查看更多>>摘要：? 2022 Elsevier B.V.Carbon materials are commonly used as electrocatalyst supports in fuel cells. Nevertheless, carbon corrosion is a severe concern under strong acidic and oxidizing environments. Hence, developing a robust catalyst support is critical to ensuring fuel cells stability. Herein, we report a unique support of few-layered nitrogen-doped graphene wrapped three-dimensional (3D) flower-like anatase TiO2 (TiO2@N-Gr) via in-situ polymerizing dopamine on the surface of a 3D-TiO2 flower precursor, followed by pyrolysis. After loading Pt nanoparticles, Pt-TiO2@N-Gr-800 exhibits comparable ORR activity to the commercial Pt/C catalyst (E1/2 = 0.91 VRHE), superior stability in a 30 K cycling stability test and strong CO resistance capability. The outstanding performance of the Pt-TiO2@N-Gr-800 catalyst is attributed to the strong anti-corrosion property and high electronic conductivity of the nanocomposite support, as well as a strong metal and support interaction. The unique flower-like scaffold is also of great advantage for mass transfer. This work provides a facile strategy to synthesize robust nanocomposite supports for fuel cells.
查看更多>>摘要：? 2022 Elsevier B.V.Proton-conducting oxides are potential materials for electrochemical devices such as fuel cells, hydrogen pumps, hydrogen sensors, and the tritium purification and recovery system in nuclear fusion reactors. The hydrogen concentration in oxide materials is important, but its precise measurement is difficult. In this study, thermal desorption spectroscopy (TDS) was used to investigate hydrogen dissolution and release behavior in three zirconates, BaZr0.9Y0.1O3-α (BZY), BaZr0.955Y0.03Co0.015O3-α (BZYC), and CaZr0.9In0.1O2.95 (CZI) in the temperature range of 673–1273 K using deuterium (D2) (1.33 kPa) and heavy water (D2O) (2.8 kPa, saturated pressure at room temperature). To compare the experimental results of the D2 and D2O desorption profiles derived by TDS analysis, the simulation code of the tritium migration analysis program, version 4 (TMAP4) was employed. From TDS measurement, a similar trend of temperature-dependent hydrogen solubility was obtained for all samples compared to the literature data of HT- and DTO-exposed samples using a tritium imaging plate (TIP) method. A higher amount of hydrogen was dissolved in both BZY and BZYC under D2O exposure at 873 K, and the highest amount was found for BZYC. In most of the cases, the hydrogen diffusivities calculated by TMAP4 were higher than the experimental values, because oxygen is not considered a diffusion species in TMAP4.
查看更多>>摘要：? 2022 Elsevier B.V.As an environmentally friendly thermoelectric material, SnSe has attracted great attention because of its excellent performance in its single-crystal form. On the other hand, the better mechanical property and lower manufacturing cost of its polycrystalline counterpart with the better mechanical property and lower manufacturing cost can serve as a better candidate for widespread applications. Previous reports on p-type polycrystalline SnSe mainly focus on optimizing the carrier concentration by doping alkali metals or decreasing the lattice thermal conductivity by nanostructuring. Here, we report the effect of Yb doping on the thermoelectric properties of polycrystalline SnSe prepared by solvothermal synthesis. Through introducing Yb, the p-type carrier concentration is increased and the density of states at valence band maximum is distorted, which is revealed by DFT calculation, leading to an increase of the effective mass. Thus, the power factor has been markedly enhanced to 0.78 mW m?1 K?2 at 823 K (about 1.6 times that of undoped SnSe). Moreover, Yb doping in SnSe decreases the lattice thermal conductivity by intensifying the phonon scattering. As a result, a high zT of 1.1 at 823 K in Sn0.98Yb0.02Se is achieved along the in-plane direction. This work provides a new way for improving the thermoelectric properties of SnSe by modifying its valence band structure.
查看更多>>摘要：? 2022 Elsevier B.V.Inspired by the superior thermoelectric performance of two-dimensional (2D) materials, the electrical transport and thermoelectric properties of honeycomb-like puckered PbTe monolayer were theoretically evaluated using the first-principles calculations and the semiclassical Boltzmann transport theory. The puckered PbTe monolayer is a direct gap semiconductor with wide bandgap of 2.251 eV within Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional in combination with spin-orbital coupling (SOC) effect. Further analysis of formation energy, elastic constant, and ab initio molecular dynamics (AIMD) simulation prove the thermodynamic, mechanical and thermal stabilities of PbTe monolayer. The low thermal transport, small phonon group velocity, large Grüneisen parameters, and short phonon relaxation time greatly suppress the phonon transport and lead to low lattice thermal conductivity of ～0.75 and ～0.79 W/m K along the armchair and zigzag directions at 900 K, respectively. An optimal ZT = ~1.55 at the carrier concentration of 3.94 × 1012 cm?2 is obtained for PbTe monolayer along zigzag direction at 900 K, which demonstrates the great advantages of honeycomb-like puckered PbTe monolayer as promising n-type thermoelectric material. Our present results would not only provide fundamental understanding of thermoelectric transport in honeycomb-like puckered PbTe monolayer, but also shed some light on the theoretical design of low dimensional PbTe-layered nanomaterials in thermoelectric applications.
查看更多>>摘要：? 2022 Elsevier B.V.Aimed at the bottleneck problem in conventional gas sensors that the effective detection of CO2 gas can only be accomplished at concentrations above thousands of ppm and higher operating temperature, in this work, microstructured ZnSnO3 equipped with rambutan-like hexahedral features with the hollow interior was successfully synthesized through a facile one-step hydrothermal method. Visible light was utilized as an excitation source to further enhance the sensing property. The investigation elaborated that at optimum hydrothermal time of 16 h, ZnSnO3 showed a high gas response (~4.65), repeatability, and long-term stability towards 400 ppm CO2 at room temperature. The response under purple light was 3.5 times higher than that under dark conditions, resulting from photoelectrons' generation. Furthermore, ZnSnO3 sensor had excellent selectivity to 50 ppm CO2. The large specific surface area and abundant oxygen vacancies of ZnSnO3 contribute to the excellent gas-sensing performance, which addresses the dilemma that it is difficult to break through the energy barrier through surface interaction to impact the band structure and carrier concentration because CO2 is a non-polar molecule formed by polar bonds. Therefore, ZnSnO3 is a promising material for the development of devices utilized in medical respiratory detection, agricultural crop growth detection and other fields.
查看更多>>摘要：? 2022 Elsevier B.V.Nanocrystalline holmium orthoferrite (HoFeO3) was synthesized by the chemical sol-gel technique. The main focus of attention was to explore the behavior of nanocrystalline system of HoFeO3 in the context of multiferroicity. Structural investigation by observing X-ray diffractograms and its thorough Rietveld analysis was carried out in detail which confirms the deviation in crystallographic structure. Structural study confirms the pure orthorhombic (Pnma) phase of HoFeO3 with zero impurity including the presence of uniform particle size distribution in the nano regime. Different useful structural parameters were also calculated from this theoretically generated pattern, which help to understand the magnetoelectric behavior explored in the sample. Surface morphology studied by FESEM micrographs confirmed a more or less uniform grain distribution in nano regime. EDAX spectra and mapping confirms the elemental purity. Thermal variation of magnetization measurements of HoFeO3 was carried out under zero-field cooled and field (~200 Oe) cooled conditions. Also, variation of magnetization with field (MH Loop) yields the presence of magnetic ordering with a relatively high value of magnetization compared to its corresponding bulk counterpart. During field-variation, magnetization value wasn't yet saturated even at the maximum applied field of ~3 T, indicating the presence of magnetic ordering and superparamagnetism. Detailed high-temperature dielectric study including thermal variation, as well as frequency variation of dielectric constant together with related electric parameters provide various important information like ferro to para transition temperature, etc. These observations and various analyzes including Cole-Cole analysis of frequency variation of permittivity, Nyquist plot impedance analysis, etc. provide all dielectric parameters which are essential to understand the dielectric properties of the sample. The studies of ferroelectric loop and presence of room temperature magnetoelectric coupling suggest type-II multiferroicity of the present system of HoFeO3, which is usually not found in the bulk system. Presence of prominent remnant polarization with feeble dielectric loss and substantial magnetization clearly establishes the multiferroic candidature of nanocrystalline HoFeO3. This signature of multiferroicity will definitely strengthen the quality of application of the sample in M-E devices.
查看更多>>摘要：? 2022 Elsevier B.V.Negative thermal expansion particles can compensate metal matrix composites to achieve near-zero thermal expansion materials. However, there are huge thermal residual mismatch stresses in the particles due to the thermal expansion mismatch between matrix and reinforcement. The use of hybrid reinforcement is required to solve the stress concentration problem. In this study, the hybrid Al matrix composites reinforced with ZrW2O8 and SiC reinforcements (SiCp, SiCnw) were fabricated by the pressure infiltration process. The effect of SiC content on microstructure, phase composition, thermal expansion and mechanical properties were examined by a combination of XRD, SEM, thermal dilatometer and bending tests. The results showed that the high-pressure phase (γ-ZrW2O8) content of hybrid metal matrix composites decreased with increasing SiC fraction. Among them, the composites containing 61.7 vol%ZrW2O8 and 3.3vol%SiCnw achieved the best performance with a bending strength of 100–150 MPa and a near-zero thermal expansion (2.0–3.0 ×10–6K?1) in a wide range of ? 50–120 °C, which was attributed to the synergetic hybrid effects of SiCnw and ZrW2O8. This work opens up a new frontier for the design and preparation of lightweight zero-thermal expansion materials.
查看更多>>摘要：? 2022 Elsevier B.V.Sandwich microstructure composites composed of Ce2Fe17N3-δ and different mass fractions of expanded graphite (0, 1, 2, 3 wt%) were prepared, and their microwave absorption properties were studied. The microscopic morphology, composition, soft magnetic properties, chemical structure, electromagnetic parameters, and absorption properties of the Ce2Fe17N3-δ/EG composites were analyzed. The results show that Ce2Fe17N3-δ is an irregular particle with an average particle size of about 3 μm and EG is a multi-layer structure with an average interlayer spacing of about 2.7 μm. The saturation magnetization (Ms) value of Ce2Fe17N3-δ is 135 emu/g, and the coercivity (Hc) is 53 Oe. The effect of the loading of expanded graphite in the Ce2Fe17N3-δ/EG composites on their microwave absorbing properties is discussed. It was found that the well-designed two-component and appropriately loaded expanded graphite endowed the Ce2Fe17N3-δ/EG composites with excellent absorption properties. When the mass fraction of expanded graphite was 1% and the thickness of the absorber was 1.42 mm, the reflection loss reached ?67.3 dB at 14.9 GHz with an effective bandwidth of 5.74 GHz. Compared with other expanded graphite-based absorbing materials, Ce2Fe17N3-δ/EG composites exhibited better electromagnetic wave absorption performance at a lower thickness. The enhancement of the absorption performance is attributed to the optimization of impedance matching and the synergistic action between multiple loss mechanisms.
查看更多>>摘要：? 2022 Elsevier B.V.The effects of trace transition elements (Mn, Cr, V) on the solidification microstructure and the thermal conductivity of Al-9Si based alloys have been investigated. It was found that the effect of Mn, Cr, V on the solidification behavior and solidification microstructure is mainly related to α-Al grains via affecting heterogeneous nucleation and growth restriction, while no significant effect on the solidification behavior and microstructure of eutectic Si was observed. Compared with factors including grain size of α-Al and morphology characteristics (e.g. size, spacing, and shape factor) of eutectic Si, the solid solubility in Al matrix is confirmed to be one of the most important factors affecting thermal conductivity. Due to the larger partition coefficient of V compared with Cr and Mn, the solid solubility and the lattice distortion of α-Al in Al-9Si-xV alloy were increased significantly, thus the thermal conductivity of alloy was decreased steeply from 171.7 to 152.3 W/m·K with the content of V increasing from 15 to 1010 ppm. A linearly fitted curve reflecting the relationship between the content of the transition elements and the thermal conductivity of alloys has been proposed, which can be used to optimize the alloy composition in subsequent remelting or recycling process. Furthermore, two thermal conductivity models (H-S model and Maxwell model) also have been used to evaluate the effect of Mn, Cr, V on thermal conductivity, in which the thermal conductivity of α-Al was corrected based on the measured solid solubility. In this way, the data correlation between the experimental and fitted value based on H-S model and Maxwell model is increased from 0.18 to 0.96. These obtained results could be helpful to precisely control the composition and further improve the thermal conductivity of Al-Si based alloy during the primary production and / or recycling process.
查看更多>>摘要：? 2022 Elsevier B.V.ABy compounds with superlattice structures are considered as new generation materials for hydrogen storage and very promising as negative electrode for Ni-MH batteries. These compounds can be considered as the stacking of two fundamental layers along the c crystallographic axis: [A2B4] and [AB5]. Binary RNix (R = rare earths) compounds adopting stacking structures absorb large quantity of hydrogen but show poor reversibility. The superlattice structures are built by constraining the ab planes of the [A2B4] subunit to that of the more stable [AB5] one. The volume mismatch between the two subunits is the main cause of the multi-plateau behavior of the binary RNix (R = rare earths) compounds. The multi-element compounds show often improved hydrogen storage properties. In this review we highlight the structural evolution with the element substitution and the correlation between the subunit volume matches and the hydrogenation properties.
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