Elevated Operating Temperatures Research Articles

Method and application of surface modification of Cerium dioxide

Airborne pollutants, such as nitrogen oxides (NOx), and waterborne contaminants, including heavy metals, dyes, and other pollutants, pose substantial environmental threats and jeopardize human health. Additionally, certain limitations have hindered the widespread application of some batteries, primarily attributed to elevated operating temperatures and the decreasing use of fossil fuels. In response to these challenges, cerium dioxide (CeO2) nanoparticles have garnered considerable attention due to their unique and advantageous physical and chemical properties. Furthermore, the incorporation of CeO2 into various coating materials has demonstrated the potential to significantly enhance their performance. In the realm of biotechnology, research into CeO2 nanoparticles continues to expand, encompassing a range of applications such as the scavenging of reactive oxygen species (ROS) in biological systems, the development of anti‐inflammatory agents, and cancer research. Nevertheless, in these diverse applications, CeO2 still exhibits certain limitations that hinder the achievement of desired outcomes. The modification of CeO2 nanoparticles presents a promising avenue to address these limitations, thereby improving their overall efficacy. As such, this review aims to comprehensively compare and summarize various methods for the modification of CeO2 nanoparticles, elucidate their practical applications, and provide insights into the potential challenges and future prospects in this field.This article is protected by copyright. All rights reserved.

All-dielectric grating-assisted absorption enhancement in a subwavelength mercury cadmium telluride layer for infrared photodetectors

Light absorption enhancement in a 1.5 μm thick mercury–cadmium–telluride (Hg0.762Cd0.238Te, MCT) layer at room temperature utilizing 1D dielectric grating at mid-wave infrared (MWIR) wavelengths (3–5 μm) has been theoretically investigated. The optimized dielectric grating facilitates light diffraction and scattering into the MCT-absorbing waveguiding layer resulting in an increased lateral optical path. The light absorption was improved from ∼37.5% to ∼71% (TE) and ∼70% (TM) at normal incidence. With enhanced absorption, the photocarrier generation rate in the thin layer would be comparable to a bulk 5 μm thick MCT layer. A ∼3× reduction in the MCT layer thickness without compromising absorption has the potential for realizing infrared photodetectors with improved sensitivity at conventional operating temperatures and/or elevated operating temperatures.

Nb2O5 Microcolumns for Ethanol Sensing.

Pseudohexagonal Nb2O5 microcolumns spanning a size range of 50 to 610 nm were synthesized utilizing a cost-effective hydrothermal process (maintained at 180 °C for 30 min), followed by a subsequent calcination step at 500 °C for 3 h. Raman spectroscopy analysis unveiled three distinct reflection peaks at 220.04 cm-1, 602.01 cm-1, and 735.3 cm-1, indicative of the pseudohexagonal crystal lattice of Nb2O5. The HRTEM characterization confirmed the inter-lattice distance of 1.8 Å for the 110 plain and 3.17 Å for the 100 plain. The conductometry sensors were fabricated by drop-casting a dispersion of Nb2O5 microcolumns, in ethanol, on Pt electrodes. The fabricated sensors exhibited excellent selectivity in detecting C2H5OH (ΔG/G = 2.51 for 10 ppm C2H5OH) when compared to a variety of tested gases, including CO, CO2, NO2, H2, H2S, and C3H6O. The optimal operating temperature for this selective detection was determined to be 500 °C in a dry air environment. Moreover, the sensors demonstrated exceptional repeatability over the course of three testing cycles and displayed strong humidity resistance, even when exposed to 90% relative humidity. This excellent humidity resistance gas sensing property can be attributed to their nanoporous nature and elevated operating temperature.

Performance analysis of vanadium redox flow battery with interdigitated flow channel

As a key technology of energy storage system, vanadium redox flow battery has been used in the past few years. It is very important to explore the thermal behavior and performance of batteries. This study establishes a three-dimensional model of a vanadium redox flow battery with an interdigitated flow channel design. By adjusting the key parameters of the battery, the temperature and voltage changes of the battery are discussed. The electrochemistry, fluid mechanics, and multi physics phenomenon are involved in the model. Operating temperature, electrolyte flow rate, and current density are investigated as the important parameters. The results show that the electrolyte charge, mass transport, and electrochemical activity change at elevated operating temperature, and the battery discharge voltage increases with increasing the operating temperature. During the charging and discharging processes, the internal temperature of the battery also increases with the increase of the operating temperature, and the temperature distribution of the positive and negative electrodes is uniform, showing that the operating temperature has a slightly less effect on the temperature difference between the positive and negative electrodes. When the electrolyte flow rate is increased, since increasing the flow rate helps to increase the Coulombic efficiency, the discharge voltage of the battery also increases. When the current density is increased, the battery discharge state time is shortened, causing the discharge time to end faster.

(Digital Presentation) Study of Structural and Ionic Conductivity Property in Gd3+ and Sm3+ Co-Doped Ceria for Low Temperature SOFC Electrolyte Application

In recent years, fuel cells have become one of the most efficient and clean energy conversion devices. Due to their use in stationary as well as mobile power applications, they have also gained a lot of attention in this field. From all other fuel cells, SOFC has several advantages such as absence of liquid component, vibration free working, fuel and many more. However, two most crucial aspects of SOFC are operating temperature and the choice of electrolyte materials. It is the most efficient fuel cell with a setback in its elevated operating temperature, as high as around 800℃ -1000℃. To achieve high ionic conductivity in a SOFC, it is very important to tailor the electrolyte properties, simultaneously reducing the operating temperature.Conventionally, Yttria Stabilized Zirconia (YSZ) has been the most studied electrolyte material with a limiting factor of its high operating temperature. Doped Ceria has been one of the most explored alternatives of YSZ, which not only reduces the operating temperature but also enhances the ionic efficiency due to its electro-catalytic property. The double valency property of CeO2 occurring due to oxygen non-stoichiometry (CeO2-δ), generates oxygen vacancies making it a potential electrolyte material. Rare Earth (RE) dopants like Gd3+ and Sm3+ have reported to have high ionic conductivity at low temperatures. In the present study, synthesis of Sm-Gd- co-doped CeO2 by wet chemical route to ensure homogenous distribution, with the stoichiometry Ce1-a Gda-y Smy O2-0.5δ where a=0.20 and 0≤y≤a. It was prepared by modified co-precipitation method wherein, no additional water has been utilized during the co-precipitation process in order to minimize the particle agglomeration. Phase pure particles were obtained by calcining the precipitants at 650℃ in air and the green body made from it were sintered in air at elevated temperature of 1450 °C to achieve high density pellet. XRD and Raman spectroscopy confirmed successful substitution of both dopants and presence of single-phase cubic structure of the nanoparticles. The surface morphology was studied using FESEM which showed highly dense structure with more than 97% density. The electrochemical impedance spectroscopy (EIS) of the sintered pellets in the temperature range of 400-700℃, showed much higher conductivity then singly doped Ceria . Figure 1

Review and Prospects of PEM Water Electrolysis at Elevated Temperature Operation

AbstractPolymer electrolyte membrane water electrolyzers (PEMWE) are currently restricted to an operating temperature range between 50 to 80 °C. This review shows that elevated temperature (ET) above 90 °C can be advantageous with respect to i) reduced cell voltages, ii) a reduction of catalyst loading or possibly the employment of less noble electrocatalysts, and iii) a greater potential for waste heat utilization when the electrolyzer is operated in exothermal mode (when the cell voltage is higher than the thermoneutral voltage). Together with presenting an overview of the materials and components utilized in elevated temperature PEMWE under liquid and steam operation, this article summarizes the experimental and modeling performances reported to date, highlights the challenges ahead, and suggests aspects, which will need to be considered to improve the performance at elevated temperature. Key points, which arise from this work are the extensive need of re‐assessing the material selection both for the cell components and also at a system level, the effects and optimization of working with steam operation, and in the long run, the need for techno‐economic analyses to ultimately assess whether efficiency gains will truly translate to a cost‐effective technology alternative.

High Temperature Solid Oxide Electrolysis – Technology and Modeling

AbstractIn the global quest to renounce from fossil fuels, a large demand for the renewable production of hydrogen via water electrolysis exists. In this context, the solid oxide electrolyzer (SOE) is an interesting technology due to its high efficiency resulting from elevated operating temperatures of up to 900 °C. Physical modeling plays a vital role in the development of SOEs, as it lowers experimental costs and provides insight where measurements reach limits. A main challenge for modeling SOEs is the multitude of physical effects, occurring and interacting on various spatial and temporal scales. This requires assumptions and simplifications, particularly when increasing scope and dimensions of a model. In this review, we discuss the different approaches currently available in literature.

Critical performance comparisons between the high temperature and the low temperature proton exchange membrane fuel cells

Currently, there are only some general concepts about the performance difference between an LT-PEMFC (low temperature proton exchange membrane fuel cell) and an HT-PEMFC (high temperature proton exchange membrane fuel cell), i.e., no literature has been found to conduct direct comparisons between them. In this research, for the first time, according to the same level (low level, medium level or high level) under the same operating condition type (operating temperature or cathode air utilization rate), the tested I-V performance, EIS (electrochemical impedance spectroscopy), LSV (linear sweep voltammetry), and calculated ECSA (electrochemical surface area) are compared between LT-PEMFC and HT-PEMFC. Some mechanisms are further disclosed, for instance, the higher Pt loading in the catalyst layer of an HT-PEMFC and its elevated operating temperature do not result in improved performance, compared to that of the LT-PEMFC. This is attributed to the lower apparent exchange current density in the case of HT-PEMFC.

Efficient and geometry-matching two-stage annular thermoelectric generator for tubular solid oxide fuel cell waste heat recovery

Tubular solid oxide fuel cell (TSOFC) converts a great part of chemical energy within fuel into high-grade waste heat, leading to a decrease in overall fuel efficiency. In this paper, a steady-state hybrid system model based on TSOFC and two-stage annular thermoelectric generator (TATEG) is proposed. Considering various kinds of irreversible effects, mathematical model for the hybrid system is explicitly formulated and verified to guarantee the accuracy. Energetic and exergetic performance indexes of the hybrid system and subsystems are obtained, and the corresponding performance characteristics are revealed. Calculation results display that the power density, energetic and exergetic efficiencies of TSOFC-TATEG hybrid system can be 15.29 %, 11.25 % and 11.25 % higher than that of stand-alone TSOFC, respectively. The power density, energetic efficiency and exergetic efficiency of TSOFC-TATEG hybrid system are all increased by 5.65 % compared to that of TSOFC-ATEG hybrid system. Furthermore, this study reveals that enhancing the performance of the hybrid system is attainable through regulating variables, such as elevated operating temperatures, optimal quantities of thermoelectric elements, appropriate ratios between thermoelectric element numbers, well-considered thermocouple thickness, suitable thermocouple radial width, and the judicious selection of parameters like annular shape or height ratio.

Stable Harsh-Temperature Lithium Metal Batteries Enabled by Tailoring Solvation Structure in Ether Electrolytes.

For lithium metal batteries (LMBs), the elevated operating temperature results in severe capacity fading and safety issues due to unstable electrode-electrolyte interphases and electrolyte solvation structures. Therefore, it is crucial to construct advanced electrolytes capable of tolerating harsh environments to ensure stable LMBs. Here, we proposed a stable localized high-concentration electrolyte (LHCE) by introducing the highly solvating power solvent diethylene glycol dimethyl ether (DGDME). Computational and experimental evidence discloses that the original DGDME-LHCE shows favorable features for high-temperature LMBs, including high Li+-binding stability, electro-oxidation resistance, thermal stability, and nonflammability. The tailored solvated sheath structure achieves the preferred decomposition of anions, inducing the stable (cathode and Li anode)/interphases simultaneously, which enables a homogeneous Li plating-stripping behavior on the anode side and a high-voltage tolerance on the cathode side. For the Li||Li cells coupled with DGDME-LHCE, they showcase outstanding reversibility (a long lifespan of exceeding 1900 h). We demonstrate exceptional cyclic stability (∼95.59%, 250 cycles), high Coulombic efficiency (>99.88%), and impressive high-voltage (4.5 V) and high-temperature (60 °C) performances in Li||NCM523 cells using DGDME-LHCE. Our advances shed light on an encouraging ether electrolyte tactic for the Li-metal batteries confronted with stringent high-temperature challenges.

Surface-Catalyzed Zinc Oxide Nanorods and Interconnected Tetrapods as Efficient Methane Gas Sensing Platforms

Nanostructured metal oxide semiconductors have proven to be promising for the gas sensing domain. However, there are challenges associated with the fabrication of high-performance, low-to-room-temperature operation sensors for methane and other gases, including hydrogen sulfide, carbon dioxide, and ammonia. The functional properties of these semiconducting oxides can be improved by altering the morphology, crystal size, shape, and topology. Zinc oxide (ZnO) is an attractive option for gas sensing, but the need for elevated operating temperatures has limited its practical use as a commercial gas sensor. In this work, we prepared ZnO nanorod (ZnO-NR) arrays and interconnected tetrapod ZnO (T-ZnO) network sensing platforms as chemiresistive methane sensors on silicon substrates with platinum interdigitated electrodes and systematically characterized their methane sensing response in addition to their structural and physical properties. We also conducted surface modification by photochemical-catalyzed palladium, Pd, and Pd-Ag alloy nanoparticles and compared the uniformly distributed Pd decoration versus arrayed dots. The sensing performance was assessed in terms of target gas response magnitude (RM) and response percentage (R) recorded by changes in electrical resistance upon exposure to varying methane concentration (100–10,000 ppm) under thermal (operating temperatures = 175, 200, 230 °C) and optical (UV A, 365 nm illumination) excitations alongside response/recovery times, and limit of detection quantification. Thin film sensing platforms based on T-ZnO exhibited the highest response at 200 °C (RM = 2.98; R = 66.4%) compared to ZnO-NR thin films at 230 °C (RM = 1.34; R = 25.5%), attributed to the interconnected network and effective bandgap and barrier height reduction of the T-ZnO. The Pd-Ag-catalyzed and Pd dot-catalyzed T-ZnO films had the fastest response and recovery rates at 200 °C and room temperature under UV excitation, due to the localized Pd nanoparticles dots resulting in nano Schottky barrier formation, as opposed to the films coated with uniformly distributed Pd nanoparticles. The experimental findings present morphological differences, identify various mechanistic aspects, and discern chemical pathways for methane sensing.

Contribution of Electrolyte Decomposition Products and the Effect of Temperature on the Dissolution of Transition Metals from Cathode Materials.

A fundamental understanding of aging processes in lithium-ion batteries (LIBs) is imperative in the development of future battery architectures for widespread electrification. Herein, dissolution of transition metals from cathode active materials of LIBs is among the most important degradation processes. Research has demonstrated that elevated operating temperatures accelerate battery degradation. However, the exact mechanism of transition-metal dissolution at elevated temperatures has still to be clarified. Current literature suggests that the reaction rate of dissolution increases with increasing temperature; moreover, the decomposition of electrolytes results in products that also accelerate dissolution processes. Most studies focus on ex situ analyses of thermally treated full cells. This approach is not appropriate to get detailed insights and to distinguish between different contributions. In this work, with the help of real-time dissolution analysis using an electroanalytical flow cell (EFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS), we present novel details of the temperature effects on in situ dissolution at the cathode electrolyte interface. With fresh electrolytes, we find increased Mn dissolution even at open-circuit conditions as well as with constant voltage polarization when the electrode sample is heated at constant temperatures between 50 and 80 °C. The release of transition metals also responds in a nuanced manner when applying temperature transients. Utilizing electrolytes preheated at 60 and 100 °C, we demonstrate that decomposition products in the bulk electrolyte have no influence on transition-metal (TM) dissolution when constantly flushing the cell with the thermally aged electrolyte samples. Only when keeping the cathode temperature at 60 °C, the dissolution increases by a factor of 2-3. Our findings highlight the interplay between the cathode and electrolyte and provide new insights into the dissolution mechanism of cathode materials.

Fully Printed, High-Temperature Micro-Supercapacitor Arrays Enabled by a Hexagonal Boron Nitride Ionogel Electrolyte.

The proliferation and miniaturization of portable electronics require energy-storage devices that are simultaneously compact, flexible, and amenable to scalable manufacturing. In this work, mechanically flexible micro-supercapacitor arrays are demonstrated via sequential high-speed screen printing of conductive graphene electrodes and a high-temperature hexagonal boron nitride (hBN) ionogel electrolyte. By combining the superlative dielectric properties of 2D hBN with the high ionic conductivity of ionic liquids, the resulting hBN ionogel electrolyte enables micro-supercapacitors with exceptional areal capacitances that approach 1 mF cm-2 . Unlike incumbent polymer-based electrolytes, the high-temperature stability of the hBN ionogel electrolyte implies that the printed micro-supercapacitors can be operated at unprecedentedly high temperatures up to 180 °C. These elevated operating temperatures result in increased power densities that make these printed micro-supercapacitors particularly promising for applications in harsh environments such as underground exploration, aviation, and electric vehicles. The combination of enhanced functionality in extreme conditions and high-speed production via scalable additive manufacturing significantly broadens the technological phase space for on-chip energy storage.

Development and long-term field test of electrodeionization for decentralized desalination facility

Conventional desalination methods, such as distillation and reverse osmosis, are primarily utilized in large-scale plants. However, these techniques face challenges when implemented in decentralized facilities, such as in remote or underdeveloped areas, due to their high cost and complex systems requiring elevated temperature and pressure operations. With the advantages of relatively low operating pressure and temperature, electrodeionization (EDI) can be an alternative to conventional desalination methods. This study explores the potential application of EDI for small-scale decentralized desalination facilities. This study examines the performance of EDI under various operating conditions, including spacer thickness, applied voltage, water recovery, and feed flow rate. Based on the Porous Plug model analysis, the majority of the electric current circulates through the solid phase, possibly due to the high conductivity of the ion-exchange resins. EDI with 4 mm spacer thickness can achieve >99% salt removal at 20 V applied voltage, 75% water recovery, and 2 mL/s circulation flow rate. In addition, a thinner spacer thickness can enhance the desalination rate while lowering the final solution temperature. Furthermore, two-stage EDI can effectively maintain the salt-removal rate, suppress reverse salt diffusion, and reduce the desalination time. The long-term performance test indicates that EDI exhibits excellent performance stability.

High Temperature Superconductor Detector Magnets for Future Particle Physics Experiments

Particle physics experiments make use of magnetic fields up to 4T to bend electrically charged particles such that their charge and momentum can be determined. The particle energy measurement requires a low amount of material, or ma-terial that is highly transparent to particles inside the calorimeter volume. The conflict between the small volume of space reserved for a magnet and having a field of several teslas inside the detector is often resolved by using superconducting magnets. Up to now, large particle physics detector magnets have been constructed with low temperature superconductors, but there are clear benefits from using high temperature superconductors in future particle physics detector designs, such as allowing for an elevated operating temperature and the reduced amount of superconductor needed. In addition to the HTS material itself, additional material is needed to support the Lorentz forces, and to temporarily carry the current in case of a quench since these magnets are always one-of-a-kind and they need to operate reliably and without damage in case of a failure scenario. The stabilizer has to be a low-density material for high particle transparency, such as aluminium. Since the density of the superconductor is a factor of 4 higher than the density of aluminium, a reduction of superconducting material also means an improvement of the particle transparency: the density of a material is directly related to its particle transparency. This paper presents a conceptual design for high temperature superconducting detector magnets and a study of the type of aluminium stabilizer used.

Improving Photovoltaic Performance of Hybrid Organic-Inorganic MAGeI3 Perovskite Solar Cells via Numerical Optimization of Carrier Transport Materials (HTLs/ETLs).

In this study, a hybrid organic-inorganic perovskite solar cell (PSC) based on methylammonium germanium triiodide (MAGeI3), which is composed of methylammonium (CH3NH3+) cations and germanium triiodide (GeI3-) anions, has been numerically studied using SCAPS-1d codes. An extensive investigation of various electron transport layers (ETLs) and hole transport layers (HTLs) was conducted to identify the most optimal device configuration. The FTO/ZnOS/MAGeI3/PEDOT-WO3 structure performed the highest efficiency of all combinations tested, with an impressive optimized efficiency of 15.84%. This configuration exhibited a Voc of 1.38 V, Jsc of 13.79 mA/cm2, and FF of 82.58%. J-V characteristics and external quantum efficiency (EQE) measurements indicate that this device offers superior performance, as it has reduced current leakage, improved electron and hole extraction characteristics, and reduced trap-assisted interfacial recombination. Optimum device performance was achieved at active layer thickness of 560 nm. These findings may also serve as a basis for developing lightweight and ultra-thin solar cells, in addition to improving overall efficiency. Furthermore, a comprehensive correlation study was conducted to evaluate the optimum thickness and doping level for both ZnOS-ETL and PEDOT-WO3-HTL. The photovoltaic performance parameters of the FTO/ZnOS/MAGeI3/PEDOT-WO3 structure were analyzed over a wide temperature range (275 K to 450 K). The structure exhibited stable performance at elevated operating temperatures up to 385 K, with only minimal degradation in PCE of approximately 0.42%. Our study underscores the promise of utilizing cost-effective and long-term stability materials like ZnOS and PEDOT-WO3 alongside the toxic-free MAGeI3 perovskite. This combination exhibits significant potential for eco-friendly PSC, paving the way for the development of highly efficient ultra-thin PSC.

Revolutionizing n‐type Co3O4 Nanowire for Hydrogen Gas Sensing

This study presents conductometric sensors based on Co3O4 nanowires for hydrogen detection at ppb levels. The nanowires are synthesized through thermal oxidation of a 50 nm cobalt layer, exhibiting diameters between 6–50 nm and lengths of 1–5 μm, primarily growing along the (311) direction of spinal Co3O4. Raman investigation reveals five characteristic peaks at 195, 482, 521, 620, and 692 cm−1, corresponding to symmetric phonon modes of crystalline Co3O4. Electron paramagnetic resonance measurements confirm the presence of a ferromagnetic phase, attributed to incomplete cobalt oxidation, which disappears after 8 h of thermal aging at 400 °C. Conductometry measurements are performed in the temperature range of 300–500 °C. At temperatures above 300 °C, sensors exhibit abnormal n‐type semiconducting behavior due to lattice oxygen's involvement in the hydrogen sensing mechanism. Operating at 450 °C in dry air, the sensor shows a higher 232% response to 100 ppm H2 compared to ethanol, acetone, methane, carbon monoxide, and nitrogen dioxide. Remarkably, the sensor maintains a consistent conductance baseline even under high humidity (90%) for 25 d, with three‐cycle repeatability. This distinctive gas‐sensing capability is attributed to the catalytic activity and elevated operating temperature.

Thermophysical properties of additively manufactured (AM) GRCop-42 and GRCop-84

Additive manufacturing (AM) has enabled new opportunities of high-performance alloys for use in complex components across the aerospace, industrial, automotive, and energy industries. These industries have growing interest in copper alloys and AM for high-performance heat exchangers such as rocket engine combustion chambers. GRCop copper alloys, such as GRCop-84 (Cu-8Cr-4 Nb at%) and GRCop-42 (Cu-4Cr-2 Nb at%), have high thermal conductivity and high mechanical properties at elevated operating temperatures. In this paper, thermophysical properties for GRCop-84 and GRCop-42 produced using laser powder bed fusion (L-PBF) are examined. While L-PBF parameters and resulting microstructures can be achieved in a laboratory environment, those parameters do not always translate well into a production environment, and the variations across multiple machines and powder chemistries must be understood. The repeatability and reproducibility of samples across the commercial supply chain is critical for designers to ensure parts meet operational requirements. Thermophysical properties, such as thermal conductivity and thermal expansion are key design attributes. Thermal conductivities for eight GRCop-42 blocks and two GRCop-84 blocks were measured from room temperature up to 700 ℃. Thermal expansion was also measured from 20 °C to 1000 °C. These GRCop alloy parts were made with gas atomized powders from different vendors and with different L-PBF systems and parameters. Equations for the thermal conductivity and expansion are given. The variation of thermal conductivities for L-PBF GRCop parts is estimated to be less than + /− 4%. Based on phase analysis, compositional analysis, and thermal conductivity measurements, the small variations in thermal conductivities for the L-PBF GRCop parts are elucidated. The thermophysical property variations can be used to establish process capabilities and design guidelines for ongoing commercial use and further research.

A stable and highly-sensitive flexible gas sensor based on Ceria (CeO2) nano-cube decorated rGO nanosheets for selective detection of NO2 at room temperature

Sensing and monitoring nitrogen dioxide (NO2) gas is essential, due to its adverse effect on humans and the environment. However, conventional NO2 gas-sensing materials have limitations like elevated temperature operations, lower response, and low selectivity. Herewith, ceria nano-cube decorated reduced graphene oxide nanosheets (CeO2@rGO) were synthesized by a hydrothermal process, and as-synthesized products were characterized by various methods, viz. XRD, FE-SEM, FTIR, Raman spectrometer, BET, and IV characteristics. Afterwards, CeO2@rGO flexible gas sensor was fabricated by drop-cast technique, which is utilized for real-time monitoring of NO2 at room temperature (RT) (24ºC). Notably, the CeO2@rGO-based sensor upholds a significantly high response of 52.84 % towards 70 ppm of NO2, with an ultrafast response and recovery time of 7 s and 58 s respectively, with the LOD of 1 ppm. In addition, the CeO2@rGO flexible gas sensor exhibited long-term stability up to 30 days, solid repeatability, and stability in high relative humidity (RH) conditions. The marvelous sensing characteristics of the CeO2@rGO were attributed to the synergetic effect between CeO2 and rGO. The mechanism of sensing response was exhaustively interpreted by the “surface electron depletion layer mechanism”. Certainly, the scientific investigation conducted in the present study will undeniably advance the possible uses of detecting NO2 at RT.

Grain size and coercivity tuning in Nd2Fe14B-based magnets prepared by high pressure hydrogen milling

Nd2Fe14B-based permanent magnets play important role in the emerging green energy technologies due to their superb energy product (BH)max. High coercivity at elevated operating temperatures is crucial for device performance and as an extrinsic property it is largely determined by the microstructure of the magnet. In this work, we use high pressure hydrogen milling to reduce the average grain size in Nd2Fe14B powders towards the critical single domain regime to study the influence on the resultant coercivity. In addition, Nd content has been varied in a broad range to investigate how it affects the coercivity. Milling in 100 bar hydrogen enables complete decomposition of the Nd2Fe14B phase into α-Fe, NdH2 and Fe2B at nominally room temperature. A subsequent hydrogen desorption heat treatment leads to the recombination to the parent phase, now with nearly two orders of magnitude reduction in the grain size. The results show that indeed Hc peaks around the critical single domain grain size of ≈200 nm of Nd2Fe14B. Higher contents of Nd-rich grain boundary phase lead to a continuous increase in coercivity up to μ0Hc = 1.5 T, likely due to the suppression of long-range magnetostatic interactions between the nanocrystalline Nd2Fe14B grains.