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The aluminum-water system is a promising propellant due to high energy and low signal characteristics, and the gel form is easier to store and utilize. In this work, hydrogels of water and aluminum particles were prepared using the low-molecular-weight gellant agarose. The various physical properties of gel systems, including the water loss rate, phase transition temperature, and centrifugal stability at different gellant and aluminum contents, were examined. Rheological properties were assessed through shear thinning tests, thixotropy tests, strain sweep analysis, and frequency sweep experiments. The microstructure of the gel was obtained through scanning electron microscopy images. The results show that the aluminum-hydrogel network structure is composed of micron-scale aluminum and agarose nanosheets, and the unique micro-nanostructure endows the gel with excellent mechanical strength and thermal stability, which improve with increasing gellant and aluminum contents. Notably, the gel with 2% agarose and 20% aluminum had the best performance; the storage modulus reached 90647 Pa, which was within the linear viscoelastic region, and the maximum withstand pressure was 111.2 kPa, which was 118.8% greater than that of the pure hydrogel. Additionally, the gel demonstrates remarkable shear thinning behavior and can undergo gel-sol transformation upon shearing or heating to exceeding 114 °C. [ABSTRACT FROM AUTHOR]

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Decalin is considered as an important compound of high-energy-density endothermic fuel, which is an ideal on-board coolant for thermal management of advanced aircraft. However, decalin contains two isomers with a tunable composition, and their effects on the pyrolysis performance, such as the heat sink and coking tendency have not been demonstrated. Herein, we investigated the pyrolysis of decalin isomers, i.e., cis-decalin, trans-decalin and their mixtures (denoted as mix-decalin), in order to clarify the effects of the cis-/trans-structures on the pyrolysis performance of decalin fuels. The pyrolysis results confirmed that conversion of the tested fuels (600–725 °C, 4 MPa) decreased in the order cis-decalin > mix-decalin > trans-decalin. Detailed analyses of the pyrolysis products were used to compare the product distributions from cis-decalin, mix-decalin and trans-decalin, and the yields of some typical components (such as cyclohexene, 1-methylcyclohexene, benzene and toluene) showed significant differences, which could be ascribed to deeper cracking of cis-decalin. Additionally, the heat sinks and coking tendencies of the decalins decreased in the order cis-decalin > mix-decalin > trans-decalin. This work demonstrates the relationship between the cis/trans structures and the pyrolysis performance of decalin, which provides a better understanding of the structure-activity relationships of endothermic hydrocarbon fuels. [ABSTRACT FROM AUTHOR]

Water electrolysis, a process for producing green hydrogen from renewable energy, plays a crucial role in the transition toward a sustainable energy landscape and the realization of the hydrogen economy. Oxygen evolution reaction (OER) is a critical step in water electrolysis and is often limited by its slow kinetics. Two main mechanisms, namely the adsorbate evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM), are commonly considered in the context of OER. However, designing efficient catalysts based on either the AEM or the LOM remains a topic of debate, and there is no consensus on whether activity and stability are directly related to a certain mechanism. Considering the above, we discuss the characteristics, advantages, and disadvantages of AEM and LOM. Additionally, we provide insights on leveraging the LOM to develop highly active and stable OER catalysts in future. For instance, it is essential to accurately differentiate between reversible and irreversible lattice oxygen redox reactions to elucidate the LOM. Furthermore, we discuss strategies for effectively activating lattice oxygen to achieve controllable steady-state exchange between lattice oxygen and an electrolyte (OH− or H2O). Additionally, we discuss the use of in situ characterization techniques and theoretical calculations as promising avenues for further elucidating the LOM. [ABSTRACT FROM AUTHOR]

Surface reconstruction generates real active species in electrochemical conditions; rational regulating reconstruction in a targeted manner is the key for constructing highly active catalyst. Herein, we use the high-valence Mo modulated orthorhombic Pr3Ir1−xMoxO7 as model to activate lattice oxygen and cations, achieving directional and accelerated surface reconstruction to produce self-terminated Ir‒Obri‒Mo (Obri represents the bridge oxygen) active species that is highly active for acidic water oxidation. The doped Mo not only contributes to accelerated surface reconstruction due to optimized Ir‒O covalency and more prone dissolution of Pr, but also affords the improved durability resulted from Mo-buffered charge compensation, thereby preventing fierce Ir dissolution and excessive lattice oxygen loss. As such, Ir‒Obri‒Mo species could be directionally generated, in which the strong Brønsted acidity of Obri induced by remaining Mo assists with the facilitated deprotonation of oxo intermediates, following bridging-oxygen-assisted deprotonation pathway. Consequently, the optimal catalyst exhibits the best activity with an overpotential of 259 mV to reach 10 mA cmgeo−2, 50 mV lower than undoped counterpart, and shows improved stability for over 200 h. This work provides a strategy of directional surface reconstruction to constructing strong Brønsted acid sites in IrOx species, demonstrating the perspective of targeted electrocatalyst fabrication under in situ realistic reaction conditions. Regulating surface reconstruction is an important way to construct highly active catalyst for acidic water oxidation. Here the authors report high-valence Mo accelerates surface reconstruction of orthorhombic Pr3Ir1−xMoxO7 by activating lattice oxygen and cations, forming highly active and self-terminated Ir‒Obri‒Mo species with strong Brønsted acidity for acidic oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Electrocatalytic water splitting is limited by kinetics-sluggish oxygen evolution, in which the activity of catalysts depends on their electronic structure. However, the influence of electron spin polarization on catalytic activity is ambiguous. Herein, we successfully regulate the spin polarization of Co3O4 catalysts by tuning the concentration of cobalt defects from 0.8 to 14.5%. X-ray absorption spectroscopy spectra and density functional theory calculations confirm that the spin polarization of Co3O4 is positively correlated with the concentration of cobalt defects. Importantly, the enhanced spin polarization can increase hydroxyl group absorption to significantly decrease the Gibbs free energy change value of the OER rate-determining step and regulate the spin polarization of oxygen species through a spin electron-exchange process to easily produce triplet-state O2, which can obviously increase electrocatalytic OER activity. In specific, Co3O4-50 with 14.5% cobalt defects exhibits the highest spin polarization and shows the best normalized OER activity. This work provides an important strategy to increase the water splitting activity of electrocatalysts via the rational regulation of electron spin polarization. [ABSTRACT FROM AUTHOR]

With the increasing demand for high-performance and safe fuels in aerospace propulsion systems, gelled fuels have attracted increasing attention. Because of their unique structure, gelled fuels exhibit the advantages of both solid and liquid fuels, such as high energy density, controllable thrust and storage safety. This review provides an overview on design, preparation and performance characterization of gelled fuels. The composition, preparation process and gelation mechanism of gelled high-energy-density fuels are described. Considering these aspects, the rheology and flow behavior of gelled fuels is summarized in terms of the shear thinning property, dynamic viscoelasticity and thixotropy. Moreover, the progress of atomization of gelled fuels is reviewed with a focus on the effect of atomizing nozzles. In addition, the experiments and theoretical models of single droplet combustion and combustor combustion are described. Finally, research directions for the development and application of gelled fuels are suggested. [ABSTRACT FROM AUTHOR]

Aerospace aircraft has significantly improved the life quality of human beings and extended the capability of space explosion since its appearance in 1903, in which liquid propellants or fuels provide the key power source. For jet fuels, its property of energy density plays an important role in determining the flight range, load, and performance of the aircraft. Therefore, the design and fabrication of high-energy-density (HED) fuels attract more and more attention from researchers all over the world. Herein, we briefly introduce the development of liquid jet fuels and HED fuels and demonstrate the future development of HED fuels. To further improve the energy density of fuel, the approaches of design and construction of multi-cyclic and stained molecule structures are proposed. To break through the density limit of hydrocarbon fuels, the addition of energetic nanoparticles in HED fuels to produce nanofluid or gelled fuels may provide a facile and effective method to significantly increase the energy density. This work provides the perspective for the development of HED fuels for advanced aircrafts. [ABSTRACT FROM AUTHOR]

High-energy-density liquid hydrocarbon fuels are generally synthesized using various chemical reactions to improve the performance (e.g., range, load, speed) of aerospace vehicles. Compared with conventional fuels, such as aviation kerosene and rocket kerosene, these liquid hydrocarbon fuels possess the advantages of high-energy-density and high volumetric calorific value; therefore, the fuels have important application value. The photocatalytic process has shown great potential for the synthesis of a diverse range of fuels on account of its unique properties, which include good efficiency, clean atomic economy, and low energy consumption. These characteristics have led to the emergence of the photocatalytic process as a promising complement and alternative to traditional thermocatalytic reactions for fuel synthesis. Extensive effort has been made toward the construction of catalysts for the multiple photocatalytic syntheses of high-energy-density fuels. In this review, we aim to summarize the research progress on the photocatalytic synthesis of high-energy-density fuel by using homogeneous and heterogeneous catalytic reactions. Specifically, the synthesis routes, catalysts, mechanistic features, and future challenges for the photocatalytic synthesis of high-energy-density fuel are described in detail. The highlights of this review not only promote the development of the photocatalytic synthesis of high-energy-density fuel but also expand the applications of photocatalysis to other fields. [ABSTRACT FROM AUTHOR]

The development of advanced air transportation has raised new demands for high-performance liquid hydrocarbon fuels. However, the measurement of fuel properties is time-consuming, cost-intensive, and limited to the operating conditions. The physicochemical properties of aerospace fuels are directly influenced by chemical composition. Thus, a thorough investigation should be conducted on the inherent relationship between fuel properties and composition for the design and synthesis of high-grade fuels and the prediction of fuel properties in the future. This work summarized the effects of fuel composition and hydrocarbon molecular structure on the fuel physicochemical properties, including density, net heat of combustion (NHOC), low-temperature fluidity (viscosity and freezing point), flash point, and thermal-oxidative stability. Several correlations and predictions of fuel properties from chemical composition were reviewed. Additionally, we correlated the fuel properties with hydrogen/carbon molar ratios (nH/C) and molecular weight (M). The results from the least-square method implicate that the coupling of H/C molar ratio and M is suitable for the estimation of density, NHOC, viscosity and effectiveness for the design, manufacture, and evaluation of aviation hydrocarbon fuels. [ABSTRACT FROM AUTHOR]

Thermal oxidation stability is an important parameter for jet fuel practical application. In this work, in order to evaluate the influence of deoxygenation on fuel stability, samples of typical fuels (JP-10 and RP-3) were subjected to deoxygenation by nitrogen purge and then subjected to accelerated thermal oxidation (180°C, 200°C, and 220°C). The parameters of hydroperoxide number, total acid number, size distribution of insoluble oxidation products, and concentration of remaining antioxidant (butylated hydroxytoluene, MIT) were monitored and analyzed. The results show that deoxygenation and thermal oxidation have very little influence on the fuel physical properties (density, net heating value, and kinematic viscosity). However, deoxygenation significantly reduces hydroperoxide number, total acid number, and remaining BHT concentration in the fuel after accelerated oxidation. Moreover, the deoxygenation treatment also inhibits the formation of soluble macromolecular oxidatively reactive species (SMORS) and insoluble oxidation products such as gums and deposits. [ABSTRACT FROM AUTHOR]

Photocatalysis has been regarded as a promising strategy for hydrogen production and high-value-added chemicals synthesis, in which the activity of photocatalyst depends significantly on their electronic structures, however the effect of electron spin polarization has been rarely considered. Here we report a controllable method to manipulate its electron spin polarization by tuning the concentration of Ti vacancies. The characterizations confirm the emergence of spatial spin polarization among Ti-defected TiO2, which promotes the efficiency of charge separation and surface reaction via the parallel alignment of electron spin orientation. Specifically, Ti0.936O2, possessing intensive spin polarization, performs 20-fold increased photocatalytic hydrogen evolution and 8-fold increased phenol photodegradation rates, compared with stoichiometric TiO2. Notably, we further observed the positive effect of external magnetic fields on photocatalytic activity of spin-polarized TiO2, attributed to the enhanced electron-spin parallel alignment. This work may create the opportunity for tailoring the spin-dependent electronic structures in metal oxides. Photocatalyst activity depends significantly on the material's electronic structures. Here, authors manipulate the electron spin polarization of TiO2 by tuning the concentration of Ti vacancies and show improved photocatalytic activities. [ABSTRACT FROM AUTHOR]

High-energy-density (HED) fuels are widely used in aerospace engines bit suffer front slow trance and incomplete combustion. A proposed solution to this problem is dissolution of a flammable small-molecule additive, a g., acetylene, in the fuel. The solubility of acetylene in HED fuels JP-10 and QC at 298.15 K and pressure from 0 to 200 kPa was studied. The molar concentration of acetylene in JP-10 and QC fuels or a pressure of 100 kPa reached 0.60 and 0.75%, respectively. Studies of the dissolution of acetylene in the presence of Et3N and scrambled cages (1, 2, and 5 mass%) showed that such additives could increase significantly the solubility of acetylene in the fuel. The research results are of practical interest for improving the efficiency of HED fuels. [ABSTRACT FROM AUTHOR]

High energy density fuels are critical for hypersonic aerospace propulsion but suffer from difficulties of ignition delay and incomplete combustion. This research reports aluminum nanoparticles (Al NPs) assisted ignition and combustion of high energy density JP-10 fuel. Al NPs with a size of 16 nm were fabricated through a mild and simple method by decomposing AlH3·Et2O with the addition of a surfactant ligand. The uniform size distribution, nanoscaled size and surface ligand make Al NPs stably suspend in JP-10, with 80% NPs being dispersed in the liquid fuel after six months. A shock tube test shows that the presence of 1 wt-% Al NPs can significantly shorten ignition delay time at temperature of 1500 to 1750 K, promote the combustion, and enhance energy release of JP-10. This work demonstrates the potential of Al NPs as ignition and combustion additive for high energy density fuel in hypersonic applications. [ABSTRACT FROM AUTHOR]

Harvesting ambient mechanical energy is a key technology for realizing self-powered electronics. With advantages of stability and durability, a liquid-solid-based triboelectric nanogenerator (TENG) has recently drawn much attention. However, the impacts of liquid properties on the TENG performance and the related working principle are still unclear. We assembled herein a U-tube TENG based on the liquid-solid mode and applied 11 liquids to study the effects of liquid properties on the TENG output performance. The results confirmed that the key factors influencing the output are polarity, dielectric constant, and affinity to fluorinated ethylene propylene (FEP). Among the 11 liquids, the pure water-based U-tube TENG exhibited the best output with an open-circuit voltage (Voc) of 81.7 V and a short-circuit current (Isc) of 0.26 μA for the shaking mode (0.5 Hz), which can further increase to 93.0 V and 0.48 μA, respectively, for the horizontal shifting mode (1.25 Hz). The U-tube TENG can be utilized as a self-powered concentration sensor (component concentration or metalion concentration) for an aqueous solution with an accuracy higher than 92%. Finally, an upgraded sandwich-like water-FEP U-tube TENG was applied to harvest water-wave energy, showing a high output with Voc of 350 V, Isc of 1.75 μA, and power density of 2.04 W/m3. We successfully lighted up 60 LEDs and powered a temperature-humidity meter. Given its high output performance, the water-FEP U-tube TENG is a very promising approach for harvesting water-wave energy for self-powered electronics. [ABSTRACT FROM AUTHOR]

The electronic structures and magnetic properties of strained monolayer MnPSe3 are investigated systematically via first-principles calculations. It is found that the magnetic ground state of monolayer MnPSe3 can be significantly affected by biaxial strain engineering, while the semiconducting characteristics are well-preserved. Owing to the sensitivity of the magnetic coupling towards structural deformation, a biaxial tensile strain of approximately 13% can lead to an antiferromagnetic (AFM)- ferromagnetic (FM) transition. The strain-dependent magnetic stability is mainly attributed to the competition of the direct AFM interaction and indirect FM superexchange interaction between the two nearest-neighbor Mn atoms. In addition, we find that FM MnPSe3 is an intrinsic half semiconductor with large spin exchange splitting in the conduction bands, which is crucial for the spin-polarized carrier injection and detection. The sensitive interdependence among the external stimuli, electronic structure, and magnetic coupling makes monolayer MnPSe3 a promising candidate for spintronics. [ABSTRACT FROM AUTHOR]