The effects of sulfur doping on the performance of O3-Li0.7[Li1/12Ni1/12Mn5/6]O2 powder

Li_0.7[Li_1/12Ni_1/12Mn_5/6]O₂ and Li_0.7[Li_1/12Ni_1/12Mn_5/6]O_2-yS_y (y=0.1, 0.2, 0.3) powders were synthesized by using a sol-gel method. As-prepared samples showed typical rhombohedral O3 layered structure. The shape of the initial discharge curve for the samples was almost equal to that of the layered structure. However, the electrode materials were transferred from layered to spinel structures with cycling. At the first cycle, Li_0.7[Li_1/12Ni_1/122Mn₂5/6]O₂ and Li_0.7[Li_1/12Ni_1/12 Mn_5/6]O_1.9S_0.1, Li_0.7[Li_1/12Ni_1/12Mn_5/6]O_1.8S_0.2, and Li_0.7[Li_1/12Ni_1/12Mn_5/6]O_1.7S_0.3 delivered the discharge capacities of 238, 230,224, and 226 mAh/g, respectively, with their capacity fading rates of 0.34, 0.21, 0.12, 0.25%/cycle, respectively. The partial substitutions of Ni and S for Mn and O in Li_0.7[Li_1/12Ni_1/12Mn_1/12]O₂ significantly enhanced the electrochemical properties of the lithium manganese oxide materials.     

The effects of Ni and Li doping on the performance of lithium manganese oxide material for lithium secondary batteries

Layered Li_0.7[M_1/6Mn_5/6]O₂ (M=Li, Ni) was synthesized using a sol-gel method. P2-Na_0.7[M_1/6Mn_5/6]O₂ precursor was first synthesized by a sol-gel method, and then O2-Li_0.7[M_1/6Mn_5/6]O₂ was prepared by an ion exchange of Li for Na in P2-Na_0.7[M_1/6Mn_5/6]O₂ precursor. From charge/discharge curves, it was seen that Li_0.7[Li_1/6Mn_5/6]O₂ has two plateaus similar to those observed from a spinel structure, but Li_0.7[Ni_1/6Mn_5/6]O₂ holds a single plateau as observed from a typical layered structure. It was considered that Li_0.7[Li_1/6Mn_5/6]O₂ undergoes a phase transformation from layered to spinel structure during the charge/discharge cycle, but Li_0.7[Ni_1/6Mn_5/6]O₂ maintains O2-layered structure after the cycles. Li_0.7[Ni_1/6Mn_5/6]O₂ was higher in discharge capacity and retention rate than Li_0.7[Li_1/6Mn_5/6]O₂.     

掺杂氧化物对Ni/CeO2催化剂的催化性能的影响

在Ni/CeO2中掺杂Fe2O3、La2O3和MnO2,并用XRD、TPR、TPD等对掺杂的催化剂的晶相结构、表面性能等进行了表征。结果表明,掺杂Fe2O3有利于比表面积增大、CeO2粒度减小和晶格氧的形成,增强催化剂的乙醇吸附能力和氧化能力,提高催化剂的活性与抗积碳性。Ni/Fe2O3-CeO2催化剂在500℃时,乙醇转化率高达82.4%,氢气选择性69.3%。     

Effects of rare-earth oxide doping on the thermal radiation performance of HfO2 coating

In this study, the REO-HfO₂ (REO = Tb₄O₇, Gd₂O₃ and Sm₂O₃) coatings and pure HfO₂ coatings were prepared by atmospheric plasma spraying. The chemical compositions, morphologies, infrared radiation performance and thermal resistances of the coatings were systematically investigated. The experimental results showed that the Tb₄O₇-HfO₂, Gd₂O₃-HfO₂, Sm₂O₃-HfO₂ and pure HfO₂ coatings had infrared emissivity values of 0.863, 0.852, 0.854 and 0.621, respectively, at room temperature. Based on the phase analysis, the higher infrared emissivity of the REO-HfO₂ coatings could be attributed to the fact that the newly formed RE₂Hf₂O₇ (RE = Tb, Gd and Sm) phase, which had a defective fluorite-type structure, and the RE³⁺ ions enhanced the lattice absorption and electron absorption. Additionally, the Tb₄O₇-HfO₂ coating exhibited a relatively higher infrared emissivity than those of the Gd₂O₃-HfO₂ and Sm₂O₃-HfO₂ coating over the wavelength range of 1–15 μm, which was due to the relatively higher vibrational frequency of the TbO bond in RE₂Hf₂O₇ (RE = Tb, Gd and Sm) and the transformation of Tb³⁺ into Tb⁴⁺ in the Tb₄O₇-HfO₂ system. In addition, the REO-HfO₂ ceramic coatings exhibited excellent thermal resistance, which could withstand high-temperature treatment at 1600 °C for at least 50 h without undergoing a phase change and exfoliation, and the infrared emissivity at different temperatures hardly changed after thermal treatment.     

A novel microwave absorption material of Ni doped cryptomelane type manganese oxides

Cryptomelane type manganese oxide α-MnO₂ and Ni doped KMn₈O₁₆ nanostructures were synthesized by water-bathing methods at 80 °C for 24 h using NiSO₄·H₂O as the dopant sources. The structures, morphologies and physical properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results show that the products are Ni doped KMn₈O₁₆ nanorods after the introduction of NiSO₄·H₂O during the reaction process. The electromagnetic characteristics and microwave absorption properties of the materials were carried out with a vector network analyzer (VNA) and the transmission line (TML) theory. The dielectric loss and microwave absorption properties of the cryptomelane materials are improved after Ni doping. The thickness dependent reflection loss shows that the peak frequency and effective absorption bandwidth all decrease with the increasing material thickness. With the increase of Ni doping concentration, the peak frequency shifts to higher frequency bands and the effective absorption bandwidth increases. The electromagnetic performance of cryptomelane can be attributed to its unique tunnel structures and the improvement of Ni doping can be due to the enhanced electromagnetic polarization.     

Mn~(2+)掺杂及碳包覆对磷酸亚铁锂的影响

以醋酸锰为Mn源,葡萄糖为C源,采用高温固相法合成磷酸亚铁锂,对磷酸亚铁锂进行了Fe位掺杂和表面的包覆碳研究。用XRD、恒流充放电研究了材料的结构和电化学性能。结果表明:掺杂及包覆后的材料仍然具有橄榄石型晶体结构,并且掺杂及包覆碳后材料的初始容量和循环性能都得到了改善,表现出了良好的循环性能和高倍率性能。     

Influence of Ti and Fe doping on the structural and electrochemical performance of LiCo0.6Ni0.4O2 cathode materials for Li-ion batteries

The combination of lithium cobalt oxide (LCO) and lithium nickel oxide (LNO) property for Li-ion batteries (LIB) brings a very promising cathode material, LiCo_1?xNi_xO₂ with a high specific reversible capacity and good cycling behaviour. Nonetheless, high toxic Co content and an instability of Li⁺/Ni²⁺ interaction in LiCo_1?xNi_xO₂ crystal structure paved the way for some modification for the development of this potential material. In this research, the self-propagating combustion method is used to reduce 40% Co content of LCO by replacing it with 40% Ni content resulting in cathode material with the stoichiometry of LiCo_0.6Ni_0.4O₂ (LCN). To improve the stability of the LiCo_0.6Ni_0.4O₂ structure, 5% of Ti and Fe was substituted at the Co site of the LCN material. The effect of these different cation substitutions (Ti⁴⁺ and Fe³⁺) on the structural and electrochemical performance of layered LiCo_0.6Ni_0.4O₂ cathode materials was investigated. Rietveld refinement revealed that Fe doped material has the longest atomic distance Li–O in the structure that allow better Li⁺ diffusion during intercalation/deintercalation to give an excellent electrochemical performance (138 mAhg^?1). After 50th cycle, it is found that the discharge cycling for Ti and Fe substituted materials were improved by more than 5% compared to pristine material. Both Ti and Fe doped materials were also having less than 13% of capacity fading indicates that the substitution of some Co with Ti and Fe are stable and can retain their electrochemical properties.     

Effect of ZnO and TiO2 doping on the sintering behavior of Y2O3 ceramics

Full densification of Y₂O₃ is challenging and requires a very high sintering temperature (above 1700 °C). In this study, the effect of ZnO and TiO₂ dopants on its densification was investigated, showing that both dopants lowered the sintering temperature and improved the process. Moreover, ZnO promoted the grain growth, while TiO₂ inhibited it; hence, the ZnOTiO₂ co-doping and the change in the ZnO/TiO₂ ratio allowed the control of the sintered body microstructure while maintaining high densification. Since Y₂O₃ has a higher plasma erosion resistance than conventional Si-based materials, the plasma dry etching resistance of the sintered Y₂O₃ was also evaluated and found superior due to the improved densification and controlled grain size of the doped samples.     

Effect of calcination temperature on optical,magnetic and dielectric properties of Sol-Gel synthesized Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0–0.8)

The Ni_0.2Mg_0.8-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6 & 0.8) nanomaterials were prepared via sol-gel technique. These samples were calcined at three different temperatures (T) such as 400, 450 and 500 °C/5 h. Furthermore, the X-ray diffraction (XRD) patterns of all the calcined samples revealed the single phase cubic spinel structure. The lattice constants (a = b = c) were noticed to be increasing with increase of ‘x’. The grain shape, size and distribution of x = 0.0–0.8 contents were analyzed using field emission electron microscope (FESEM). The x = 0.2 content provided higher optical band gap energy (E_g) value than the remaining contents. Furthermore, the magnetization versus magnetic field (M − H) curves indicated the superparamagnetic nature of x = 0.0–0.8 contents. The high saturation magnetization (M_s) was noticed for x = 0.4 and 0.6 contents. In addition, the distribution of cations like Ni⁺², Mg⁺², Zn⁺², Fe⁺³ and Fe⁺² was performed between the tetrahedral (A) and octahedral (B) sites. The frequency dependence of dielectric constant (ε′), dielectric loss (ε") and ac-electrical conductivity (σ_ac) was investigated as a function of composition. Moreover, the temperature variation of ε′ showed the decreasing trend of dielectric transition temperature (T_e) with increase of ‘x’. The high ε′ of 163.1 (at 1 MHz) was noticed at x = 0.2 content calcined at 500 °C. Using the power law fit applied to the log σ_ac-log ω plots, the dc-electrical conductivity (σ_dc) and exponent (n) parameters were calculated.     

One-pot hydrothermal synthesis of Mn3O4 nanorods grown on Ni foam for high performance supercapacitor applications

Mn₃O₄/Ni foam composites were synthesized by a one-step hydrothermal method in an aqueous solution containing only Mn(NO₃)₂ and C₆H₁₂N₄. It was found that Mn₃O₄ nanorods with lengths of 2 to 3 μm and diameters of 100 nm distributed on Ni foam homogeneously. Detailed reaction time-dependent morphological and component evolution was studied to understand the growth process of Mn₃O₄ nanorods. As cathode material for supercapacitors, Mn₃O₄ nanorods/composite exhibited superior supercapacitor performances with high specific capacitance (263 F · g^-1 at 1A · g^-1), which was more than 10 times higher than that of the Mn₃O₄/Ni plate. The enhanced supercapacitor performance was due to the porous architecture of the Ni foam which provides fast ion and electron transfer, large reaction surface area, and good conductivity.     

Significant enhancement of catalytic activities of manganese oxide octahedral molecular sieve by marginal amount of doping vanadium

Vanadium doped hollandite-type manganese oxide octahedral molecular sieve (OMS-2) was synthesized by a simple hydrothermal route. The results of catalytic tests showed that marginal amount of doping vanadium had greatly enhanced catalytic activities of OMS-2 not only in low-temperature complete oxidation of formaldehyde at 140 °C but also in high-temperature complete oxidation of methane at 450 °C. The results of XPS, HRTEM and H₂-TPR measurements revealed that the enhancements of the catalytic activities primarily resulted from the increase of surface defect sites regardless of reaction temperatures and nature of reactants, rather than reducibility and average oxidation state of manganese.     

Enhanced Na-storage properties of O3-type NaNi0.5Mn0.5O2 cathodes by doping and coating dual-modification strategy

Due to their high theoretical specific capacities and good structural compatibility, O3-layered oxides are considered as high-performance cathode candidates for sodium-ion batteries. However, serious side reactions and structural degradation during long-term cycling have greatly hindered their practical applications. Herein, O3-type NaNi_0.5Mn_0.5O₂ (NNMO) was prepared by partially substituting Ni²⁺ with Cu²⁺ and inducing CuO surface coating to enhance the structural stability without sacrificing the high capacity. In Particular, Cu²⁺ incorporated at a molar ratio of 0.10 greatly improved the electrochemical performance of pristine NNMO. The NaMn_0.5Ni_0.4Cu_0.1O₂ electrode exhibited a capacity retention of 64.5% after 300 cycles at 0.5 C. Microscopic and spectral studies revealed that the CuO coating layer suppressed detrimental side reactions upon cycling. Moreover, the bulk doping of Cu²⁺ ultimately enhanced the structural stability by mitigating irreversible phase transitions. Hence, the integration of bulk Cu²⁺ doping and CuO surface coating contributed to the increased structural stability and electrochemical performance of NNMO. The doping and coating dual-modification strategy established in this work effectively suppressed the side reactions and structural degradation of NNMO, and this work provides new insight into the effective design of electrode microstructures for use in high-performance batteries.     

磁场对Ni/Al2O3催化剂结构及加氢性能的影响

采用共沉淀法制备了Ni/Al₂O₃加氢催化剂,在制备过程中引入交流电磁场对催化剂做强化制备,通过BET、SEM、XRD和TPR等方法对催化剂做表征,并将该催化剂应用于脂肪酸加氢反应中,考察了磁场强度对催化剂结构及加氢性能的影响。结果表明,制备过程中引入电磁场能够有效降低催化剂颗粒的团聚,增大催化剂的比表面积和平均孔径,提高催化剂的脂肪酸加氢活性。随着磁场强度的增强催化剂还原温度逐渐升高,结构稳定性增强,有效延长了催化剂的使用寿命。     

Effects of yttrium additions on the microstructure and charge transport properties of indium tin oxide semiconductors

The effects of yttrium (Y) additions (x=0, 0.05, 0.1, and 0.2) on the microstructure, chemical structure, and electrical properties of Y_xInSnO_y (YITO) thin films, prepared using a sol-gel process were examined. The transmission electron microscopy (TEM) observations showed that the undoped InSnO (ITO) film consisted of an amorphous structure with local crystalline domains on the film surface, whereas the Y additions (x=0.05, 0.1, and 0.2) to ITO suppressed the formation of the crystalline phase. X-ray photoelectron spectroscopy (XPS) analysis showed that the Y content decreased the concentration of oxygen vacancies owing to the strong incorporation of Y with oxygen. As a result of the Y incorporation, the carrier concentration of ITO films decreased. The saturation mobility (μ_sat), the on-off ratios (I_on/off), and the sub-threshold swing (S.S) of YITO films were 1.1 cm² V⁻¹ s⁻¹, ~10⁶, and ~0.5 V decade⁻¹, respectively, which are comparable with 1.7 cm² V⁻¹ s⁻¹, ~10⁵, and ~1.17 V decade⁻¹ of ITO film. Additionally, the initial threshold voltage (V_TH) was positive shift with increased of Y addition and V_TH shift (ΔV_TH) under the positive bias stress (PBS) results decreased by Y addition.     

Improved electrochemical performance of Li1.2Ni0.2Mn0.6O2 cathode material for lithium ion batteries synthesized by the polyvinyl alcohol assisted sol-gel method

Li-rich Mn-based cathode materials (Li_1.2Ni_0.2Mn_0.6O₂) have been synthesized by a polyvinyl alcohol (PVA)-assisted sol-gel method. The influence of PVA content on the structure and electrochemical performance of Li_1.2Ni_0.2Mn_0.6O₂ has been investigated respectively. XRD results of the Li_1.2Ni_0.2Mn_0.6O₂ powders show that they exhibit similar XRD patterns as those of Li-rich Mn-based cathode materials, and the crystalline nature of the layered compound are improved by the presence of PVA. Physical characterizations indicate that the as-synthesized oxide is composed of uniform and separated particles compared to the larged aggregated ones of the product synthesized under the same condition but without PVA. As cathode for lithium ion battery, the material synthesized with 10% PVA exhibits not only a relatively high discharge capacity of 254.2 mA h g⁻¹, but also excellent rate performance and good cycling performance. EIS results show that the material synthesized with PVA decreases the charge-transfer resistance and enhances the reaction kinetics, which is considered to be the major factor for higher rate performance.     

Enhancing the performance and stability of NiCo2O4 nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo₂O₄ electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo₂O₄/Ni@NF) shows the superior specific capacity of 1142 C g⁻¹ at 1 A g⁻¹ with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g⁻¹. These values are about 3.7 times higher than that of the electrode (NiCo₂O₄@NF) without a seed layer, which shows the specific capacity of 305 C g⁻¹@1 A g⁻¹ with cycle stability of 84% even at a lower current density of 1 A g⁻¹. The enhanced performance of the NiCo₂O₄/Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo₂O₄/Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe₂O₃ nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo₂O₄/Ni20@NF//rGO-Fe₂O₃@NF asymmetric solid state device delivers an areal capacitance of 446 mF cm⁻² with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm⁻² (at 3.58 kW cm⁻²) and power density of 14.88 kW cm⁻² (at 31.41 Wh cm⁻²).     

钴掺杂对Li1.2Mn0.6Ni0.2O2电化学性能的影响

利用共沉淀法制备了锂离子电池正极材料Li1.2Mn0.6Ni0.2O2和Li1.2Mn0.588Ni0.196Co0.016O2,并利用XRD、SEM和充放电测试对其晶体结构、形貌和电化学性能进行了表征.XRD结果表明:掺杂钴材料后,材料的层状结构保持完整,阳离子混排程度降低.电化学性能测试结果表明:掺钴材料的首次充放电效率和倍率放电性能明显优于Li1.2Mn0.6Ni0.2O2,且表现出较优的循环性能,其1、2、5C放电比容量分别为230.3、215.6、155.6 mA·h/g,1 C下循环50次的容量保持率为90.9％.     

镍/三氧化二铝油脂加氢催化剂研究

以铝酸钠和硫酸铝为原料制备铝胶,然后将可溶性镍盐、稀土硝酸盐与碱性沉淀剂中和后,加入到上述铝胶中,经水洗、干燥、还原即制得油脂加氢催化剂。氧化铝载体比表面积为(300±10)m2/g时,催化剂活性最高;综合考虑温度对氧化铝载体比表面积及催化剂过滤性能的影响,选取85℃为最佳温度;还原气中氮气、氢气体积比为3∶1时,得到的催化剂活性最好。该催化剂的活性评价结果表明,其性能已达到进口产品的水平。     

Liquid flame spray fabrication of WO3-reduced graphene oxide nanocomposites for enhanced O3-sensing performances

WO₃ is one of the inspiring sensing materials that show high response to O₃; an efficient fabrication of WO₃ film with incorporation of complementary additives is essential for enhanced sensitivity. Here we report film deposition by liquid flame spraying, characterization of nanostructured WO₃-reduced graphene oxide (rGO) composites and their gas-sensing activities to O₃. The starting feedstock was prepared from WC_l6 and rGO for pyrolysis synthesis by flame spraying. Nano-porous WO₃-rGO films were successfully fabricated and characterized by transmission electron microscopy, field emission scanning electron microscopy, Raman spectrometry, thermal analyses and X-ray diffraction. Nanosized WO₃ grains exhibited oriented nucleation on rGO flakes whereas rGO retained intact its nano-structural features after spraying. Constrained grain growth of WO₃ of 60–70 nm in size was realized in the rGO-containing films with as compared to ~220 nm in the pure WO₃ film. The WO₃-rGO film sensors showed quicker response to O₃ and faster recovery than rGO-free WO₃ film sensors. Addition of rGO in 1.0 wt% or 3.0 wt% in the films caused a significantly reduced effective working temperature of the film sensors from ~ 250 °C to ~ 150 °C.     

Effect of heat treatment on the structure and photocatalytic properties of BiYO3 and BiY0.995Ni0.005O3 ceramic powders

BiYO₃ powders were synthesized by the Pechini method under low-temperature conditions. When the heat treatment was performed at T < 600 °C, a mixture of tetragonal and cubic phases was obtained, while for T ≥ 600 °C, only the fluorite-like cubic phase was observed. Based on the Rietveld refinement, approximately 2% and 1% of the tetragonal phase remained in samples calcined at 400 °C and 500 °C for 1 h, respectively. The crystal size calculated for these samples was 4.4–48.1 nm, depending on the calcination temperature. The specific surface area of the samples diminished with heat treatment and reached a minimum at 800 °C. The band gap of samples with mixed phases was close to 2.16 eV and was ~2 eV for samples with a cubic phase. Photocatalytic tests demonstrate that BiY_0.995Ni_0.005O₃ calcined at 800 °C had the best performance: it degraded more than 80% of the antibiotic oxytetracycline when irradiated with visible light. The Ni-doped BiYO₃ material could degrade the antibiotic in tap water at an environmentally relevant concentration (μg L⁻¹ levels) and showed steady activity throughout four reaction cycles.