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1.
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.  相似文献   
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3.
Transition metals sulfide-based nanomaterials have recently received significant attention as a promising cathode electrode for the oxygen evolution reaction (OER) due to their easily tunable electronic, chemical, and physical properties. However, the poor electrical conductivity of metal-sulfide materials impedes their practical application in energy devices. Herein, firstly nano-sized crystals of cobalt-based zeolitic-imidazolate framework (Co-ZIF) arrays were fabricated on nickel-form (NF) as the sacrificial template by a facile solution method to enhance the electrical conductivity of the electrocatalyst. Then, the Co3S4/NiS@NF heterostructured arrays were synthesized by a simple hydrothermal route. The Co-ZIFs derived Co3S4 nanosheets are grown successfully on NiS nanorods during the hydrothermal sulfurization process. The bimetallic sulfide-based Co3S4/NiS@NF-12 electrocatalyst demonstrated a very low overpotential of 119 mV at 10 mA cm?2 for OER, which is much lower than that of mono-metal sulfide NiS@NF (201 mV) and ruthenium-oxide (RuO2) on NF (440 mV) electrocatalysts. Furthermore, the Co3S4/NiS@NF-12 electrocatalyst showed high stability during cyclic voltammetry and chronoamperometry measurements. This research work offers an effective strategy for fabricating high-performance non-precious OER electrocatalysts.  相似文献   
4.
The development of efficient and stable electrocatalysts is of great significance for improving water splitting. Among them, transition metal oxyhydroxides show excellent performance in oxygen evolution reactions (OER), but there are certain difficulties in direct preparation. Recently, Metal–organic frameworks (MOFs) as precatalysts or precursors have shown promising catalytic performance in OER and can be decomposed under alkaline conditions. Therefore, using a mild and controllable way to convert MOFs into oxyhydroxides and retaining the original structural advantages is crucial for improving the catalytic activity. Herein, a rapid electrochemical strategy is used to activate well-mixed MOFs to prepare Co/Ni oxyhydroxide nanosheets for efficient OER catalysts, and the structural transformation in this process was investigated in detail by using scanning electron microscope, X-ray diffraction, Raman, X-ray photoelectron spectroscopy and electrochemical methods. It is discovered that electrochemical activation can promote ligand substitution of well-mixed MOFs to form porous oxyhydroxide nanosheets and tune the electronic structure of the metal (Co and Ni), which can lead to more active site exposure and accelerate charge transfer. In addition, the change of structure also improves hydrophilicity, as well as benefiting from the strong synergistic effect between multiple species, the optimal a-MCoNi–MOF/NF has excellent OER performance and long-term stability. More obviously, the porous CoNiOOH nanosheets are formed in situ during electrochemical activation process through structural transformation and acts as the active centers. This work provides new insights for mild synthesis of MOFs derivatives and also provides ideas for the preparation of highly efficient catalysts.  相似文献   
5.
This work investigates selective Ni locations over Ni/CeZrOx–Al2O3 catalysts at different Ni loading contents and their influences on reaction pathways in ethanol steam reforming (ESR). Depending on the Ni loading contents, the added Ni selectively interacts with CeZrOx–Al2O3, resulting in the stepwise locations of Ni over CeZrOx–Al2O3. This behavior induces a remarkable difference in hydrogen production and coke formation in ESR. The selective interaction between Ni and CeZrOx for 10-wt.% Ni generates more oxygen vacancies in the CeZrOx lattice. The Ni sites near the oxygen vacancies enhance reforming via steam activation, resulting in the highest hydrogen production rate of 1863.0 μmol/gcat·min. In contrast, for 15 and 20-wt.% Ni, excessive Ni is additionally deposited on Al2O3 after the saturation of Ni–CeZrOx interactions. These Ni sites on Al2O3 accelerate coking from the ethylene produced on the acidic sites, resulting in a high coke amount of 19.1 mgc/gcat·h (20Ni/CZ-Al).  相似文献   
6.
High-temperature water electrolysis through solid oxide electrolysis cells (SOEC) will play a key role in building a hydrogen economy in the future. However, the delamination between the air electrode and the electrolyte remains a critical issue to be addressed. Previously, it was hypothesized that Co migration may improve the catalytic activity of the SrZrO3 second phase at the LSCF-YSZ interface, eventually leading to the delamination. In this work, the LSCF-YSZ interfaces sintered at different temperatures were examined in detail. The activation behaviors of the LSCF electrodes upon application with electrolysis current were characterized under different conditions. Further, samples containing purposely added SrZrO3 interlayer with and without cobalt were fabricated and compared. The activation process is less significant for the sample with cobalt-added SrZrO3 interlayer than the sample with pure SrZrO3 layer, supporting the hypothesis that Co migration may lead to the activation behavior.  相似文献   
7.
Mg-based hydride is a promising hydrogen storage material, but its capacity is hindered by the kinetic properties. In this study, Mg–Mg2Ni–LaHx nanocomposite is formed from the H-induced decomposition of Mg98Ni1·67La0.33 alloy. The hydrogen capacity of 7.19 wt % is reached at 325 °C under 3 MPa H2, attributed to the ultrahigh hydrogenation capacity in Stage I. The hydrogen capacity of 5.59 wt % is achieved at 175 °C under 1 MPa H2. The apparent activation energies for hydrogen absorption and desorption are calculated as 57.99 and 107.26 kJ/mol, which are owing to the modified microstructure with LaHx and Mg2Ni nanophases embedding in eutectic, and tubular nanostructure adjacent to eutectic. The LaH2.49 nanophase can catalyze H2 molecules to dissociate and H atoms to permeate due to its stronger affinity with H atoms. The interfaces of these nanophases provide preferential nucleation sites and alleviate the “blocking effect” together with tubular nanostructure by providing H atoms diffusion paths after the impingement of MgH2 colonies. Therefore, the superior hydrogenation properties are achieved because of the rapid absorption process of Stage I. The efficient synthesis of nano-catalysts and corresponding mechanisms for improving hydrogen storage properties have important reference to related researches.  相似文献   
8.
Hydrogen technology is widely considered a novel clean energy source, and electrolysis is an effective method for hydrogen evolution. Therefore, efficient hydrogen evolution reaction (HER) catalysts are urgently needed to replace precious metal catalysts and meet ecological and environmental protection standards. Herein, Ni–Mn–P electrocatalysts are synthesized using facile electrodeposition technology. The influence of the Mn addition on the catalytic behavior is studied by the comprehensive analysis of catalytic performance and morphology of the catalysts. Among them, the Ni–Mn–P0.01 catalyst exhibits small coral-like structures, greatly improving the adsorption and desorption of hydrogen ions and reducing the overpotential hydrogen evolution. Consequently, overpotential at 10 mA cm?2 electric current density is 113 mV, and the value of the Tafel slope achieves 74 mV/dec. Furthermore, the Ni–Mn–P catalyst shows long-time (20 h) stability at current densities of 10 and 60 mA/cm2. The results confirm that the synergistic effect of Ni, Mn, and P accelerates the electrochemical reaction. Meanwhile, the addition of manganese element can change the micromorphology of the catalyst, thereby exposing more active sites to participate in the reaction, enhancing water ionization, improving the catalytic performance. This study opens a new way toward improving the activity of the catalyst by adjusting Mn concentration during the electrodeposition process.  相似文献   
9.
Today, utility meters for water are tested for measurement behavior at stable operating conditions at specified flow rates as part of the approval process. The measurement error that occurs during start and stop or when changing between flow rates may not be taken into account. In addition, there are new technologies whose measuring behavior under real-world conditions is only known to a limited extend. To take these facts into account, a new method has been developed and tested to determine the measurement behavior of water meters under dynamic load profiles as they occur in the real application. For this purpose, a test rig for flow rate measurement was extended by a cavitation nozzle apparatus and the generation of dynamic load profiles was validated. For the cavitation nozzles used, possible factors influencing the flow rate, such as temperature and purity of the water as well as the upstream pressure were investigated. Using different types of domestic water meters, the applicability of the dynamic test procedure was demonstrated and the measurement behavior of the meters was characterised.  相似文献   
10.
《Ceramics International》2022,48(14):20158-20167
Vacuum induction melting is a potential process for the preparation of TiAl alloys with good homogeneity and low cost. But the crucial problem is a selection of high stability refractory. In this study, a BaZrO3/Y2O3 dual-phase refractory was prepared and its performance for melting TiAl alloys was studied and compared with that of a Y2O3 refractory. The results showed the dual-phase refractory consisted of BaZr1-xYxO3-δ and Y2O3(ZrO2), exhibited a thinner interaction layer (30 μm) than the Y2O3 refractory (90 μm) after melting the TiAl alloy. Although the TiAl alloys melted in the dual-phase and Y2O3 refractory exhibited similar oxygen contamination (<0.1 wt%), the alloy melted in the dual-phase refractory had smaller Y2O3 inclusion content and size than that in the Y2O3 refractory, indicating that the dual-phase refractory exhibited a better melting performance than the Y2O3 refractory. This study provides insights into the process of designing highly stable refractory for melting TiAl alloys.  相似文献   
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