Theoretical Investigation Research Articles

Theoretical and run-test investigation on a 50 MW beam-down concentrating solar power plant in China

The beam-down concentrating solar power plant has the advantages of high concentrating ratio, low installation and maintenance requirements, and low pump consumption. To conduct further theoretical and run-test evaluations of the optical and thermal performance of the beam-down concentrating solar power system, the Yumen Xinneng 50 MW beam-down power plant is analyzed in this research. The variation of the heliostat field efficiency, hyperboloid mirror flux density, receiver flux density, and annual power generation under various operating parameters is discussed. The run-test results from June 12th indicated an average outlet temperature of molten salt reached 559°C between 13:07 and 13:56 under an average direct normal irradiation of 739.7 W/m2. The corresponding inlet temperature increased from 302.3°C to 307.6°C due to the rewarming effect caused by the increase in hot molten salt. Regarding the simulation results, the recommended design parameters for the vertex ratio of the hyperboloid mirror are between 0.775 and 0.8 to mitigate the contradiction between initial investment and optical efficiency. The maximum values of cosine efficiency, shading and blocking efficiency, shading efficiency of the hyperboloid mirror, and attenuation efficiency for the heliostat field are 85.56%, 99.96%, 99.35%, and 97.46% on June 1st for the maximum solar elevation angle of 70.72°. Consequently, the maximum values of the average hyperboloid mirror flux density and receiver flux density are 11.2 kW/m2 and 399.1 kW/m2 on June 1st. The maximum power generation for a 7-day period is 4674.22 MWe in June with a duration time of 100 hours. This paper can further expand research on the comprehensive performance of beam-down power plants.

Theoretical Identification on Typical Fe3X (X=B, C, N) Compounds for Polysulfide Conversion in Lithium‐Sulfur Batteries

AbstractLi−S batteries (LSBs) are considered as the attractive candidates for next‐generation high‐energy system due to their high energy and low cost. However, their practical application is hindered by several stubborn issues, including the poor electric conductivity of sulfur cathodes, the shuttle of lithium polysulfides (LiPSs) and the slow dynamics during charge/discharge cycles. Transitional iron (Fe)‐based compounds are regarded as effectively electrocatalysts for polysulfide conversion by accelerating the reaction kinetics and enhancing the electric conductivity and electron/charge transfer. In this study, we investigate the typical transition Fe‐based compounds (Fe3X, X=B, C, N), known for their high catalytic ability, analyze their roles as sulfur host for LSBs using density functional theory (DFT). Our finding reveals that Fe3C and Fe3B surfaces exhibit more Fe‐S bonds compared to Fe3N surface, which explains the different electrochemical behaviors observed during battery testing with sulfur cathodes. Additionally, Fe3N demonstrates greater structural stability and effective polysulfide adsorption according to DFT calculations, outperforming the other two compounds in these aspects. We believe that this theoretical investigation would guide the identification of highly efficient hosts for sulfur cathodes and open new avenues for sulfur host selection in LSBs.

Interdisciplinary Investigations at the Intersection of Philosophy and Translation Studies

This article provides an overview of the challenges faced at the intersection of philosophy and translation studies. The interdisciplinary scope under consideration covers philosophical contributions to theoretical investigation of translation, which are substantively grounded in the experiences of practicing translators, amongst whom are philosophers. Furthermore, the paper emphasizes the prominent role of philosophy in establishing the fundamental conditions and concepts of translation, and addresses the numerous philosophical approaches contributing to the interdisciplinary discourse on the nature of translation. Considerable attention is given to metaphysical and epistemological points that seem to play a significant role in conceptualising translation issues and establishing the theoretical foundations of translation studies, as well as in providing a deeper insight into the translation process. On the whole, the philosophisation of the translation phenomenon contributes to the substantial growth of both philosophical thought and translation studies.

New Insight into the Electronic and Magnetic Properties of Sub-Stoichiometric WO3: A Theoretical Perspective

We present a theoretical investigation on the wide-band-gap semiconductor WO 3 in its room-temperature monoclinic structure. We carried out density functional theory and GGA-1/2 calculations on the bulk phase and the most stable (001) surface of the material, either in their stoichiometric form or in the presence of oxygen vacancies at various concentrations. Concerning the bulk phase, our results show how the inclusion of these defects correctly reproduces the intrinsic n-type doping of the material. The system is also found to be magnetic at reasonably high defect concentrations. As for the surface, the presence of vacancies gives rise to a magnetic behavior, whose features depend on the relative arrangement of native point defects. Oxygen vacancies are also responsible for additional tungsten oxidation states in both bulk and surface. Based on these results, we provide a rationale for the interpretation of most experimental data of this material and, possibly, other widespread transition metal oxides with similar properties and applications such as ReO 3, TiO 2, and SnO 2.

ВИЗНАЧЕННЯ ТЕХНОЛОГІЧНИХ ПАРАМЕТРІВ ЛАЗЕРНОГО ВИПРОМІНЕННЯ ДЛЯ ОТРИМАННЯ СУБМІКРО- ТА НАНОСТРУКТУР У ЗМІЦНЮВАЛЬНИХ ПОКРИТТЯХ НА СТАЛЯХ

Using the previously developed model of theoretical processes in the zone of laser irradiation, where thermal and thermomechanical processes are described, including the influence of crystallization energy and other internal energies during the formation of nanostructures at various temperature levels, further investigation of the thermal and thermomechanical characteristics of different structural steels during the formation of nanostructures on their surfaces using laser irradiation was conducted. To validate the model, temperature fields were determined in the zone of laser irradiation on steel 20 (Fig. 1a) and steel 50 (Fig. 1b), considering both heating and cooling processes. Calculations were performed for heat flux densities and durations of exposure close to those necessary for obtaining nanostructures (500...2000 K) and with temperature rise rates exceeding 10^7 K/s. As a result of calculations using the refined thermal model, temperature distributions at a depth of 1 μm during laser irradiation on steel with different carbon contents (steel 20, 38Х, 50, and У8) at various peak heat flux densities in the surface layer were obtained. A spatiotemporal distribution of temperatures along the radius of the laser spot and over time during laser irradiation with a heat flux density of q=3∙10^8 W/m^2 at a spot radius of 0.1 mm was constructed. Zones of nanostructure formation were identified depending on the heat flux density over the duration of laser irradiation. Theoretical investigations using the updated thermal model confirmed the need to consider the temperature rise rate, as exceeding it increases the likelihood of thermomechanical failure. At the same time, due to insufficient temperature rise rates during laser nanostructure formation in the surface layers of carbon steels, more micro- and sub microstructures are formed.

Four Generations of Volcano Plots for the Oxygen Evolution Reaction: Beyond Proton-Coupled Electron Transfer Steps?

ConspectusDue to its importance for electrolyzers or metal-air batteries for energy conversion or storage, there is huge interest in the development of high-performance materials for the oxygen evolution reaction (OER). Theoretical investigations have aided the search for active material motifs through the construction of volcano plots for the kinetically sluggish OER, which involves the transfer of four proton-electron pairs to form a single oxygen molecule. The theory-driven volcano approach has gained unprecedented popularity in the catalysis and energy communities, largely due to its simplicity, as adsorption free energies can be used to approximate the electrocatalytic activity by heuristic descriptors.In the last two decades, the binding-energy-based volcano method has witnessed a renaissance with special concepts being developed to incorporate missing factors into the analysis. To this end, this Account summarizes and discusses the different generations of volcano plots for the example of the OER. While first-generation methods relied on the assessment of the thermodynamic information for the OER reaction intermediates by means of scaling relations, the second and third generations developed strategies to include overpotential and kinetic effects into the analysis of activity trends. Finally, the fourth generation of volcano approaches allowed the incorporation of various mechanistic pathways into the volcano methodology, thus paving the path toward data- and mechanistic-driven volcano plots in electrocatalysis.Although the concept of volcano plots has been significantly expanded in recent years, further research activities are discussed by challenging one of the main paradigms of the volcano concept. To date, the evaluation of activity trends relies on the assumption of proton-coupled electron transfer steps (CPET), even though there is experimental evidence of sequential proton-electron transfer (SPET) steps. While the computational assessment of SPET for solid-state electrodes is ambitious, it is strongly suggested to comprehend their importance in energy conversion and storage processes, including the OER. This can be achieved by knowledge transfer from homogeneous to heterogeneous electrocatalysis and by focusing on the material class of single-atom catalysts in which the active center is well defined. The derived concept of how to analyze the importance of SPET for mechanistic pathways in the OER over solid-state electrodes could further shape our understanding of the proton-electron transfer steps at electrified solid/liquid interfaces, which is crucial for further progress toward sustainable energy and climate neutrality.

Focusing of mid-infrared polaritons through patterned graphene on van der Waals crystals

Abstract Manipulating the propagation of mid-infrared (mid-IR) light is crucial for optical imaging, biosensing, photocatalysis, and guiding photonic circuits. Artificially engineered metamaterials were introduced to comprehensively control optical waves. However, fabrication challenges and optical losses have impeded the progress. Fortunately, two-dimensional van der Waals (vdW) materials are alternatives because of their inherent optical properties, such as hyperbolic behavior, high confinement, low loss, and atomic-scale thickness. In this research, we conducted theoretical and numerical investigations on the α-phase molybdenum trioxide, a biaxial vdW material, with patterned graphene to assess the potential of the tunable focusing of mid-IR light. Our proposed method directly alters the path of excited light to focus mid-IR light by negative refraction. Further, the patterned graphene in our design offers enhanced focusing characteristics, featuring a significantly reduced waist diameter with 1/92 of the free-space wavelength, an enhanced beam quality without pronounced field ripples, and a fivefold increase in field intensity. Moreover, our approach significantly preserves the waist diameter of the focused beam while facilitating directional steering. Thus, the focused beam can propagate in a canalized manner toward the desired direction. These advancements lay the foundation for promising applications in planar photonics.

Theoretical and experimental investigations of vanadium pentoxide–based electrocatalysts for the hydrogen evolution reaction in alkaline media

AbstractA key approach towards better realization of intermittent renewable energy resources, namely, solar and wind, is green electrochemical hydrogen production from water electrolysis. In recent years, there have been increasing efforts aimed at developing noble metal-free electrocatalysts that are earth-abundant and electroactive towards hydrogen evolution reaction (HER) in alkaline electrolytes, wherein an initial water dissociation step is followed by a two-electron transfer cathodic reaction. Although relatively earth-abundant, vanadium-based electrocatalysts have been sparsely reported due to subpar electroactivity and kinetics towards water electrolysis in general and alkaline electrolysis in specific. Herein, we investigate the fine-tuning of orthorhombic V2O5-based electrocatalysts as candidates for HER through a scalable two-step sol–gel calcination procedure. Briefly, surface-induced anionic oxygen deficiencies and cationic dopants are synergistically studied experimentally and theoretically. To that end, first-principle facet-dependent density function theory (DFT) calculations were conducted and revealed that the coupling of certain dopants on V2O5 and co-induction of oxygen vacancies can enhance the catalytic HER performance by the creation of new electronic states near the Fermi level (EF), enhancing conductivity, and modulating surface binding of adsorbed protons, respectively. This was reflected experimentally through kinetically non-ideal alkaline electrochemical HER using Zn0.4V1.6O5 whereby − 194 mV of overpotential was required to attain − 10 mA/cm2 of current density, as opposed to pristine V2O5 which required 32% higher overpotential requirement at the same conditions. The disclosed work can be extended to other intrinsically sluggish transition metal (TM)–based oxides via the presented systematic tuning of surface and bulk microenvironment modulation. Graphical Abstract

Theoretical and experimental investigation of vibration-assisted scratching silicon

Interaction between tip and workpiece plays a crucial role in determining the scratching depth in Vibration-assisted Tip Based Nanofabrication (VTBN), which is more complicated than that of conventional scratching (without vibration-assisted). To establish the relationship between the scratching depth and machining parameters, a cubecorner indenter is employed to conduct VTBN procedure. The indenter is simplified as a cone to calculate the contact model in both 1D groove and 2D surface machining processes. An instantaneous normal load model is established based on the developed tip-workpiece contact model. Due to the variation of instantaneous contact area, effective contact area is put forward for the first time to predict the normal load. Effects of vibration frequency and amplitude on the normal load and surface quality are analyzed based on the proposed model. Experimental results show that higher frequency and larger amplitude will reduce the effective contact area. Vibration can increase the scratching depth and width without enlarging the cutting force. Furthermore, the inconsistency caused by scratching directions in conventional scratching is also overcome during VTBN.

Theoretical investigation of electromagnetic-thermal coupling of double-layer cylindrical concrete under microwave irradiation

Many experiments have been performed to study the heating properties of concrete under microwave irradiation. Microwave provides the non-uniform heating process, which cannot be reflected clearly through the experimental investigations. In this paper, a theoretical method is presented to investigate the electromagnetic-thermal coupling process of double-layer cylindrical concrete under microwave heating. The wave transmission and reflection were considered. An analytic solution is presented to predict transient heating process within a 3-dimensional double-layer concrete model induced by microwave heating. The inner aggregate is a microwave high loss material and the outer mortar was microwave low loss medium. Poynting theorem was employed to calculate the electric field distribution and microwave energy loss within concrete. Transient heat transfer process with an internal microwave heat source was investigated based on the classical heat transfer theory by employing integral transform technique. The results indicate that microwave heating effect depend on the concrete size, dielectric properties as well as microwave energy input. The temperature gradient was formed at the mortar-aggregate interface, which varied with the microwave heating parameters inputs. The analytical study will provide significant insight to promote the understanding of electric and temperature field in the two-layer composite concrete materials under microwave heating.

Theoretical investigation on action mechanism and mollifying efficacy of propellant stabilizers.

This project performed quantum chemical computation, through kinetic and thermodynamic analyses to compare relative reactivity, reaction rate, and equilibrium composition from the possible pathways in connection with stabilizer-nitrodioxide reactions to determine the stability of the materials for practical application. Corresponding achievements have promoted the use of N-methyl-p-nitroaniline (MNA) and dinitrophenyl malonamide series (M3, M4, and M5) stabilizers as high priorities for selection. The Gaussian 09 program (G09) (Frisch et al 2009) and density functional theory (DFT) calculations with the B3LYP/6-31G(d,p) function were performed to obtain related geometric and thermodynamic energy data for the molecular systems in this study. The synchronous transit-guided quasi-Newton method (STQN) (Peng and Schlegel Isr J Chem 33:49, 1993) was applied through the QST3 procedure to identify single imaginary frequency-valued transition-state species. The related reaction rate constant (k) and pre-exponential factor (A) were obtained, based on transition state theory (Su 2008), using Eqs. 11 and 12.

Narrow-linewidth Fano microcavities with resonant subwavelength grating mirror

We report on the theoretical and experimental investigations of optical microcavities consisting in the plane-plane arrangement of a broadband high-reflectivity mirror and a suspended one-dimensional grating mirror possessing a high-quality factor Fano resonance. By varying the length of these cavities from the millimeter to the few-micron range, we observe at short lengths the reduction of the spectral linewidth predicted to occur for such a Fano cavity as compared to a conventional broadband mirror cavity with the same length and internal losses. Such narrow linewidth and small modevolume microcavities with high-mechanical quality ultrathin mirrors will be attractive for a wide range of applications within optomechanics and sensing.

Regulating the Topology of Covalent Organic Frameworks for Boosting Overall H2O2 Photogeneration

Photocatalytic oxygen reduction reactions and water oxidation reactions are extremely promising green approaches for massive H2O2 production. Nonetheless, constructing effective photocatalysts for H2O2 generation is critical and still challenging. Since the network topology has significant impacts on the electronic properties of two dimensional (2D) polymers, herein, for the first time, we regulated the H2O2 photosynthetic activity of 2D covalent organic frameworks (COFs) by topology. Through designing the linking sites of the monomers, we synthesized a pair of novel COFs with similar chemical components on the backbones but distinct topologies. Without sacrificial agents, TBD‐COF with cpt topology exhibited superior H2O2 photoproduction performance (6085 and 5448 μmol g‐1 h‐1 in O2 and air) than TBC‐COF with hcb topology through the O2‐O2•‐‐H2O2, O2‐O2•‐‐O21‐H2O2, and H2O‐H2O2 three paths. Further experimental and theoretical investigations confirmed that during the H2O2 photosynthetic process, the charge carrier separation efficiency, O2•‐ generation and conversion, and the energy barrier of the rate determination steps in the three channels, related to the formation of *OOH, *O21, and *OH, can be well tuned by the topology of COFs. The current study enlightens the fabrication of high‐performance photocatalysts for H2O2 production by topological structure modulation.

Regulating the Topology of Covalent Organic Frameworks for Boosting Overall H2O2 Photogeneration.

Photocatalytic oxygen reduction reactions and water oxidation reactions are extremely promising green approaches for massive H2O2 production. Nonetheless, constructing effective photocatalysts for H2O2 generation is critical and still challenging. Since the network topology has significant impacts on the electronic properties of two dimensional (2D) polymers, herein, for the first time, we regulated the H2O2 photosynthetic activity of 2D covalent organic frameworks (COFs) by topology. Through designing the linking sites of the monomers, we synthesized a pair of novel COFs with similar chemical components on the backbones but distinct topologies. Without sacrificial agents, TBD-COF with cpt topology exhibited superior H2O2 photoproduction performance (6085 and 5448 μmol g-1 h-1 in O2 and air) than TBC-COF with hcb topology through the O2-O2•--H2O2, O2-O2•--O21-H2O2, and H2O-H2O2 three paths. Further experimental and theoretical investigations confirmed that during the H2O2 photosynthetic process, the charge carrier separation efficiency, O2•- generation and conversion, and the energy barrier of the rate determination steps in the three channels, related to the formation of *OOH, *O21, and *OH, can be well tuned by the topology of COFs. The current study enlightens the fabrication of high-performance photocatalysts for H2O2 production by topological structure modulation.

Corrosion Inhibition Effect of Quinoxaline Derivative on Carbon Steel in Hydrochloric Acid: Experimental and Theoretical Investigations

Corrosion Inhibition Effect of Quinoxaline Derivative on Carbon Steel in Hydrochloric Acid: Experimental and Theoretical Investigations

Theoretical Calculation Assisted by Machine Learning Accelerate Optimal Electrocatalyst Finding for Hydrogen Evolution Reaction

AbstractElectrocatalytic hydrogen evolution reaction (HER) is a promising strategy to solve and mitigate the coming energy shortage and global environmental pollution. Searching for efficient electrocatalysts for HER remains challenging through traditional trial‐and‐error methods from numerous potential material candidates. Theoretical high throughput calculation assisted by machine learning is a possible method to screen excellent HER electrocatalysts effectively. This will pave the way for high‐efficiency and low‐price electrocatalyst findings. In this review, we comprehensively introduce the machine learning workflow and standard models for hydrogen reduction reactions. This mainly illustrates how machine learning is used in catalyst filtration and descriptor exploration. Subsequently, several applications, including surface electrocatalysts, two‐dimensional (2D) electrocatalysts, and single/dual atom electrocatalysts using machine learning in electrocatalytic HER, are highlighted and introduced. Finally, the corresponding challenge and perspective for machine learning in electrocatalytic hydrogen reduction reactions are concluded. We hope this critical review can provide a comprehensive understanding of machine learning for HER catalyst design and guide the future theoretical and experimental investigation of HER catalyst findings.

Thickness dependent tribological and magnetic behavior of two-dimensional cobalt telluride (CoTe2)

Abstract Two-dimensional (2D) layered transition-metal based tellurides (chalcogens) are known to harness their surface atoms’ characteristics to enhance topographical activities for energy conversion, storage, and magnetic applications. The gradual stacking of each sheet alters the surface atoms’ subtle features such as lattice expansion, leading to several phenomena and rendering tunable properties. Here, we have evaluated thickness- dependent mechanical properties (nanoscale mechanics, tribology, potential surface distributions, interfacial interaction) of 2D CoTe2sheets and magnetic behavior using surface probe techniques. The experimental observations are further supported and explained with theoretical investigations: density functional theory (DFT) and molecular dynamics (MD). The variation in properties observed in theoretical investigations unleashes the crucial role of crystal planes of the CoTe2. The presented results are beneficial in expanding the use of the 2D telluride family in flexible electronics, piezo sensors, tribo-generators, and next-generation memory devices.

One-pot synthesis of NiCe-LDH for efficient electrochemical water splitting: A comprehensive experimental and theoretical study

The electrochemical splitting of water is a cost-effective and convenient way to generate H2 gas, utilizing readily available and affordable electrocatalysts. In the present report, a bimetallic LDH consisting of Ni and Ce (NiCe-LDH) was prepared via a very simple solvothermal method for the first time. The results showed that the solvothermal method produced NiCe-LDH nanoflakes with excellent potential for water electrolysis. The investigations found that the NC-2:1/NF sample had low overpotential of 110 mV with Tafel slope of 54.6 mV dec−1 in HER, while the NC-3:2/NF sample had low overpotential of 212 mV with Tafel slopes of 67.5 mV dec−1 in OER. Moreover, NiCe-LDH with NC-2:1 as a cathode and NC-3:2 as an anode provided a low cell voltage of 1.50 V at 10 mA cm−2 for the overall water-splitting reaction. Furthermore, a detailed theoretical investigation using DFT calculations was carried out to clear the mechanism of water electrolysis.

Theoretical Investigation of Nonmetallic Single-Atom Catalysts for Polysulfide Immobilization and Kinetic Enhancement in Lithium–Sulfur Batteries

Theoretical Investigation of Nonmetallic Single-Atom Catalysts for Polysulfide Immobilization and Kinetic Enhancement in Lithium–Sulfur Batteries

Homogenic Boundary Effect Boosted Oxygen Evolution Reaction in α/β‐NiMoO4 for Rechargeable Aqueous Zn‐Air Battery

AbstractRechargeable Zn‐air batteries (ZAB) represent a promising avenue for sustainable energy storage, boasting high energy density, cost‐effectiveness, scalability, and environmental friendliness. However, the sluggish redox kinetics and limited cycle life of bifunctional oxygen evolution/reduction (OER/ORR) electrocatalysts impede the further practical development of ZABs. In this study, homogenic boundary effect within α/β‐NiMoO4 is introduced as a superior electrocatalyst for ZAB. Through in situ poikilothermic X‐ray diffraction, X‐ray absorption spectroscopy, and theoretical investigations, the active Ni atoms exhibit more effective electron transfer at α/β‐NiMoO4 due to the homogenic boundary effect is unveiled. Furthermore, the presence of oxygen vacancies and lattice distortions at these boundaries significantly reduces the thermodynamic barrier of OER to a mere 0.46 V. Consequently, α/β‐NiMoO4 demonstrates a remarkably low overpotential of 270 mV at 10 mA cm−2 for the bottlenecked OER, along with prolonged durability (150 h) and a high specific capacity (745 mAh g−1 at 5 mA cm−2) for ZAB. This study underscores the efficacy of homogenic boundary effects in enhancing electrocatalytic activities, offering great promise for the advancement of sustainable energy systems.