共查询到20条相似文献,搜索用时 20 毫秒
1.
The melt-spinning technique is applied to the preparation of the nanocrystalline and amorphous Mg2Ni-type alloys with nominal compositions of Mg2Ni1−xMnx (x = 0, 0.1, 0.2, 0.3, 0.4). The as-spun alloy ribbons possessing a continuous length, a thickness of about 30 μm and a width of about 25 mm were prepared. The structures of the as-spun alloy ribbons are characterized by XRD and TEM. The electrochemical performances of the as-spun alloy ribbons are measured by an automatic galvanostatic system. The results show that no amorphous structure is detected in the as-spun Mg2Ni alloy, whereas the as-spun Mg2Ni0.6Mn0.4 alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni notably intensifies the amorphous forming ability of the Mg2Ni-type alloy. The amorphization degree of the as-spun alloys containing Mn increases with increasing spinning rate. The melt spinning also significantly enhances the electrochemical performances such as the discharge capacity and the electrochemical cycle stability of the Mn-containing alloys. Furthermore, the high rate dischargeability (HRD) of the (x ≤ 0.1) alloys increases with an increase in the spinning rate, while for the (x ≥ 0.2) alloys, the HRD exhibits a maximum value at a particular spinning rate, and it varies with the change in Mn contents of the alloys. 相似文献
2.
To improve the cathodic performance of olivine-type LiMnPO4, we investigated the optimal annealing conditions for a composite of carbon with cation doping. Nanocrystalline and the cation-doped LiMn1−xMxPO4 (M = Ti, Mg, Zr and x = 0, 0.01, 0.05 and 0.10) was synthesized in aqueous solution using a planetary ball mill. The synthesis was performed at the fairly low temperature of 350 °C to limit particle size. The obtained samples except for the Zr doped one consisted of uniform and nano-sized particles. The performance of LiMnPO4 was much improved by an annealing treatment between 500 and 550 °C with carbon in an inert atmosphere. A small amount of metal-rich phosphide (Mn2P) was detected in the sample annealed at 900 °C. In addition, 1 at.% Mg doping for Fe enhanced the rate capability in our doped samples. The discharge capacity of LiMn0.99Mg0.01PO4/C was 146 mAh/g at 0.1 mA/cm2 and 125 mAh/g even at 2.0 mA/cm2. 相似文献
3.
Oxygen reduction reaction (ORR) on Pt microelectrode was used for developing a micro pH sensor for scanning electrochemical microscopy (SECM) study in this work. When the potential of Pt microelectrode was held constant in ORR region, the ORR current (cathodic current) increased with decreasing solution pH and vice versa. The response time of the ORR current to pH changes was measured to be ca. 30 ms which implies that the pH response is fast enough for monitoring the temporal pH changes. Furthermore, a fine linear relationship was found to exist between the half wave potential of ORR (E1/2) and the solution pH value, and the slope is −46 mV/pH. The Pt micro pH sensor was located 1 μm above the LaNi5−xAlx (x = 0, 0.3) substrate electrode surface in pH = 9 KOH solution to perform the tip-substrate voltammetry of SECM. In tip voltammogram, the ORR tip current qualitatively reflects the transit solution pH changes during LaNi5−xAlx discharge reaction. Also, the minimum values of the solution pH near LaNi5 and LaNi4.7Al0.3 surface during the discharge reaction were quantitatively detected; they were 7.17 and 7.57, respectively. The result indicates that Al partial substitution for Ni degrades the maximum discharge ability of the alloy and decreases the hydrogen diffusion coefficient in alloy bulk. 相似文献
4.
Ibro Tabakovic Venkateswara Inturi Jeremy Thurn Mark Kief 《Electrochimica acta》2010,55(22):6749-6754
Electrodeposition of Ni1−xFex (x = 0.1-0.9) films was carried out from a chloride plating solution containing saccharin as an organic additive at a constant current density (5 mA/cm2) and a controlled pH of 2.5. X-ray diffraction studies revealed the existence of an fcc, or γ phase, in the range of 10-58 wt.% Fe, a mixed fcc/bcc phase in the range of 59-60 wt.% Fe, and a bcc, or α phase in the range of 64-90 wt.% Fe. The saturation magnetization, Bs, of electrodeposited Ni1−xFex alloys at the room temperature was found to increase with the increase of Fe-content and follows the Slater-Pauling curve, but deviates from as-cast bulk NiFe alloys. The coefficient of thermal expansion, CTE, of electrodeposited alloys at room temperature also deviates from as-cast bulk NiFe alloys. Annealing of α-Ni36Fe64 alloy results in a martensitic α → γ phase transformation, which takes place between 300 and 400 °C. It was demonstrated that thermal treatment above 400 °C was necessary to obtain magnetic and mechanical properties similar to those to conventional Invar alloy. Annealing of α-Ni36Fe64 alloy at 700 °C brings about a decrease of Bs from 1.75 to 0.45 T. By controlling the annealing conditions of α → γ martensitic transformation, it is possible to adjust the CTE of Ni36Fe64 alloy over the broad limits from 2.7 to 8.7 × 10−6/°C. 相似文献
5.
Layered Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) have been prepared by the mixed hydroxide and molten-salt synthesis method. The individual particles of synthesized materials have a sub-microsize range of 200-500 nm, and LiNi0.475Mn0.475Zr0.05O2 has a rougher surface than that of LiNi0.5Mn0.5O2. The Li/Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) electrodes were cycled between 4.5 and 2.0 V at a current density of 15 mA/g, the discharge capacity of both cells increased during the first ten cycles. The discharge capacity of the Li/LiNi0.475Mn0.475Zr0.05O2 cell increased from 150 to 220 mAh/g, which is 50 mAh/g larger than that of the Li/LiNi0.5Mn0.5O2 cell. We found that the oxidation of oxygen and the Mn3+ ion concerned this phenomenon from the cyclic voltammetry (CV). Thermal stability of the charged Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) cathode was improved by Zr doping. 相似文献
6.
Evolution of the local structure and electrochemical properties of spinel LiNixMn2−xO4 (0 ≤ x ≤ 0.5)
A series of Ni substituted spinel LiNixMn2−xO4 (0 ≤ x ≤ 0.5) have been synthesized to study the evolution of the local structure and their electrochemical properties. X-ray diffraction showed a few Ni cations moved to the 8a sites in heavily substituted LiNixMn2−xO4 (x ≥ 0.3). X-ray photoelectron spectroscopy confirmed Ni2+ cations were partially oxidized to Ni3+. The local structures of LiNixMn2−xO4 were studied by analyzing the and A1g Raman bands. The most compact [Mn(Ni)O6] octahedron with the highest bond energy of Mn(Ni)O was found for LiNi0.2Mn1.8O4, which showed a Mn(Ni)O average bond length of 1.790 Å, and a force constant of 2.966 N cm−1. Electrolyte decomposition during the electrochemical charging processes increased with Ni substitution. The discharge capacities at the 4.1 and 4.7 V plateaus obeyed the linear relationships with respect to the Ni substitution with the slopes of −1.9 and +1.9, which were smaller than the theoretical values of −2 and +2, respectively. The smaller slopes could be attributed to the electrochemical hysteresis and the presence of Ni3+ in the materials. 相似文献
7.
The La2−xAxMo2O9−δ (A = Ca2+, Sr2+, Ba2+ and K+) series has been synthesised as nanocrystalline materials via a modification of the freeze-drying method. The resulting materials have been characterised by X-ray diffraction (XRD), thermal analysis (TG/DTA, DSC), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The high-temperature β-polymorph is stabilised for dopant content x > 0.01. The nanocrystalline powders were used to obtain dense ceramic materials with optimised microstructure and relative density >95%. The overall conductivity determined by impedance spectroscopy depends on both the ionic radius and dopant content. The conductivity decreases slightly as the dopant content increases in addition a maximum conductivity value was found for Sr2+ substitution, which show an ionic radii slightly higher than La3+ (e.g. 0.08 S cm−1 for La2Mo2O9 and 0.06 S cm−1 for La1.9Sr0.1Mo2O9−δ at 973 K). The creation of extrinsic vacancies upon substitution results in a wider stability range under reducing conditions and prevents amorphisation, although the stability is not enhanced significantly when compared to samples with higher tungsten content. These materials present high thermal expansion coefficients in the range of (13-16) × 10−6 K−1 between room temperature and 753 K and (18-20) × 10−6 K−1 above 823 K. The ionic transport numbers determined by a modified emf method remain above 0.98 under an oxygen partial pressure gradient of O2/air and decreases substantially under wet 5% H2-Ar/air when approaching to the degradation temperature above 973 K due to an increase of the electronic contribution to the overall conductivity. 相似文献
8.
Mg-Ni-Ti-based hydrogen storage alloys Mg0.9Ti0.1Ni1−xMx (M = Co, Mn; x = 0, 0.1, 0.2) were prepared by means of mechanical alloying (MA). The effects of partial substitution of Ni with Co or Mn on the microstructures and electrochemical performance of the alloys were investigated. The result of X-ray diffraction (XRD) shows that the alloys exhibit dominatingly amorphous structures. The electrochemical measurements indicate that the substitution of Ni can dramatically enhance the cycle stability of Mg-Ni-Ti-based alloys. After 50 charge/discharge cycles, the capacity retention rate of the alloy electrodes increases from 30% (Mg0.9Ti0.1Ni) to 59% (Mg0.9Ti0.1Ni0.9Co0.1), 58% (Mg0.9Ti0.1Ni0.9Mn0.1), 46% (Mg0.9Ti0.1Ni0.8Co0.2) and 53% (Mg0.9Ti0.1Ni0.8Mn0.2), respectively. Among these alloys, the Mg0.9Ti0.1Ni0.9Mn0.1 alloy presents better overall electrochemical performance. The cyclic voltammograms (CV) and anti-corruption test reveal that the electrochemical cycle stability of these alloys is improved by substituting Ni with Co or Mn. 相似文献
9.
Gang Deng Mingda Tao Chaoling Wu Xiangqian Shen Heng Yang 《Electrochimica acta》2009,54(15):3910-3914
La(1−x)SrxFeO3 (x = 0.2,0.4) powders were prepared by a stearic acid combustion method, and their phase structure and electrochemical properties were investigated systematically. X-ray diffraction (XRD) analysis shows that La(1−x)SrxFeO3 perovskite-type oxides consist of single-phase orthorhombic structure (x = 0.2) and rhombohedral one (x = 0.4), respectively. The electrochemical test shows that the reaction at La(1−x)SrxFeO3 oxide electrodes are reversible. The discharge capacities of La(1−x)SrxFeO3 oxide electrodes increase as the temperature rises. With the increase of the temperature from 298 K to 333 K, their initial discharge capacity mounts up from 324.4 mA h g−1 to 543.0 mA h g−1 (when x = 0.2) and from 147.0 mA h g−1 to 501.5 mA h g−1 (when x = 0.4) at the current density of 31.25 mA g−1, respectively. After 20 charge-discharge cycles, they still remain perovskite-type structure. Being similar to the relationship between the discharge capacity and the temperature, the electrochemical kinetic analysis indicates that the exchange current density and proton diffusion coefficient of La(1−x)SrxFeO3 oxide electrodes increase with the increase of the temperature. Compared with La0.8Sr0.2FeO3, La0.6Sr0.4FeO3 electrode is a more promising candidate for electrochemical hydrogen storage because of its higher cycle capacity at various temperatures. 相似文献
10.
Composite G/PPy/PPy(La1−xSrxMnO3)/PPy electrodes made of the perovskite La1−xSrxMnO3 embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La1−xSrxMnO3) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm−3 pyrrole (Py) plus 0.05 mol dm−3 K2SO4 with and without containing a suspension of 8.33 g L−1 oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm−3 K2SO4 plus 5 mmol dm−3 KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR. 相似文献
11.
A series of ZnxMg1 − xGa2O4:Co2+ spinels (x = 0, 0.25, 0.5, 0.75, and 1.0) was successfully produced through low-temperature burning method by using Mg(NO3)2·4H2O, Zn(NO3)2·6H2O, Ga(NO3)3·6H2O, CO(NH2)2, NH4NO3, and Co(NO3)2·6H2O as raw materials. The product was characterized by X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The product was not merely a simple mixture of MgGa2O4 and ZnGa2O4; rather, it formed a solid solution. The lattice constant of ZnxMg1 − xGa2O4:Co2+ (0 ≤ x ≤ 1.0) crystals has a good linear relationship with the doping density, x. The synthesized products have high crystallinities with neat arrays. Based on an analysis of the form and position of the emission spectrum, the strong emission peak around the visible region (670 nm) can be attributed to the energy level transition [4T1(4P) → 4A2(4F)] of Co2+ in the tetrahedron. The weak emission peak in the near-infrared region can be attributed to the energy level transition [4T1(4P) → 4T2(4F)] of Co2+ in the tetrahedron. 相似文献
12.
Layered Li1+x(Ni0.3Co0.4Mn0.3)O2−δ (x = 0, 0.03 and 0.06) materials were synthesized through the different calcination times using the spray-dried precursor with the molar ratio of Li/Me = 1.25 (Me = transition metals). The physical and electrochemical properties of the lithium excess and the stoichiometric materials were examined using XRD, AAS, BET and galvanostatic electrochemical method. As results, the lithium excess Li1.06(Ni0.3Co0.4Mn0.3)O2−δ could show better electrochemical properties, such as discharge capacity, capacity retention and C rate ability, than those of the stoichiometric Li1.00(Ni0.3Co0.4Mn0.3)O2−δ. In this paper, the effect of excess lithium on the electrochemical properties of Li1+x(Ni0.3Co0.4Mn0.3)O2−δ materials will be discussed based on the experimental results of ex situ X-ray diffraction, transmission electron microscopy (TEM) and galvanostatic intermittent titration technique (GITT) 相似文献
13.
14.
Sub-micron Bi2Ru2O7+x + RuO2 oxide sensing electrodes (SE) for water quality sensors were prepared on platinised ceramic substrate of the sensor. Their morphology was analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Sensing properties of the Bi2Ru2O7+x + RuO2-SE were investigated for potentiometric detection of pH and dissolved oxygen (DO) in water in the temperature range of 4–30 °C. Sensor was capable to measure DO from 0.5 to 8.0 ppm and pH from 2.0 to 13.0, respectively. The obtained results show acceptable linearity of the measuring characteristics. Long-term stability trial for Bi2Ru2O7+x + RuO2-SE revealed that bio-fouling can be one of the main destructive factors affecting the performance of the sensors in the long run. The screen-printing technology used in the multi-sensory implementation provides fundamental properties of miniaturization, reasonable accuracy and low cost. 相似文献
15.
A novel SOM process was used to prepare CeNi5 and LaxCe1−xNi5 hydrogen storage alloys directly from their mixed oxides. The electrolytic reduction was carried out in molten CaCl2 system at 1000 °C. The reduction mechanism was investigated by analyzing the chemical compositions and the phase constitutions of the intermediate products of electrolysis. The results suggested that the reduction of NiO-CeO2 may take place in two steps: first, NiO was reduced into Ni and CeO2 reacted with CaCl2 to form CeOCl, then Ni reacted with CeOCl leading to the formation of CeNi5. It was found that the reduction rate increased while decreasing the pressure load of the mixed oxide pellets. Furthermore, CeNi5 could not be produced if the pressure load was lower than 10 MPa. It was also found that the pellets of NiO-CeO2 could be completely reduced to CeNi5 alloy by the SOM process, which was greatly excelled than FFC process. The successful preparation of LaxCe1−xNi5 (x = 0-1) alloy reported here suggests that the SOM process may be promising for the industrial application of producing such alloys. 相似文献
16.
The structure and electrochemical properties of TiV1.1Mn0.9Nix (x = 0.1-0.7) solid solution electrode alloys have been investigated. It is found that these alloys mainly consist of a solid solution phase with body centered cubic (bcc) structure and a C14 Laves secondary phase. The solid solution alloys show easy activation behavior, high temperature dischargeability, high discharge capacity and favorable high-rate dischargeability as a negative electrode material in Ni-MH battery. The maximum discharge capacity is 502 mAh g−1 at 303 K when x = 0.4. Electrochemical impedance spectroscopy (EIS) test shows that the charge-transfer resistance at the surface of the alloy electrodes decreases obviously with increasing Ni content. 相似文献
17.
The effect of Mn content on the crystal structure and electrochemical characteristics of La0.7Mg0.3Ni2.975−xCo0.525Mnx (x = 0, 0.1, 0.2, 0.3, 0.4) alloys has been studied systematically. The results of the Rietveld analyses show that all these alloys mainly consist of two phases: the La(La,Mg)2Ni9 phase with the rhombohedral PuNi3-type structure and the LaNi5 phase with the hexagonal CaCu5-type structure. The pressure-composition isotherms shows that the partial substitution of Mn for Ni results in lower desorption plateau pressure and steeper pressure plateau of the alloy electrodes. For a Mn content of x = 0.3, the electrochemical performances, including specific discharge capacity, high rate chargeability (HRC) and high rate dischargeability (HRD), of the alloy are preferable. Moreover, the data of the polarization resistance Rp and the exchange current density I0 of the alloy electrodes is consistent with the results of HRC and HRD. The hydrogen diffusion coefficient D increases with increasing Mn content, and thereafter increases the low temperature dischargeability (LTD) of the alloy electrodes. 相似文献
18.
J. Jiang 《Electrochimica acta》2005,50(24):4778-4783
Samples of the layered cathode materials, Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (x = 1/12, 1/4, 5/12, and 1/2), were synthesized at 900 °C. Electrodes of these samples were charged in Li-ion coin cells to remove lithium. The charged electrode materials were rinsed to remove the electrolyte salt and then added, along with EC/DEC solvent or 1 M LiPF6 EC/DEC, to stainless steel accelerating rate calorimetry (ARC) sample holders that were then welded closed. The reactivity of the samples with electrolyte was probed at two states of charge. First, for samples charged to near 4.45 V and second, for samples charged to 4.8 V, corresponding to removal of all mobile lithium from the samples and also concomitant release of oxygen in a plateau near 4.5 V. Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 samples with x = 1/4, 5/12 and 1/2 charged to 4.45 V do not react appreciably till 190 °C in EC/DEC. Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 samples charged to 4.8 V versus Li, across the oxygen release plateau, start to significantly react with EC/DEC at about 130 °C. However, their high reactivity is similar to that of Li0.5CoO2 (4.2 V) with 1 μm particle size. Therefore, Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 samples showing specific capacity of up to 225 mAh/g may be acceptable for replacing LiCoO2 (145 mAh/g to 4.2 V) from a safety point of view, if their particle size is increased. 相似文献
19.
?brahim Y. Erdo?an 《Electrochimica acta》2010,55(22):6402-2393
This study reports on the synthesis of ternary semiconductor (BixSb1−x)2Te3 thin films on Au(1 1 1) using a practical electrochemical method, based on the simultaneous underpotential deposition (UPD) of Bi, Sb and Te from the same solution containing Bi3+, SbO+, and HTeO2+ at a constant potential. The thin films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-FTIR (RA-FTIR) to determine structural, morphological, compositional and optic properties. The ternary thin films of (BixSb1−x)2Te3 with various compositions (0.0 ≤ x ≤ 1.0) are highly crystalline and have a kinetically preferred orientation at (0 1 5) for hexagonal crystal structure. AFM images show uniform morphology with hexagonal-shaped crystals deposited over the entire gold substrate. The structure and composition analyses reveal that the thin films are pure phase with corresponding atomic ratios. The optical studies show that the band gap of (BixSb1−x)2Te3 thin films could be tuned from 0.17 eV to 0.29 eV as a function of composition. 相似文献
20.
LiNiO2, LiNi0.995Al0.005O2, LiNi0.975Ga0.025O2, LiNi0.990Ti0.010O2 and LiNi0.990Al0.005Ti0.005O2 specimens were synthesized by preheating at 400 °C for 30 min in air and calcination at 750 °C for 36 h in an O2 stream. The variation of the discharge capacities with C-rate for the synthesized samples was investigated. LiNi0.990Al0.005Ti0.005O2 has the largest first discharge capacities at the 0.1 and 0.2 C rates. LiNi0.990Ti0.010O2 has the largest first discharge capacity at the 0.5 C rate. In case of LiNiO2 and LiNi0.990Ti0.010O2, the first discharge capacity decreases slowly as the C-rate increases. LiNiO2 has the largest discharge capacities at n = 10 (after stabilization of the cycling performance) at the 0.1, 0.2 and 0.5 C rates. This is considered to be related with the largest value of I0 0 3/I1 0 4 and the smallest value of R-factor (the least degree of cation mixing) among all the samples. LiNi0.975Ga0.025O2 exhibits the lowest discharge capacity degradation rates at 0.1, 0.2 and 0.5 C rates. 相似文献