Search Results (265)

Developing cost-effective, sustainable, and high-performance air electrode catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a significant challenge in the advancement of rechargeable zinc–air batteries (ZABs). Herein, we successfully construct a vacancy-rich heterogeneous perovskite La_0.85Y_0.15Ni_0.7Fe_0.3O₃ (LYNF) hybridized with Co₃O₄ spinel nanoparticles using a simple chemical bath-assisted method. The Co₃O₄ composite LYNF material is systematically evaluated as the bifunctional catalyst for ZABs in the proportion of 25 wt%, 50w t%, and 75 wt% (denoted as LYNF-xCo₃O₄, x = 0.25, 0.5, 0.75). The results confirm an intimate coupling between the perovskite and spinel phases, along with a significant increase in oxygen vacancy concentration. Among the composites, LYNF-0.5Co₃O₄ exhibits the best performance, achieving an ORR onset potential of 0.813 V vs. RHE at −0.1 mA cm⁻² and a lower OER overpotential of 441 mV at 10 mA cm⁻². When applied as the air electrode catalyst in ZABs, LYNF-0.5Co₃O₄ displays the highest discharge voltage and a peak power density of 115 mW cm⁻², representing a 20% improvement over pristine LYNF. The enhanced performance of the LYNF-0.5Co₃O₄ composite is attributed to the accumulation of Co₃O₄ nanoparticles within the LYNF matrix, which introduces numerous electrochemically active sites and facilitates the charge and mass transport during the catalytic process in ZABs. Full article

Electrochemical water splitting for hydrogen production is considered a key pathway for achieving sustainable energy conversion. However, the sluggish reaction kinetics of the oxygen evolution reaction (OER) and high overpotentials severely hinder the large-scale application of water electrolysis technology. Nickel–iron layered double hydroxide (NiFe-LDH) has gained attention as a promising non-precious metal OER catalyst due to its abundant active sites and good intrinsic activity. However, its relatively low conductivity and charge transfer efficiency limit the improvement of catalytic performance. Therefore, this study used a simple hydrothermal method to generate a NiFe-LDH/Cs_0.32WO₃ heterojunction composite catalyst, relying on the excellent electronic conductivity of Cs_0.32WO₃ to improve overall charge transfer efficiency. According to electrochemical testing results, the modified NiFe-LDH/Cs_0.32WO₃-20 mg achieved a low overpotential of 349 mV at a current density of 10 mA cm⁻², a Tafel slope of 67.0 mV dec⁻¹, and a charge transfer resistance of 65.1 Ω, which represent decreases of 39 mV, 23.1%, and 40%, respectively, compared to pure NiFe-LDH. The key to performance improvement lies in the tightly bonded heterojunction interface between Cs_0.32WO₃ and NiFe-LDH. X-ray photoelectron spectroscopy (XPS) shows a distinct interfacial charge transfer phenomenon, with a notable negative shift of the W4f peak (0.85 eV), indicating the directional transfer of electrons from Cs_0.32WO₃ to NiFe-LDH. Under the influence of the built-in electric field within the heterojunction, this interfacial charge redistribution improved the electronic structure of NiFe-LDH, increased the proportion of high-valent metal ions, and significantly enhanced the OER reaction kinetics. This study provides new insights for the preparation of efficient heterojunction electrocatalysts. Full article

Lithium/carbon fluoride (Li/CF_x) batteries are promising for specialized applications due to their high theoretical capacity (>865 mAh·g⁻¹) and energy density. However, their practical deployment is hindered by the intrinsically low conductivity of CF_x and sluggish reaction kinetics. While conventional conductive additives improve electron transport, their physical mixing with active materials yields weak interfacial contacts and fails to catalytically facilitate C–F bond cleavage. To address these dual limitations, this study proposes a dual-functional conductive-catalytic additive strategy. We engineered zinc-nickel/carbon nanotube (ZnNi/CNT) composites modified with transition metal dopants (Fe, W, Cu) to integrate conductive networks with nanoscale-dispersed catalytic sites. Fe-doped ZnNi/CNT (ZnFeNiC) emerged as the optimal system, delivering a discharge plateau of 2.45 V and a specific capacity of 810.3 mAh·g⁻¹ at 0.1 C. This performance is attributed to Fe-doping accelerates Li⁺ diffusion, and promotes reversible Ni redox transitions (Ni²⁺↔Ni⁰) that catalyze C–F bond dissociation. This work establishes a design paradigm for high-performance Li/CF_x batteries, bridging the gap between conductive enhancement and catalytic activation. Full article

Petrological knowledge on weathering processes controlling the mobility of chemical elements is still limited in the dry tropical zone of Cameroon. This study aims to investigate the mobility of major and trace elements during rhyolite weathering and soil formation in Mobono by understanding the mineralogical and elemental vertical variation. The studied soil was classified as Cambisols containing mainly quartz, K-feldspar, plagioclase, smectite, kaolinite, illite, calcite, lepidocrocite, goethite, sepiolite, and interstratified clay minerals. pH values ranging between 6.11 and 8.77 indicated that hydrolysis, superimposed on oxidation and carbonation, is the main process responsible for the formation of secondary minerals, leading to the formation of iron oxides and calcite. The bedrock was mainly constituted of SiO₂, Al₂O₃, Na₂O, Fe₂O₃, Ba, Zr, Sr, Y, Ga, and Rb. Ce and Eu anomalies, and chondrite-normalized La/Yb ratios were 0.98, 0.67, and 2.86, respectively. SiO₂, Al₂O₃, Fe₂O₃, Na₂O, and K₂O were major elements in soil horizons. Trace elements revealed high levels of Ba (385 to 1320 mg kg⁻¹), Zr (158 to 429 mg kg⁻¹), Zn (61 to 151 mg kg⁻¹), Sr (62 to 243 mg kg⁻¹), Y (55 to 81 mg kg⁻¹), Rb (1102 to 58 mg kg⁻¹), and Ga (17.70 to 35 mg kg⁻¹). LREEs were more abundant than HREEs, with LREE/HREE ratio ranging between 2.60 and 6.24. Ce and Eu anomalies ranged from 1.08 to 1.21 and 0.58 to 1.24 respectively. The rhyolite-normalized La/Yb ratios varied between 0.56 and 0.96. Mass balance revealed the depletion of Si, Ca, Na, Mn, Sr, Ta, W, U, La, Ce, Pr, Nd, Sm, Gd and Lu, and the accumulation of Al, Fe, K, Mg, P, Sc, V, Co, Ni, Cu, Zn, Ga, Ge, Rb, Y, Zr, Nb, Cs, Ba, Hf, Pb, Th, Eu, Tb, Dy, Ho, Er, Tm and Yb during weathering along the soil profile. Full article

The interface between high-performance thermoelectric materials and electrodes critically governs the conversion efficiency and long-term reliability of thermoelectric generators under high-temperature operation. Here, we propose Al_xCoCrFeNi high-entropy alloys (HEA) as barrier layers to bond Cu-W electrodes with p-type skutterudite (p-SKD) thermoelectric materials. The HEA/p-SKD interface exhibited excellent chemical bonding with a stable and controllable reaction layer, forming a dense, defect-free (Fe,Ni,Co,Cr)Sb phase (thickness of ~2.5 μm) at the skutterudites side. The interfacial resistivity achieved a low value of 0.26 μΩ·cm² and remained at 7.15 μΩ·cm² after aging at 773 K for 16 days. Moreover, the interface demonstrated remarkable mechanical stability, with an initial shear strength of 88 MPa. After long-term aging for 16 days at 773 K, the shear strength retained 74 MPa (only 16% degradation), ranking among the highest reported for thermoelectric materials/metal joints. Remarkably, the joint maintained a shear strength of 29 MPa even after 100 continuous thermal cycles (623–773 K), highlighting its outstanding thermo-mechanical stability. These results validate the Al_xCoCrFeNi high-entropy alloys as an ideal interfacial material for thermoelectric generators, enabling simultaneous optimization of electrical and mechanical performance in harsh environments. Full article

In this study, we present a comprehensive theoretical analysis of modifications in the physical and chemical properties of MoSe₂ upon the introduction of substitutional transition metal impurities, specifically, Ti, V, Cr, Fe, Co, Ni, Cu, W, Pd, and Pt. Wet systematically calculated the adsorption enthalpies for various representative analytes, including O₂, H₂, CO, CO₂, H₂O, NO₂, formaldehyde, and ethanol, and further evaluated their free energies across a range of temperatures. By employing the formula for probabilities, we accounted for the competition among molecules for active adsorption sites during simultaneous adsorption events. Our findings underscore the importance of integrating temperature effects and competitive adsorption dynamics to predict the performance of highly selective sensors accurately. Additionally, we investigated the influence of temperature and analyte concentration on sensor performance by analyzing the saturation of active sites for specific scenarios using Langmuir sorption theory. Building on our calculated adsorption energies, we screened the catalytic potential of doped MoSe₂ for CO₂-to-methanol conversion reactions. This paper also examines the correlations between the electronic structure of active sites and their associated sensing and catalytic capabilities, offering insights that can inform the design of advanced materials for sensors and catalytic applications. Full article

In this work, the W element, with a larger atomic radius compared to Co, Fe, and Ni, was added to modify the microstructure and enhance the yield strength of CoFeNi medium entropy alloy (MEA). A detailed study was conducted to clarify the effects of W additions and annealing temperatures on the microstructure evolution and mechanical properties of CoFeNiW_x (x = 0, 0.1, and 0.3) MEAs. CoFeNiW_0.1 retained a single FCC structure without the formation of precipitates in the FCC phase, indicating that W, with a larger atomic radius, can completely dissolve in CoFeNiW_0.1. For CoFeNiW_0.3 MEA, coarse particles with an average diameter of ~2 μm appeared after homogenizing. Nevertheless, when the alloy was annealed at 800 °C and 900 °C, fine particles formed, with the average diameters of approximately 144 nm and 225 nm, respectively. After annealing at 800 °C, the CoFeNiW_0.3 with a partially recrystallized microstructure exhibited better comprehensive mechanical properties. Full article

An analysis of the working surfaces of cylindrical gears after scuffing shock tests allowed for the assessment of the effect of loading conditions on the form of damage to the tooth surfaces. Unlike the method of scuffing under severe conditions, where loading is applied gradually, the presented tests employed direct maximum loading—shock loading—without prior lapping of the gears under lower loads. This loading method significantly increases the vulnerability of the analyzed components to scuffing, enabling an evaluation of their limit in terms of operational properties. To identify the changes and the types of the teeth’s working surface damage, the following microscopy techniques were applied: scanning electron microscopy (FE-SEM) with EDS microanalyzer, optical interferential profilometry (WLI), atomic force microscope (AFM), and optical microscopy. The results allowed us to define the characteristic damage mechanisms and assess the efficiency of the applied DLC coatings when it comes to resistance to scuffing in shock scuffing conditions. Tribological tests were performed by means of an FZG T-12U gear test rig in a power circulating system to test cylindrical gear scuffing. The gears were made from 18CrNiMo7-6 steel and 35CrMnSiA nano-bainitic steel and coated with W-DLC/CrN. Full article

We report the fabrication of CoFeP-Ni(OH)₂/nickel foam (NF) composite electrodes via a two-step strategy involving the hydrothermal synthesis of Ni(OH)₂ on nickel foam followed by the electrochemical deposition of CoFeP. The integration of the Ni(OH)₂ interlayer not only provides a structurally robust interface but also facilitates synergistic redox activity, thereby significantly boosting the pseudocapacitive behavior of the electrode. Comparative analysis with bare CoFeP/NF reveals that the presence of the Ni(OH)₂ layer contributes to enhanced charge transfer efficiency and an increased electroactive surface area. Among the samples prepared under varying deposition cycles, the optimized CoFeP-Ni(OH)₂/NF electrode exhibits a high areal capacitance of 4244 mF cm⁻² at 2 mA cm⁻². Furthermore, an asymmetric supercapacitor device assembled with CoFeP-Ni(OH)₂/NF as the positive electrode and activated carbon as the negative electrode delivers a maximum energy density of 0.19 mWh cm⁻² at a power density of 0.37 mW cm⁻² and excellent cycling stability, retaining 72% of its initial capacitance after 5000 cycles at a high current density of 8 mA cm⁻². Full article

Transition metal oxides (TMOs) are considered to be highly promising materials for supercapacitor electrodes due to their low cost, multiple convertible valence states, and excellent electrochemical properties. However, inherent limitations, including restricted specific surface area and low electrical conductivity, have largely restricted their application in supercapacitors. In this paper, core–shell heterostructures of nickel–iron layered double hydroxide (NiFe-LDH) nanosheets uniformly grown on CuCo₂O₄ nanoneedles were synthesized by hydrothermal and calcination methods. It is found that the novel core–shell structure of CuCo₂O₄@NiFe-LDH improves the electrical conductivity of the electrode materials and optimizes the charge transport path. Under the synergistic effect of the two components and the core–shell heterostructure, the CuCo₂O₄@NiFe-LDH electrode achieves an ultra-high specific capacity of 323.4 mAh g⁻¹ at 1 A g⁻¹. And the capacity retention after 10,000 cycles at 10 A g⁻¹ is 90.66%. In addition, the assembled CuCo₂O₄@NiFe-LDH//RGO asymmetric supercapacitor device achieved a considerable energy density (68.7 Wh kg⁻¹ at 856.3 W kg⁻¹). It also has 89.36% capacity retention after 10,000 cycles at 10 A g⁻¹. These properties indicate the great potential application of CuCo₂O₄@NiFe-LDH in the field of high-performance supercapacitors. Full article

Fabricating eutectic high-entropy alloys (EHEAs) via selective laser melting (SLM) presents significant potential for advanced structural applications. This study explores the microstructural evolution of Fe₃₂Cr₃₃Ni₂₉Al₃Ti₃ EHEAs fabricated by SLM under varying laser powers. Electron backscatter diffraction (EBSD) analysis revealed that samples fabricated at 200 W exhibited approximately 70% face-centered-cubic (FCC) and 30% body-centered-cubic (BCC) phases. In comparison, those processed at 160 W showed an increased FCC fraction of 85% with a corresponding reduction in BCC content. Grain size measurements indicated that BCC grains were consistently finer than their FCC counterparts. Thermal simulations demonstrated that higher laser power produced deeper melt pools and broader temperature gradients. By correlating thermal history with phase diagram data, the spatial variation in BCC content was attributed to the differential residence time in the 1350–1100 °C range. This study represents one of the first attempts to quantitatively link local thermal histories with the evolution of dual-phase (FCC + BCC) microstructures in EHEAs during SLM. The findings contribute to the improved understanding and control of phase formation in complex alloy systems, providing valuable guidance for tailoring SLM parameters to optimize the phase composition and microstructure of EHEAs. Full article

This work studies the fabrication of CoCrFeNiMo high-entropy alloy (HEA) coatings via coaxial powder-fed laser cladding, addressing porosity and impurity issues in conventional methods. The HEA coatings exhibited eutectic/hypereutectic microstructures under all laser power conditions. A systematic investigation of laser power effects (1750–2500 W) reveals that 2250 W optimizes microstructure and performance, yielding a dual-phase structure with FCC matrix and dispersed σ phases (Fe-Cr/Mo-rich). The coating achieves exceptional hardness (738.3 HV_0.2, 3.8× substrate), ultralow wear rate (4.55 × 10⁻⁵ mm³/N·m), and minimized corrosion current (2.31 × 10⁻⁴ A/cm²) in 3.5 wt.% NaCl. The friction mechanism of the CoCrFeNiMo HEA coating is that in high-speed friction and wear, the oxide film is formed on the surface of the coating, and then the rupture of the oxide film leads to adhesive wear and abrasive wear. The corrosion mechanism is the galvanic corrosion caused by the potential difference between the FCC phase and the σ phase. Full article

Ti-2Al-9.2Mo-2Fe (2A2F) alloy is a low-cost β-Ti alloy in which the expensive β-stabilizing elements (Ta, Nb, W, Ni) are replaced with relatively inexpensive Mo and Fe for use in low-cost applications in various industries. The 2A2F alloy exhibits excellent mechanical properties such as high specific strength and low elastic modulus compared to conventional steel alloys but is prone to brittleness owing to the formation of the ω phase when heat-treated at relatively low temperatures. Therefore, an appropriate aging treatment should be performed to control the precipitation of the isothermal ω phase and secondary α phase. This study aims to derive the appropriate aging-treatment conditions following a solution treatment at 790 °C for 1 h, which is below the β-transus temperature of 815 °C. The aging treatments are conducted at holding temperatures in the range of 450–600 °C and holding times between 1 and 18 h. At relatively low aging temperatures of 450 °C and 500 °C, the precipitation of the isothermal ω phase resulted in significantly high hardness and compressive strength. As the aging temperature and holding time increased, the ω phase gradually transformed into the secondary α phase, leading to a balanced combination of strength and ductility. However, at excessively high aging temperatures and prolonged durations, excessive precipitation and growth of secondary α phases occurred, which caused a reduction in hardness and compressive strength, accompanied by an increase in ductility. In this study, the effects of precipitation evolution on mechanical properties such as tensile strength and hardness under various heat treatment conditions were comparatively analyzed. Full article

Multi-principal element alloys (MPEAs) exhibit distinct characteristics compared to conventional single-principal element-based metallic materials, primarily due to their unique design, resulting in intricate microstructural features. Currently, a comprehensive understanding of the fabrication processes, compositional design, and microstructural influence on the tribological and corrosion behavior of multi-component alloys remains limited. While the hardness of MPEAs generally correlates positively with wear resistance, with higher hardness typically associated with improved wear resistance and reduced wear rates, quantitative relationships between these properties are not well established. In this study, the Al₁₀Cr₁₇Fe₂₀NiV₄ alloy was selected as a model system. A homogeneous Al₁₀Cr₁₇Fe₂₀NiV₄ alloy was successfully synthesized via mechanical alloying followed by spark plasma sintering (SPS). To further investigate the correlation between hardness and wear rate, varying concentrations of alumina nanoparticles were incorporated into the alloy matrix as a reinforcing phase. The results revealed that the Al₁₀Cr₁₇Fe₂₀NiV₄ alloy exhibited a single-phase face-centered cubic (FCC) structure, which was maintained with the addition of alumina nanoparticles. The hardness of the Al₁₀Cr₁₇Fe₂₀NiV₄ alloy without nano-alumina was 727 HV, with a corresponding wear rate of 2.9 × 10⁻⁴ mm³·N⁻¹·m⁻¹. The incorporation of nano-alumina increased the hardness to 823 HV, and significantly reduced the wear rate to 1.6 × 10⁻⁴ mm³·N⁻¹·m⁻¹, representing a 45% reduction. The Al₂O₃ nanoparticles effectively mitigated alloy wear through crack passivation and matrix strengthening; however, excessive addition reversed this effect due to the agglomeration-induced brittleness and thermal mismatch. The quantitative relationship between hardness (HV) and wear rate (W) was determined as W = 2348 e^(−0.006HV). Such carefully bounded empirical relationships, as demonstrated in studies of cold-formed materials and dental enamel, remain valuable tools in applied research when accompanied by explicit scope limitations. Full article

Polycrystalline nickel–zinc (NiZn) ferrites are widely used in high-frequency applications due to their excellent magnetic properties such as low power losses, high magnetic permeability, and adequate saturation induction. However, data on their power loss behavior at 10 MHz, particularly at elevated temperatures, remain limited in the literature. This study investigates the magnetic performance of Co-doped NiZn ferrites at 10 MHz, under varying induction fields (3–10 mT) and temperatures (20–120 °C), with a focus on reducing high-temperature losses. Ferrite samples were synthesized using the conventional mixed oxide method and systematically varied in composition (Fe, Co content and Ni/Zn molar ratio). Key findings reveal that the incorporation of cobalt significantly enhances high-temperature performance by shifting resonance frequencies, attributed to increased domain wall pinning. Samples with optimized compositions and processing demonstrated power losses at 10 MHz, 10 mT and 25 °C, 100 °C and 120 °C as low as 310 mW cm⁻³, 1233 mW cm⁻³ and 1400 mW cm⁻³, respectively, with relative initial permeabilities exceeding 80 at these temperatures. These results provide insights into the design of high-frequency magnetic components and highlight strategies to minimize high-temperature losses. Full article