查看更多>>摘要：? 2022 Elsevier B.V.In this work, nitrogen-doped graphene foam was synthesized by using hydrothermal routes. In the first step, graphene was synthesized by utilizing a modified Hummer's method and nitrogen-doped graphene foam was then synthesized at 180 °C by using an ammonia and graphene solution for 12 h. X-ray photon spectroscopy (XPS) was applied to determine the extent of doping by nitrogen on the graphene foam; three N-peaks were observed at 398.25, 399.69, and 401.46 eV, and XPS also showed that 6 at% of the synthesized graphene foam consisted of nitrogen atoms. The capability of this foam to absorb hydrogen was evaluated in a 6 M KOH solution through electrochemical impedance spectroscopy (EIS), galvanostatic charge/discharge, and cyclic voltammetry (CV) analysis. The hydrogen storage capacity of the achieved N-doped GF, showing the value of 1916.5 mAh.g?1 significantly improved in comparison to that of pure graphene in previous work, due to the increasing electronegative sites at the surface of the graphene foam.
查看更多>>摘要：? 2022 Elsevier B.V.The relationship between Zn content and room temperature (RT) mechanical properties of dilute Mg-xZn-0.1Ca (x = 0.1, 0.2,0.3, 0.5, 1.5, 2.5 in wt%) alloy sheets was investigated. The index Erichsen (IE) value, an indicator of stretch formability, was found to increase significantly from 6.6 mm to 8.4 mm by increasing the Zn content from 0.2 wt% to 0.3 wt%. Visco-Plastic Self-Consistent (VPSC) simulation revealed there was no apparent difference in the relative activity of deformation modes in Mg-0.2Zn-0.1Ca and Mg-0.3Zn-0.1Ca alloys. On the other hand, electron back-scattered diffraction observation showed that a component having basal poles tilted towards the transverse direction (TD) began to appear when 0.3 wt% of Zn was added, and the typical TD-split texture was developed when the Zn content was increased to more than 1.5 wt%. Therefore, the rapid improvement of RT formability observed in this study can be attributed to the formation of TD-split texture. In addition to this, the efficient scheme for parameter fitting required to use VPSC simulation was also proposed in this study.
查看更多>>摘要：? 2022 Elsevier B.V.Ni-rich layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM811) is one of the most promising cathode materials in advanced lithium-ion batteries. However, it suffers from poor cycling and rate capabilities due to the interfacial instability and structural degradation especially at high-voltage operation (＞4.3 V which are the key barriers for developing high-energy density cathode materials. Herein, we present an effective modification strategy toward the LiNi0.8Co0.1Mn0.1O2 through coating a rather uniform AZO protective layer on its surface, which can effectively passivate the deleterious side reactions at the cathode/electrolyte interface and improve structural stability of the layered oxides at 4.5 V high-voltage cycles. As a result, the AZO-modified Ni-rich cathode (AZO-NCM811) exhibits a great capacity retention of 86.3% after 100 cycles over 3.0–4.5 V at room temperature, which is superior than those for the pristine electrode (only 69.9%). Moreover, the AZO coating with a high ionic/electronic conductivity also endows LiNi0.8Co0.1Mn0.1O2 with a high-rate performance. This work provides a practical approach for developing the commercial application of Ni-rich cathode materials, more importantly, it may also be applied to resolve the interface instability issues occurring for other high-voltage cathode materials.
查看更多>>摘要：? 2022 Elsevier B.V.Porous carbon-based materials are among the most promising materials for future electrochemical energy storage and conversion and are sustainable and environmentally acceptable. The development of highly porous carbon compounds from biomass has become a popular topic of study. Herein, we report interconnected porous-structured carbon obtained from a biowaste precursor. Pine tree (Casuarina) seeds were carbonized by using 9 M concentrated sulfuric acid (H2SO4), and the obtained pine tree seed carbon (PTC) was activated by mixing various ratios with potassium hydroxide (1:1, 1:3, 1:5 ratio) and performing simple microwave pyrolysis. The pore size and surface area of the generated carbon could be fine-tuned. The surface area increased considerably as the KOH concentration increased, with an excellent specific surface area of 929.9 m2 g?1 (1:3 mass ratio). The synthesized porous carbon showed a high charge storage capacitance of 210 F g? 1 at 1 A/g, as well as remarkable capacitance retention after 10,000 charge/discharge cycles, even at a high current density. The remarkable electrochemical storage behaviour of hierarchically porous structured carbon networks is related to the optimal combination of micro- and mesoporous morphology with increased defect sites at the edges, which results in a higher surface area and enhanced conductivity.
查看更多>>摘要：? 2022 Elsevier B.V.A CoCrFeNiW0.2 metal-matrix composite (MMC) was fabricated by laser powder bed fusion (LPBF) and post-annealing, which exhibited comparable tensile ductility (44%) and yield strength (385 MPa) to as-casted CoCrFeNiW high entropy alloys with much higher W concentration. An Integrated Computational Materials Engineering (ICME) framework coupled with thermo-kinetic simulations was built to investigate the microstructure evolution and mechanical response of the as-fabricated and post-annealed MMCs. The combination of strength and ductility of the MMC can be attributed to the synergistic combination of dislocation, solid solution and grain boundary strengthening due to the multiple roles of W in the LPBF and post-annealing processes.
查看更多>>摘要：? 2022 Elsevier B.V.The effect of post annealing treatment on the phase transformation and the electrical properties of the sputtered hafnium oxide (HfO2) is investigated. As-deposited HfO2 films were annealed at 200 and 400 °C in ambient conditions. Film annealed at 200 °C is amorphous, but further annealing at 400 °C crystallizes it into the monoclinic structure. Amorphous films exhibit a higher bandgap (≥ 5.8 eV) than the monoclinic film (≈ 5.65 eV). The electrical characteristics of the Metal-Insulator-Metal devices reveal a nonlinear capacitance with respect to the voltage. The nonlinearity is predominant in the as-deposited film due to the oxygen vacancy related defects formed during the deposition. However, excess Hf-O bond formation occurs with annealing at higher temperatures, reducing the capacitance-voltage curve's nonlinearity. The dielectric constant of the as-deposited, 200, and 400 °C annealed films are estimated as 22.35, 22.64, and 20.57, respectively. The increment in the dielectric constant at 200 °C is due to its amorphous phase and reduced defects. Amorphous Si-In-Zn-O thin film transistors fabricated using the as-deposited and annealed hafnium oxide as gate insulator show almost similar threshold voltage of ≈ ?1 V. The transistor with hafnium oxide annealed at 200 °C shows the highest on current (1.04 × 10?6 A) followed by as-deposited (6.82 × 10?7 A) and 400 °C annealed device (5.86 × 10?7 A), respectively. Moreover, the interface state density increases monotonically from 3.98 × 1012 to 1.11 × 1013 cm?2 for as-deposited and 400 °C, respectively. The increment in the interface state density is due to the grain boundary formation due to the crystallization of HfO2.
查看更多>>摘要：? 2022 Elsevier B.V.The lack of research on low-frequency absorbing materials working at frequencies lower than 8 GHz makes it difficult to meet the military needs of the large wavelength electromagnetic shielding. In this study, crystalline and amorphous lithium zinc ferrites hollow microspheres (LiZn FHMs) were prepared by self-reactive quenching technology, based on Fe+Zn+Fe2O3 +O2 +Li2CO3 reactive system, using distilled water and 15 wt% NaCl solution as cooling medium, respectively. Effect of cooling medium on the formation mechanism and microwave absorption properties in low frequency range for two kinds of LiZn FHMs was studied. The results show that LiZn FHMs surface with distilled water as cooling medium has polygonal crystal structure. While the surface of LiZn FHMs is smooth by using 15 wt% NaCl solution, and XRD patterns prove that LiZn FHMs are of amorphous structures. When the cooling medium is changed from distilled water to NaCl solution, the magnetic loss of amorphous LiZn FHMs changes from double loss mechanism (natural resonance and eddy current loss) to a single loss mechanism (natural resonance). Compared with crystalline materials, the emergence of “rheology unit” and the change of magnetic loss mechanism are the main reasons for the improvement of microwave absorption properties in low frequencies. When the thickness of the amorphous sample is equal to 2 mm, the minimum reflectivity is ?29.8 dB, and the corresponding frequency is 7.1 GHz. The absorption frequency band below ?10 dB is 5.3–10.3 GHz, and its bandwidth is 5 GHz. This effectively meets the low frequency new absorbent “thin, light, wide and strong” demand, and it could be promising in the application of invisible coatings on the weapon equipments. The survival performances of weapon equipments in the complex electromagnetic field are expected to be improved.
查看更多>>摘要：? 2022 Elsevier B.V.L12-structured Ni3(Al, Ti) precipitates are promising strengthening particles in face-centered-cubic high entropy alloys (HEAs). However, if the Al/Ti ratio (R) is not carefully controlled, brittle intermetallic compounds can form, especially at the grain boundaries (GBs). In this study, a series of Ni35(CoCrFe)55AlxTi10?x HEAs with different R values, R = x/(10-x), were prepared, and the evolution of precipitates and their effects on the mechanical properties were investigated. The dispersed spherical precipitates within the grains act as an effective barrier to dislocation slip, producing high strength. However, increasing R (increasing Al) reduces the volume fraction of the precipitates within the grains, resulting in a decrease of yield strength. Both experimental measurements and first-principles calculations show that Al, Ti and Ni segregate to the GBs. This leads to the formation of L12 precipitates at the GB that, upon aging, coarsen to layer-like structures. When R ≥ 3 the local supersaturation of Al and Ti also leads to formation of a Heusler phase at the GBs, which reduces the ductility. However, when R > 3.5 the volume fraction of the Heusler phase decreases, and the plasticity increases again. These findings provide important guidance and inspire new strategies for the microstructural control in precipitate-strengthened HEAs.
查看更多>>摘要：? 2022 Elsevier B.V.The organic-inorganic halide perovskite (OIHP) materials are becoming promising, but there is still inherent defect-mediated-carrier recombination in hybrid perovskite materials, thus, leading to inefficient power conversion efficiency (PCE). The defect states, which act as the recombination centers, are usually formed during crystallization process. Here, by a hot injection method, Na2S ligand exchange is applied to synthesize copper indium selenium quantum dots (CuInSe2 QDs), which are well dispersed in N,N-dimethylformamide (DMF) and then added into perovskite precursor solution. The resulted QD-in-perovskite structure is found to be beneficial for enlarging grain size, and thus exhibits an improved crystallinity and absorption due to the passivation of trap states. Hence, the perovskite solar cell (PSC) based on the MAPbI3-CuInSe2 QD hybrid film show an improved carrier lifetime from 58.17 ns to 243.23 ns and an enhanced PCE from 16.3% to 18.4% due to higher open-circuit voltage, compared to the cell device based on the pure perovskite film. Additionally, the optimized cell device presents better stability, which can still keep 75% of the initial PCE after 20-day storage. Such a simple Na2S ligand exchange to introduce QD into perovskite provides strong potential for preparing other hybrid materials.
查看更多>>摘要：? 2022 Elsevier B.V.Photocatalytic treatment is a remarkable process that is popular for the degradation of several organic contaminants in wastewater. In this work, a series of graphitic carbon nitride/ZnTi-mixed metal oxide (CN/ZnTi-MMO) composites were prepared as photocatalysts through simple calcination. The CN-MMO samples were characterized and applied for photocatalytic degradation of ciprofloxacin (CIP), which is an antibiotic model pollutant. The optimized CN/ZnTi-MMO composite showed complete degradation of CIP within 20 min, leading to a rate constant that is approximately 6 times that of pristine CN and 7 times that of ZnTi-MMO. The increase in the degradation rate of the optimized CN/ZnTi-MMO composite was attributed to the excellent separation and transportation of photogenerated electron-holes pairs, as proven by the photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the energy-resolved distribution of the electron trap (ERDT) pattern of the composite sample suggests the formation of an interfacial electron trap state due to interfacial contraction in the composite, resulting in the excited electrons being trapped and avoiding charge recombination. Based on the optical properties, ERDT results, and activity test, a photocatalytic degradation mechanism of CIP over a CN/ZnTi-MMO composite was proposed. Additionally, the degraded solution showed less bio-toxicity than the original CIP solution. Thus, the CN/ZnTi-MMO composite can be employed as a potential visible-light-driven photocatalyst for the detoxification of pharmaceutical wastewater.
NSTL
Elsevier