Search Results (79)

Currently, the trade-off between oxygen permeation flux and structural stability in conventional perovskite oxides restricts the practical application of oxygen permeable membranes. In this study, a high-entropy design was applied to the B-site of BSCF matrix materials, resulting in the successful synthesis of a high-entropy perovskite, Ba_0.5Sr_0.5Co_0.71Fe_0.2Ta_0.03Ni_0.03Zr_0.03O_3−δ. The crystal structure, microstructure, and elemental composition of the material were systematically characterized and analyzed. Theoretical analysis and experimental characterization confirm that the material exhibits a stable single-phase high-entropy perovskite oxide structure. Under He as the sweep gas, the membrane achieved an oxygen permeation flux of 1.28 mL·cm⁻²·min⁻¹ and operated stably for over 100 h (1 mm thick, 900 °C). In a 20% CO₂/He atmosphere, the flux remained above 0.92 mL·cm⁻²·min⁻¹ for over 100 h, demonstrating good CO₂ tolerance. Notably, when the sweep gas is returned to the pure He atmosphere, the oxygen permeation flux fully recovers to 1.28 mL·cm⁻²·min⁻¹, with no evidence of leakage. These findings indicate that the proposed B-site doping strategy can break the trade-off between oxygen permeability and structural stability in conventional perovskite membranes. This advancement supports the industrialization of oxygen permeable membranes and offers valuable theoretical guidance for the design of high-performance perovskite materials. Full article

In this study, a novel anode-supported solid oxide fuel cell (SOFC) comprising a Bi₂O₃-doped NiO-ScSZ anode and an ScSZ electrolyte was successfully fabricated via a low-temperature co-sintering process at 1300 °C. The incorporation of 3 wt% Bi₂O₃ effectively promoted the sintering of both the anode support and electrolyte layer, resulting in a dense, gas-tight electrolyte and a mechanically robust porous anode support. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed the formation of phase-pure, highly crystalline ScSZ with an optimized microstructure. Electrochemical performance measurements demonstrated that the fabricated cells achieved excellent power density, reaching a peak value of 0.861 W cm⁻² at 800 °C under humidified hydrogen fuel conditions. The cells maintained stable performance under dry methane operation, with a maximum power density of 0.624 W cm⁻² at 800 °C, indicating resistance to carbon deposition. Gas chromatographic analyses further revealed that the Bi₂O₃-doped NiO-ScSZ anode facilitated earlier and more stable electrochemical oxidation of methane-derived species compared with the conventional NiO-YSZ system, even under conditions of an elevated methane partial pressure. These findings demonstrate that Bi₂O₃ co-doping, combined with low-temperature co-sintering, provides an effective approach for fabricating high-performance intermediate-temperature SOFCs with enhanced structural integrity and electrochemical stability. The developed methodology presents a promising pathway toward achieving cost-effective and durable SOFC technologies. Full article

The challenging problem of chlorine “poisoning” SnO₂ for poorly recoverable detection of dichloromethane has been solved in this work. The materials synthesized by Ni or/and Mo doping SnO₂ were spread onto the micro-hotplates (<1 mm³) to fabricate the MEMS sensors with a low power consumption (<45 mW). The sensor based on Mo·Ni co-doped SnO₂ is evidenced to have the best sensing performance of significant response and recoverability to dichloromethane between 0.07 and 100 ppm at the optimized temperature of 310 °C, in comparison with other sensors in this work and the literature. It can be attributed to a synergetic effect of Mo·Ni co-doping into SnO₂ as being supported by characterization of geometrical and electronic structures. The sensing mechanism of dichloromethane on the material is investigated. In situ infrared spectroscopy (IR) peaks identify that the corresponding adsorbed species are too strong to desorb, although it has demonstrated a good recoverability of the material. A probable reason is the formation rates of the strongly adsorbed species are much slower than those of the weakly adsorbed species, which are difficult to form significant IR peaks but easy to desorb, thus enabling the material to recover. Theoretical analysis suggests that the response process is kinetically determined by molecular transport onto the surface due to the free convection from the concentration gradient during the redox reaction, and the output steady voltage thermodynamically follows the equation only formally identical to the Langmuir–Freundlich equation for physisorption but is newly derived from statistical mechanics. Full article

Detecting low nitrogen dioxide concentrations (NO₂) is crucial for environmental monitoring. In this paper, we report the synergistic effect of decorating nitrogen-doped reduced graphene oxide (N-rGO) with nickel oxide (NiO) nanoparticles for developing highly selective and sensitive chemiresistive NO₂ gas sensors. The N-rGO/NiO sensor was synthesized straightforwardly, ensuring uniform decoration of NiO nanoparticles on the N-rGO surface. Comprehensive characterization using SEM, TEM, XRD, and Raman spectroscopy confirmed the successful integration of NiO nanoparticles with N-rGO and revealed key structural and morphological features contributing to its enhanced sensing performance. As a result, the NiO/N-rGO nanohybrids demonstrate a significantly enhanced response five orders of magnitude higher than that of N-rGO toward low NO₂ concentrations (<1 ppm) at 100 °C. Moreover, the present device has an outstanding performance, high sensitivity, and low limit of detection (<1 ppb). The findings pave the way for integrating these sensors into advanced applications, including environmental monitoring and IoT-enabled air quality management systems. Full article

Developing more effective gold–support synergy is essential for enhancing the catalytic performance of supported gold nanoparticles (AuNPs) in the gas-phase oxidation of ethanol to acetaldehyde (AC) at lower temperatures. This study demonstrates a significantly improved Au–support synergy achieved by copper doping in LaMO₃ (M = Mn, Fe, Co, Ni) perovskites. Among the various Au/LaMCuO₃ catalysts, Au/LaMnCuO₃ exhibited exceptional catalytic activity, achieving an AC yield of up to 91% and the highest space-time yield of 764 g_AC g_Au⁻¹ h⁻¹ at 225 °C. Notably, this catalyst showed excellent hydrothermal stability, maintaining performance for at least 100 h without significant deactivation when fed with 50% aqueous ethanol. Comprehensive characterization reveals that Cu doping facilitates the formation of surface oxygen vacancies on the Au/LaMCuO₃ catalysts and enhances Au–support interactions. The LaMnCuO₃ perovskite stabilizes the crucial Cu⁺ species, resulting in a stable Au-Mn-Cu synergy within the Au/LaMnCuO₃ catalyst, which facilitates the activation of O₂ and ethanol at lower temperatures. The optimization of the reaction conditions further improves AC productivity. Kinetic studies indicate that the cleavages of both the O-H bond and the α-C-H bond of ethanol are the rate-controlling steps. Full article

The objective of this work was to develop a highly active hydrotreating catalyst for processing heavy gas oil to provide qualified feedstock for hydroisomerization or a hydrocracking unit. The NiMo/γ-Al₂O₃ catalysts doped with phosphate were prepared by introducing two kinds of additives, and the influencing factors for highly active hydrodenitrogenation (HDN) were revealed. TEM analysis results showed that the catalyst with a small MoS2 stack length tended to have high activity due to more active sites being exposed. Laser Raman spectroscopy demonstrated that the catalysts contained PMo₁₂O₄₀³⁻ metal active phases. For industrial heavy VGO feedstock, the nitrogen content can be reduced to 2 ppm with a hydrotreating process. The VI of the hydrotreated product can be improved from 132 to 145 after hydrotreatment, which is necessary to produce group III base oil as the most valuable base oil type. This work provides an insight into the high activity of hydrotreating catalysts for industrial lubricant hydroprocessing. Full article

The study began by pre-sintering Ga₂O₃ powder at 950 °C for 1 h, followed by the preparation of a mixture of Ga₂O₃ and 12 at% NiO powders to fabricate a source target material. An electron beam (e-beam) system was then used to deposit NiO-doped Ga₂O₃ thin films on Si substrates. X-ray diffraction (XRD) analyses revealed that the pre-sintered Ga₂O₃ at 950 °C exhibited β-phase characteristics, and the deposited NiO-doped Ga₂O₃ thin films exhibited an amorphous phase. After the deposition of the NiO-doped Ga₂O₃ thin films, they were divided into two portions. One portion underwent various analyses directly, while the other was annealed at 500 °C in air before being analyzed. Field-emission scanning electron microscopy (FESEM) was utilized to process the surface observation, and the cross-sectional observation was primarily used to measure the thickness of the NiO-doped Ga₂O₃ thin films. UV-Vis spectroscopy was used to calculate the bandgap by analyzing the transmission spectra, while the Agilent B1500A was employed to measure the I-V characteristics. Hall measurements were also performed to assess the mobility, carrier concentration, and resistivity of both NiO-doped Ga₂O₃ thin films. The first innovation is that the 500 °C-annealed NiO-doped Ga₂O₃ thin films exhibited a larger bandgap and better electrical conductivity. The manuscript provides an explanation for the observed increase in the bandgap. Another important innovation is that the 500 °C-annealed NiO-doped Ga₂O₃ thin films revealed a high-energy bandgap of 4.402 eV. The third innovation is that X-ray photoelectron spectroscopy (XPS) analyses of the Ga_2p3/2, Ga_2p1/2, Ga_3d, Ni_2p3/2, and O_1s peaks were conducted to further investigate the reasons behind the enhanced electrical conductivity of the 500 °C-annealed NiO-doped Ga₂O₃ thin films. Full article

Doping engineering has been applied in niobium-doped NiO (NiO:Nb) by adding nitrogen (N) in its structure. The rf-sputtered films were made from a Ni-Nb composite target on unheated substrates at 300 W rf power and 5 mTorr total pressure. The plasma contained 50% Ar and 50% O₂ for the fabrication of the single-doped NiO:Nb film (AΝ film), and N₂ gas for the incorporation of N in the Ni-O-Nb structure. The N₂ in plasma was introduced by keeping constant the flow rates of O₂ and N₂ gasses (O₂/N₂ = 1) and reducing the amount of Ar gas, namely 94% Ar, 3% O₂, and 3% N₂ (film AN1); 50% Ar, 25% O₂, and 25% N₂ (film AN2); and 6% Ar, 47% O₂, and 47% N₂ (film AN3). All films had the single phase of cubic NiO and both Nb and N in the Ni-O structure were revealed by XPS experiments. The roughness of the films was increased with the increase in N in plasma. Post-deposition thermal treatment improved the crystallinity and reduced the structural disorder of the films. The AN2 film was found to be the most transparent of all films, exhibiting the widest band gap, 3.72 eV, and the narrowest Urbach tail states’ width, 313 meV. The AN and the AN2 films were employed to form NiO/TiO₂ heterostructures. The NiO:Nb/TiO₂ and NiO:(Nb,N)/TiO₂ heterostructures exhibited a visible transmittance of around 42% and 75%, respectively, and both showed rectification properties. Upon illumination with UV light, the NiO:(Nb,N)/TiO₂ diode exhibited enhanced photovoltaic performance when compared to the NiO:Nb/TiO₂ solar cell: the short-circuit current densities were 0.2 mA/cm² versus 1.4 μA/cm² and the open-circuit voltages were 0.5 V versus 0.2 V. The output characteristics of the p-NiO:(Nb,N)/n-TiO₂ UV photovoltaics can be further improved by proper engineering of the individual layers and device processing procedures. Full article

The emission of toxic gases from industrial production has intensified issues related to atmospheric pollution and human health. Consequently, the effective real-time monitoring and removal of these harmful gases have emerged as significant challenges. In this work, the density functional theory (DFT) method was utilized to examine the adsorption behaviors and electronic properties of the Ni-decorated InSe (Ni-InSe) monolayer when interacting with twelve gases (CO, NO, NO₂, NH₃, SO₂, H₂S, H₂O, CO₂, CH₄, H₂, O₂, and N₂). A comparative assessment of adsorption strength and sensing properties was performed through analyses of the electronic structure, work function, and recovery time. The results show that Ni doping enhances the electrical conductivity of the InSe monolayer and improves the adsorption capabilities for six toxic gases (CO, NO, NO₂, NH₃, SO₂, and H₂S). Furthermore, the adsorption of these gases on the Ni-InSe surface is characterized as chemisorption, as indicated by the analysis of the adsorption energy, density of states, and charge density difference. Additionally, the adsorption of CO, NO, NO₂, and SO₂ results in significant alterations to the bandgap of Ni-InSe, with changes of 18.65%, 11.37%, 10.62%, and −31.77%, respectively, underscoring its exceptional sensitivity. Moreover, the Ni-InSe monolayer exhibits a moderate recovery time of 3.24 s at 298 K for the SO₂. Consequently, the Ni-InSe is regarded as a promising gas sensor for detecting SO₂ at room temperature. This research establishes a foundation for the development of an Ni-InSe-based gas sensor for detecting and mitigating harmful gas emissions. Full article

Acetone detection is of significant importance in various industries, from cosmetics to pharmaceuticals, bioengineering, and paints. Sensor manufacturing involves the use of different semiconductor materials as well as different metals for doping and functionalization, allowing them to achieve advanced or unique properties in different sensor applications. In the healthcare field, these sensors play a crucial role in the non-invasive diagnosis of various diseases, offering a potential way to monitor metabolic conditions by analyzing respiration. This article presents the synthesis method, using chemical solutions and rapid thermal annealing technology, to obtain Al-functionalized and Ni-doped copper oxide (Al/CuO:Ni) nanostructured thin films for biosensors. The nanocrystalline thin films are subjected to a thorough characterization, with examination of the morphological properties by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. The results reveal notable changes in the surface morphology and structure following different treatments, providing insight into the mechanism of function and selectivity of these nanostructures for gases and volatile compounds. The study highlights the high selectivity of developed Al/CuO:Ni nanostructures towards acetone vapors at different concentrations from 1 ppm to 1000 ppm. Gas sensitivity is evaluated over a range of operating temperatures, indicating optimum performance at 300 °C and 350 °C with the maximum sensor signal (S) response obtained being 45% and 50%, respectively, to 50 ppm gas concentration. This work shows the high potential of developed technology for obtaining Al/CuO:Ni nanostructured thin films as next-generation materials for improving the sensitivity and selectivity of acetone sensors for practical applications as breath detectors in biomedical diagnostics, in particular for diabetes monitoring. It also emphasizes the importance of these sensors in ensuring industrial safety by preventing adverse health and environmental effects of exposure to acetone. Full article

Doping engineering is crucial for both fundamental science and emerging applications. While transition metal (TM) dopants exhibit considerable advantages in the tuning of magnetism and conductivity in bulk Ga₂O₃, investigations on TM-doped two-dimensional (2D) Ga₂O₃ are scarce, both theoretically and experimentally. In this study, the detailed variations in impurity levels within 3d TM-doped 2D Ga₂O₃ systems have been explored via first-principles calculations using the generalized gradient approximation (GGA) +U method. Our results show that the Co impurity tends to incorporate on the tetrahedral GaII site, while the other dopants favor square pyramidal GaI sites in 2D Ga₂O₃. Moreover, Sc³⁺, Ti⁴⁺, V⁴⁺, Cr³⁺, Mn³⁺, Fe³⁺, Co³⁺, Ni³⁺, Cu²⁺, and Zn²⁺ are the energetically favorable charge states. Importantly, a transition from n-type to p-type conductivity occurs at the threshold Cu element as determined by the defect formation energies and partial density of states (PDOS), which can be ascribed to the shift from electron doping to hole doping with respect to the increase in the atomic number in the 3d TM group. Moreover, the spin configurations in the presence of the square pyramidal and tetrahedral coordinated crystal field effects are investigated in detail, and a transition from high-spin to low-spin arrangement is observed. As the atomic number of the 3d TM dopant increases, the percentage contribution of O ions to the total magnetic moment significantly increases due to the electronegativity effect. Additionally, the formed 3d bands for most TM dopants are located near the Fermi level, which can be of significant benefit to the transformation of the absorbing region from ultraviolet to visible/infrared light. Our results provide theoretical guidance for designing 2D Ga₂O₃ towards optoelectronic and spintronic applications. Full article

A series of M(x)CoCeMgAlO mixed oxides with different transition metals (M = Cu, Fe, Mn, and Ni) with an M content x = 3 at. %, and another series of Fe(x)CoCeMgAlO mixed oxides with Fe contents x ranging from 1 to 9 at. % with respect to cations, while keeping constant in both cases 40 at. % Co, 10 at. % Ce and Mg/Al atomic ratio of 3 were prepared via thermal decomposition at 750 °C in air of their corresponding layered double hydroxide (LDH) precursors obtained by coprecipitation. They were tested in a fixed bed reactor for complete methane oxidation with a gas feed of 1 vol.% methane in air to evaluate their catalytic performance. The physico-structural properties of the mixed oxide samples were investigated with several techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), elemental mappings, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction under hydrogen (H₂-TPR) and nitrogen adsorption–desorption at −196 °C. XRD analysis revealed in all the samples the presence of Co₃O₄ crystallites together with periclase-like and CeO₂ phases, with no separate M-based oxide phase. All the cations were distributed homogeneously, as suggested by EDX measurements and elemental mappings of the samples. The metal contents, determined by EDX and ICP-OES, were in accordance with the theoretical values set for the catalysts’ preparation. The redox properties studied by H₂-TPR, along with the surface composition determined by XPS, provided information to elucidate the catalytic combustion properties of the studied mixed oxide materials. The methane combustion tests showed that all the M-promoted CoCeMgAlO mixed oxides were more active than the M-free counterpart, the highest promoting effect being observed for Fe as the doping transition metal. The Fe(x)CoCeMgAlO mixed oxide sample, with x = 3 at. % Fe displayed the highest catalytic activity for methane combustion with a temperature corresponding to 50% methane conversion, T₅₀, of 489 °C, which is ca. 40 °C lower than that of the unpromoted catalyst. This was attributed to its superior redox properties and lowest activation energy among the studied catalysts, likely due to a Fe–Co–Ce synergistic interaction. In addition, long-term tests of Fe(3)CoCeMgAlO mixed oxide were performed, showing good stability over 60 h on-stream. On the other hand, the addition of water vapors in the feed led to textural and structural changes in the Fe(3)CoCeMgAlO system, affecting its catalytic performance in methane complete oxidation. At the same time, the catalyst showed relatively good recovery of its catalytic activity as soon as the water vapors were removed from the feed. Full article

The present work deals with the development of Co₃O₄-based catalysts for potential application in catalytic gas sensors for methane (CH₄) detection. Among the transition-metal oxide catalysts, Co₃O₄ exhibits the highest activity in catalytic combustion. Doping Co₃O₄ with another metal can further improve its catalytic performance. Despite their promising properties, Co₃O₄ materials have rarely been tested for use in catalytic gas sensors. In our study, the influence of catalyst morphology and Ni doping on the catalytic activity and thermal stability of Co₃O₄-based catalysts was analyzed by differential calorimetry by measuring the thermal response to 1% CH₄. The morphology of two Co₃O₄ catalysts and two Ni_xCo_3−xO₄ with a Ni:Co molar ratio of 1:2 and 1:5 was studied using scanning transmission electron microscopy and energy dispersive X-ray analysis. The catalysts were synthesized by (co)precipitation with KOH solution. The investigations showed that Ni doping can improve the catalytic activity of Co₃O₄ catalysts. The thermal response of Ni-doped catalysts was increased by more than 20% at 400 °C and 450 °C compared to one of the studied Co₃O₄ oxides. However, the thermal response of the other Co₃O₄ was even higher than that of Ni_xCo_3−xO₄ catalysts (8% at 400 °C). Furthermore, the modification of Co₃O₄ with Ni simultaneously brings stability problems at higher operating temperatures (≥400 °C) due to the observed inhomogeneous Ni distribution in the structure of Ni_xCo_3−xO₄. In particular, the Ni_xCo_3−xO₄ with high Ni content (Ni:Co ratio 1:2) showed apparent NiO separation and thus a strong decrease in thermal response of 8% after 24 h of heat treatment at 400 °C. The reaction of the Co₃O₄ catalysts remained quite stable. Therefore, controlling the structure and morphology of Co₃O₄ achieved more promising results, demonstrating its applicability as a catalyst for gas sensing. Full article

This study synthesizes Ni-doped perovskite-structured LaFeO₃ composite materials via a one-step hydrothermal method, characterizes the morphology and structure of the materials, and tests their gas sensing performance. The test results show that compared to pure LaFeO₃ material, the gas sensing performance of Ni-doped LaFeO₃ material is improved in all aspects. Specifically, LFO-Ni2% exhibits a response as high as 102 towards 100 ppm of triethylamine at 190 °C, along with better selectivity and stability. Furthermore, the gas sensing mechanism is investigated. On one hand, doping with an appropriate proportion of Ni can lead to the formation of more-complete and smaller-sized microsphere structures with pores. This is beneficial for the adsorption of oxygen from the air onto the material surface, as well as for the diffusion of the target gas to the surface of the material, thereby enhancing gas sensitivity performance. On the other hand, the doped Ni enters the interior of the LaFeO₃ crystal, replacing some of the cations in LaFeO₃, increasing the concentration of charge carriers in the material, and reducing the material’s resistance. The sample can adsorb more oxygen, promoting the reaction between adsorbed oxygen and the target gas, and thereby improving the gas sensitivity performance of the sample. Full article

During the past decade, Gallium Oxide (Ga₂O₃) has attracted intensive research interest as an ultra-wide-bandgap (UWBG) semiconductor due to its unique characteristics, such as a large bandgap of 4.5–4.9 eV, a high critical electric field of ~8 MV/cm, and a high Baliga’s figure of merit (BFOM). Unipolar β-Ga₂O₃ devices such as Schottky barrier diodes (SBDs) and field-effect transistors (FETs) have been demonstrated. Recently, there has been growing attention toward developing β-Ga₂O₃-based heterostructures and heterojunctions, which is mainly driven by the lack of p-type doping and the exploration of multidimensional device architectures to enhance power electronics’ performance. This paper will review the most recent advances in β-Ga₂O₃ heterostructures and heterojunctions for power electronics, including NiO_x/β-Ga₂O₃, β-(Al_xGa_1−x)₂O₃/β-Ga₂O₃, and β-Ga₂O₃ heterojunctions/heterostructures with other wide- and ultra-wide-bandgap materials and the integration of two-dimensional (2D) materials with β-Ga₂O₃. Discussions of the deposition, fabrication, and operating principles of these heterostructures and heterojunctions and the associated device performance will be provided. This comprehensive review will serve as a critical reference for researchers engaged in materials science, wide- and ultra-wide-bandgap semiconductors, and power electronics and benefits the future study and development of β-Ga₂O₃-based heterostructures and heterojunctions and associated power electronics. Full article