查看更多>>摘要：Although Si is a promising anode material for lithium-ion batteries, scalable synthesis of Si anodes with high cyclability and low swelling remains a significant challenge. Herein, we describe the electrochemical fabrication of a Si@graphite@SiC composite anode from a SiO_2/graphite mixture via an electro-deoxidation-based molten salt process. The exfoliated graphite enhances the electrical conductivity of the composite and cushions the volume expansion of Si nanowires, while the SiC component acts as an active matrix that accommodates the expansion of the Si during lithiation. This significantly increases the electrode cycle life. In half-cell testing, the composite exhibited 80% capacity retention until 500 cycles. It showed good cycling performance even at a high areal capacity of 4.6 mAh/cm~2. Further, a full cell comprising the composite anode and a LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 cathode possessed a high capacity and demonstrated 84% capacity retention after 70 cycles. This work provides new insights into the rational design of alloy anodes for high-energy density batteries.
查看更多>>摘要：To recover the remanence (or maximum energy product ((BH)_(max))) and squareness with high coercivity in diffusion-processed hot-deformed Nd-Fe-B magnets, new efforts have been made in this work. Annealing at a selected temperature of 800 °C under pressure was applied to the hot-deformed magnets diffused by the Nd_(70)Cu_(30) or Nd_(70)Cu_(15)Ga_(15) alloy. After this process, the thick powder boundary phase dissolved in the matrix and diffused into the intergranular regions. The c-axis misalignment of Nd_2Fe_(14)B grains near the diffusion surface was significantly improved, leading to increased remanence by 0.10-0.18 T and (BH)_(max) by 47-85 kj/m~3 in the two diffusion-processed magnets. The distribution of the powder boundary phase, the proportions of the intergranular Nd-rich phase, the c-axis alignment of grains and the grain sizes from the diffusion surface to the center of the magnets tend to be relatively uniform. The squareness factor of the demagnetization curve increased from 0.89 to 0.95 for the Nd_(70)Cu_(30)-diffused magnet and from 0.85 to 0.93 for the Nd_(70)Cu_(15)Ga_(15)-diffused magnet after the process, returning to the level of the as-deformed magnet. Microstructure analysis and micromagnetic simulations indicate that the improved squareness factor is due to the homogeneous magnetization reversal process caused by the homogeneous microstructure.
查看更多>>摘要：A series of NaYF_4:0.2Yb/0.02Ho microcrystals co-doped with various K~+ and Gd~(3+) concentrations were synthesized by hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and upconversion (UC) spectroscopy were used to study the effects of co-doped ions on the phase structure, morphology, size and up-conversion luminescence (UCL) properties of microcrystals in detail. The results show that the K~+ and Gd~(3+) co-doping do not evoke the change in crystal structure, but the UCL intensities of NaYF_4:0.2Yb/0.02Ho are significantly enhanced. Compared to K~+ and Gd~(3+)-absent sample, UCL intensities of green emission (541 nm) and red emission (643 nm) in NaYF_4:0.2Yb/0.02Ho microcrystals via 15 mol% K~+ and 15 mol% Gd~(3+) co-doping are increased by 2.4 times and 3.3 times, respectively. The temperature sensing characteristics and thermal quenching properties of the microcrystals were also explored. Significantly, the maximum relative sensitivity of the studied sample reaches 0.0127 K~(-1) at 298 K, which indicates that NaYF_4:0.2Yb/0.02Ho phosphors can be suitable for temperature sensing.
查看更多>>摘要：Cubic spinel Li_4Ti_5O_(12) is a desired anode material for lithium-ion batteries (LIBs) due to high stability (the feature of "zero strain") and good safety. Moreover, Li_4Ti_5O_(12) has a good affinity with sulfur for restraining lithium polysulfides (LiPSs) by the Ti-S bond in lithium-sulfur batteries (LSBs). Interestingly, extra cobalt element is introduced to form Li_2CoTi_3O_8, which not only increases theoretical capacity for LIBs but also enhances the adsorption of sulfur for LSBs. In this paper, Li_2CoTi_3O_8 nanoparticles are synthesized via a sol-gel method. As the anode for LIBs, Li_2CoTi_3O_8 displays a desired specific capacity (335.3 mAh g~(-1) at 0.2 A g~(-1)) and a better rate-capability (188.5 mAh g~(-1) at 5 A g~(-1); no capacity decay over 400 cycles), which is superior to electrochemical performances of the reported same substances. Besides, Li_2CoTi_3O_8 nanoparticles are designed as both the sulfur host material and the modified separator in LSBs for the first time. Under the LCTO-coated separator, the Li_2CoTi_3O_8/S electrode achieves a first capacity of 1048 mAh g~(-1) at 0.5 C and the stable capacity retention (732.7 mAh g~(-1) after 100 cycles). The enhanced performance of the Li_2CoTi_3O_8 electrode is the result of synergistic effect of dispersed particles and larger contact area for LIBs and LSBs.
查看更多>>摘要：Copper Nitride (Cu_3N) thin films exhibit promising optoelectronic properties and are favourable for further applications in the field of photodetection, lithium-ion batteries etc. In this work, Cu_3N thin film deposited by reactive High-Power Impulse Magnetron Sputtering (HiPIMS) and used for photodetection application for the first time. The microstructure of Cu_3N nanocrystal shows the uniform crystalline morphology and less defects due to high target species ionization rate. The phase structure analysis results confirmed the presence of nitrogen within Cu_3N thin film that is composed of Cu_3N crystallites with anti-ReO_3 structure. Remarkably, optical properties reveal significant absorbance and enhancement in ultraviolet (UV) and visible (Viz) range, which strongly affect the photodetection properties of fabricated ITO/Cu_3N/ITO device. Excellent photosensitivity of 3792% was attained with a fixed light intensity. Furthermore, the photosensitivity was increased to 7443% with increased light intensity. It was perceived that the enhanced surface properties and perfect formation of ITO/Cu_3N/ITO resulted in beneficial pn junction thus exhibits high performance and ultrafast electron-hole recombination. Also, the HiPIMS technique offers high-quality films with a dense and smooth surface that helped in enhancing photodetection. These outstanding results emanate Cu_3N films could be potential candidate for future optoelectronic devices fabrication that can be applied in smart thin-film gadgets.
Mahmoud A. HefnawySahar A. FadlallahRabab M. El-Sherif
14页
查看更多>>摘要：In the present work, Cu-doped NiO is fabricated and synthesized using a microwave-assisted sol-gel method using different Ni and Cu precursors ratios supported on commercial graphite rod (G) and examined as an efficient electrocatalyst toward urea electrochemical oxidation (UEO). The morphology and chemical structure of the prepared electrocatalysts is confirmed by XRD, XPS, and SEM techniques. The catalytic activity of the prepared materials is measured and examined toward UEO as a function of current density and compared with different Ni-based catalysts in NaOH solution using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The oxidation current density of G/Ni_(0.9)Cu_(0.1) reached 32 mA cm~(-2) and its onset potential of urea oxidation peak is shifted from 0.43 V (vs. Ag/ AgCl) in NiO catalyst to 0.40 V (vs. Ag/AgCl) for G/Ni_(0.9)Cu_(0.1). The charge transfer resistance for different modified surfaces at various conditions (e.g., urea concentration, electrolyte concentration, and oxidation potential) is measured using the electrochemical impedance spectroscopy (EIS). The CO tolerance is studied using the DFT method to prove the stability of the electrodes and the performance efficiency due to Cu atoms dopping into NiO crystal. The adsorption of CO is studied upon Cu-doped NiO and compared with pristine NiO alloy at different adsorption sites- top and hallow.
查看更多>>摘要：Dye-sensitized solar cells (DSSCs) with TiO_2 as electron transport layer (ETL) demonstrate great potential in the field of photoelectric devices featuring low cost and high power conversion efficiency (PCE). However, the photovoltaic performance of DSSCs based on TiO_2 ETL is still confined by the undesirable charge recombination occurring in TiO_2 layer (intrinsic defects), dye layer (self-quenching) and at the interface between TiO_2 and electrolyte (back electron transfer). Herein, we firstly adopted a trisiloxane molecule (denoted as TSi) to holistically reduce the abovementioned charge recombination of DSSCs via passivating surface defects of TiO_2, fine-tuning dye molecules arrangement and forming interfacial energy barrier. As a result, the Z907-based DSSCs with TiO_2/TSi ETL deliver a high PCE of 9.43%, increasing over 16% than that of DSSCs without TSi treatment. Meanwhile, the DSSCs based on TiO_2/TSi ETL present stronger endurance to high humidity and better long-term stability versus that of the DSSCs without TSi treatment. Our work provides a simple yet effective strategy to holistically reduce charge recombination of devices for improving the photovoltaic performance and stability of DSSCs.
查看更多>>摘要：La-doped CeO_2 nanoparticles of composition Ce_(1-x)La_xO_(2-δ) (0 ≤ x ≤ 0.1) have been studied here as prospective electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs). They were synthesized by auto-combustion method and the powder samples were calcined at 700 °C to get ultrafine nanocrystalline particles. They were characterized by XRD, Raman, FTIR, XPS, DRS, FESEM/EDX, particle size analyzer and ac-impedance techniques. Ionic conductivity was measured from 350 - 750 °C. The Ce_(0.90)La_(0.10)O_(2-δ) (0.1 LDC) and Ce_(0.95)La_(0.05)O_(2-δ) (0.05 LDC) showed a maximum conductivity of 8.89 ×10~(-3) and 8.32 ×10~(-3) S cm~(-1) at 700 °C, respectively. The σt of 0.1 LDC = 1.01 ×10~(-2) S cm~(-1) at 750 °C. The activation energy of 0.1 LDC and 0.05 LDC was found to be 0.70 eV and 0.87 eV, respectively. These values are higher than those reported for La-doped CeO_2 in literature. The SOFC performance with 0.05 LDC as electrolyte showed open circuit voltage of 0.81 V and maximum power density of 41 mW cm~(-2) at 650 °C using hydrogen as fuel.
查看更多>>摘要：High entropy alloys (HEAs) have attracted considerable attention due to their excellent mechanical properties, which provides new insights for designing next generation structural materials. A series of Al_(0.2)Co_(1.5)CrFeNi_(1.5)Ti_(0.5)B_x (x = 0, 0.15, 0.3, 0.45, 0.6, 0.75 and 0.9, in molar ratio) HEAs was prepared by vacuum arc melting to investigate the effect of boron doping on the phase evolution, microstructure transformation and mechanical properties. The results indicated that the HEAs with trace boron doping (x = 0.15) maintained single FCC phase, while it evolved to FCC phase, in-situ borides (TiB_2 and Cr_2B) and Laves phase when the boron molar ratio higher than 0.3. With the boron molar content increased from 0 to 0.9, the microstructures of the HEAs transformed from complete dendrite to dendrites, irregularly shaped TiB_2, needle-shaped Cr_2B and lamellar eutectic structure which composed by alternate layers of FCC phase and Laves phase. B doping improved the strength and hardness of the HEAs. The enhanced mechanical properties of the boron doped HEAs was attributed to the synergistic strengthening effect among interstitial solid solution strengthening, second phase strengthening, dislocation strengthening, fine grain strengthening and heterostructure strengthening.
查看更多>>摘要：The configurations of nitrogen species have a crucial influence on the transition metal-nitrogen-doped carbon catalysts (M-N-C). Whereas, how to build more sp2 hybrid N (including pyridinic and graphitic N) to enhance the catalytic activity and charge transfer rate of the carbon-based ORR catalysts remains a challenge. Herein, Co-embedded nitrogen-enriching platanus bark-derived porous carbon (PBPC) material (Co-N-C) was developed from the pyrolytic platanus bark, assisted by impregnating cobalt salt and ethylene-diamine nitriding strategy. The synthesized catalyst exhibits a high nitrogen content of 5.02%, of which over 2/3 are high conductivity sp2 hybrid N (consist of pyridinic and graphite-N), suggesting the unity of high activity and conductivity. Thus, it delivers a competitive half wave potential and a lower Tafel slope (69.55 mV dec~(-1)) than Pt-C-20% catalyst. The ZAB with Co-N-C-900 catalyst exhibits a higher open-circuit potential and a peak power density up to 3.5 times (186.17 mW cm~(-2)) higher than that of the Pt-C-20%. During the durability test for 100 cycles (16.7 h), the voltage gap only increased by 4.2%, nevertheless, the Pt-C-20%-based ZAB encountered a catastrophic polarization surge in less than 16 h. When assembling a flexible ZAB, it performs excellent flexibility in bending tests, and the voltage gap merely increased by 1.7% after 100 cycles (16.7 h).
NSTL
Elsevier