including supercapacitors, lithium-ion batteries, and hydrogen storage, highlighting the mechanisms and open questions in current energy society. After that, the connections between preparation methods and porous carbon properties including specific surface area, pore volume, and surface chemistry are reviewed in detail. Importantly, we discuss the relationship between the pore structure of prepared porous carbon with surface functional groups, and the energy storage performance in various energy storage fields for different biomass sources and thermal conversion methods. Finally, the conclusion and prospective are concluded to give an outlook for the development of biomass carbon materials, and energy storage applications technologies. This review demonstrates significant potentials for energy applications of biomass materials, and it is expected to inspire new discoveries to promote practical applications of biomass materials in more energy storage and conversion fields.