Ni Doping Amount Research Articles

Comparison of novel Ni doped exsolution perovskites as methane dry reforming catalysts

Three perovskite-type materials with a different amount of B-site Ni doping have been tested for their catalytic performance during me-thane dry reforming (MDR) followed by characterization with X-ray dif-fraction (XRD) and scanning electron microscopy (SEM). They could be activated via a reductive treatment (either during a pre-reduction step or di-rectly in reducing reaction atmosphere), the main activating mechanism be-ing the formation of Ni nanoparticles on the surface by exsolution. The catalytic activity increased with the particle size and density. The particle distribution properties could be improved by increasing the amount of Ni doping from 3 % to 10 %, by using an A-site sub-stoichiometric perovskite and by choosing a higher annealing temperature during material prepara-tion. A deactivation over time was observed, due to segregation of CaCO3 on the surface, but no coking or particle sintering occurred

Impedance analysis of charge transfer upon nickel doping in Tio2-based flexible dye-sensitized solar cell

Flexible dye-sensitized solar cells (FDSSCs) have promoted interest in plastic industries as they are lightweight, flexible, and mechanically robust to accelerate production and reduce cost. However, the plastic substrates have temperature limitations in producing the TiO2 photoanode and degrade the performance of FDSSC. The main reason for this degradation is the low charge transfer in the photoanode layer. Although there is plenty of research on low-temperature fabrication methods, they indirectly increase the operational cost. Therefore, a new approach is necessary for charge transfer improvement without affecting the temperature in a low-cost platform. In this study, we present a photoanode that improves the charge transfer by doping nickel (Ni) in the TiO2 layer. A low amount of Ni doping (15%) exhibited Rct >> Rt, indicating a high charge transport and low electron recombination rate (120.84 s−1). On the other hand, higher amount Ni doping (>> 45%) has Rct << Rt which deteriorates the performance of the cell by causing severe agglomeration issues, indicating a high electron recombination rate (369.75 s−1). Moreover, the high charge transfer in (TiO2)85-Ni15-based FDSSC facilitates the electron lifetime of the cell up to 8.28 ms. Therefore, an optimum doping of Ni in TiO2-based FDSSC is studied in this work.

Synthesis and Dispersion of Ni-Doped Cu&lt;sub&gt;2&lt;/sub&gt;ZnSnS&lt;sub&gt;4&lt;/sub&gt;

This paper reports the preliminary study on the synthesis of Ni doped CZTS (Cu2ZnSnS4:Ni) particle 5 at.% of Cu by solution method and dispersion of the obtained particles by beads mill method at various dispersing agents (SDS, CTAB, and Tween80). The phase transformation of the obtained particles was analyzed from the XRD spectra and XRF elemental analysis. The phase transformation and amount of Ni-doped to particles was predicted employing commercially available analytical software tool Match! Version 2.x. Moreover, the dispersion characteristics were investigated includes size, size distribution, and zeta potential of bare particles in comparison to various dispersing agents. This characteristic related to the future application of CZTS as an absorber in a thin-film based PV. The XRD analysis showed that the obtained particle contained crystal structure of copper sulfate pentahydrate (75.9 %), Ni(HN2S2)2 (12.5 %), and Cu2ZnSnS4 (11.6%). The XRF elemental analysis showed that amount of Ni-doped was 6.8 at.%; it was higher than the initial design amount of Ni doping. The dispersion of suspended particles was the majority (90%) with an average size of 3.06 µm and only 10 % with size 255 nm. Beads-milling of particles without dispersing agents did not disintegrate agglomerated particles. It is highlighted dispersion only using magnetic stirred with SDS dispersing agent provides the best suspension with a majority (60%) in 166 nm and only 30 % with average size 3.06 µm with relatively high zeta potential (-17 mV). It was concluded that the presence of a multi-phase crystal needs to be resolved either by proper calcination at a higher temperature than 400°C or further heating at a higher temperature during film preparation. High-energy centrifugation of zirconia beads mill caused desorption of adsorbed steric stabilization of dispersing agent under investigation. Further investigation on the coating process to facilitated laboratory fabrication of thin-film absorber with SDS as a dispersing agent is necessary to carry out concerning the properties of the thin-film.

Magnetic MoS2: a promising microwave absorption material with both dielectric loss and magnetic loss properties

In order to obtain magnetic MoS2 and investigate the influence of magnetic moment on the microwave absorption properties of MoS2, transition metal element Ni-doped MoS2 (0–30 at%) was obtained by a hydrothermal synthesis. The results revealed that the low doping concentration (<10 at%) did not significantly change the crystal structure of MoS2, and the Ni element formed a NixMo1−xS2 compound within the MoS2 bulk phase. While the high doping concentration (10–30 at%) led to the formation of impurities. The hydrothermal products which were formed by the accumulation of pleated nanosheets looked like spherical flowers. As the doping concentration further increased, the spherical particles became more compact. The magnetization of MoS2 could be increased by proper amount of Ni doping. When doping with 3 at% Ni (Ni-3), the Ms value increased from 0.53 emu g−1 for non-doped MoS2 to 0.93 emu g−1. When the doping ratio was further increased, the Ms value of the material decreased. The zigzag edges and variations in the number of vacancies in the materials may be the root of changes in magnetic properties. The overall performance of Ni-3 was also the best in the examined doping range. Compared with non-doped MoS2, the matching thickness decreased from 3.50 to 2.05 mm, while the minimum reflection loss value decreased from −55.18 to −58.08 dB, and the effective absorption bandwidth (<−10 dB) increased from 3.05 to 5.19 GHz. The excellent absorption performance of the doped materials can be attributed to the change of complex dielectric constant and complex permeability of MoS2 and resulting in the improvement of loss capability. This study may introduce new opportunities for fully exploiting these nanocrystals for microwave absorption, even for diluted magnetic semiconductors.

Low Ni-doped Co3O4 porous nanoplates for enhanced hydrogen and oxygen evolution reaction

In this paper, low Ni-doped Co3O4 (Ni: 2 wt%, 4 wt%, 6 wt% and 8 wt%) porous nanoplates are synthesized by hydrothermal method and annealing treatment. For the low Ni-doped Co3O4, X-ray diffraction (XRD) and Raman data show that the Ni ions are successfully incorporated into the Co3O4 lattices. Electrochemical measurements indicate that Co3O4 with low amount of Ni doping possesses remarkably enhanced activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. And especially, 4 wt% Ni-doped Co3O4 possesses the most efficient activity with an overpotential of 240 mV at the current density of 10 mA cm−2 for OER and 120 mV for HER in 1 M KOH than the pure Co3O4 and other Ni-doped Co3O4 samples. Our study suggests that the low doping would have a great potential in rational design of spinel oxides toward highly efficient electrocatalysis.

Cycle of Ni(II)-Ni(III)-Ni(II) in Ni-doped layered double hydroxides for activation of intercalated peroxydisulfate

Peroxydisulfate (PDS) activation has attracted much attention for the treatment of drinking water systems. In this work, Ni-doped MgAl layered double hydroxides (Ni-LDHs, Ni:Mg = 1:100 to 1:1, molar ratio) were prepared for the activation of PDS via intercalation. Compared with the case without Ni, doping with Ni resulted in much higher phenol degradation at the same PDS dosage. This was attributed to the activation of PDS, as the PDS consumption increased with increasing Ni doping amount. Moreover, radicals corresponding to organic decomposition were detected in the presence of Ni. Physical characterization results reveal that Ni(II) was converted to Ni(III) with PDS and then reduced back to Ni(II) during organic decomposition. To our best knowledge, this is the first study to report a cycle of Ni(II)-Ni(III)-Ni(II) in LDHs for the efficient activation of PDS. This effect was also observed in cases of odorous substances such as 4-bromophenol, 2-methylisoborneol, and geosmin. Our work provides a promising approach for the activation of PDS by Ni-LDHs.

Detrimental phase evolution triggered by Ni in perovskite-type cathodes for CO2 electroreduction

Abstract Perovskite oxides are popular as cathode materials of solid oxide electrolysis cells, because of their good redox stability and high resistance to coke formation. Unexpectedly, a negative effect of Ni doping is found on Sr2Fe1.5-xNixMo0.5O (x = 0, 0.05, 0.1, 0.2) cathode for pure CO2 electroreduction at 800 °C, although Ni is highly active for CO2 electroreduction. The CO2 electroreduction performance degrades with the increase of Ni doping amount. Various characterization techniques are used to disclose the negative effect. Ni doping decreases the perovskite stability under electroreduction conditions, Fe and Ni cations in the B-site are reduced to metal nanoparticles and SrCO3 forms on the surface of the perovskite. The phase instability results from the weaker Ni O bond. Although the Fe-Ni nanoparticles are in favor of the CO2 electroreduction, too much SrCO3 and carbon deposition block the charge transfer and diffusion of oxygenous species on the cathode surface.

Hydrothermal synthesis of Ni-doped ZnS solid solution photocatalysts for photocatalytic H2 production

When the Ni doping amount is 0.3, excessive Ni doping will result in NiS impurity levels (IL). NiS IL will increase the probability of recombination of photogenerated electron–hole pairs, which has negative influence on the photocatalytic H2 production. Moreover, Zn0.98Ni0.02S photocatalyst prepared at 180 °C for 12 h exhibits the best photocatalytic activity for photocatalytic hydrogen evolution reaction (PHER) with an initial rate of 457.11 μmol h−1 g−1, which is about 5 times higher than that over pure ZnS.

Preparation, Characterization and Surface Free Energy of Nickel-Doped Silica Organic-Inorganic Hybrid Membrane for H₂/CO₂ Separation.

Nickel-doped silica organic-inorganic hybrid (Ni/SiO₂) membranes based on tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) were prepared via a sol-gel process for H₂/CO₂ separation. The influence of calcination temperature and Ni-doping amount on the microstructure and surface free energy of Ni/SiO₂ materials was investigated. The permeance of H₂ and CO₂ and vapor stability of the membranes were tested. For the Ni/SiO₂ membrane, the optimal calcination temperature should be 350 °C and Ni/TEOS molar ratio is 0.1. After calcination at 350 °C, nickel element exists in form of Ni-O-Si structure and crystalline NiO with small grain size. At this temperature, the water contact angle of Ni/SiO₂ film achieved a maximum of (96.1±0.4)° and the surface free energy reached the minimum. The H₂ and CO₂ permeance of freshly-prepared the Ni/SiO₂ membrane was 7.86×10-6 and 1.50×10-6 mol m-2 Pa-1 s-1, respectively, at 25 °C and a pressure difference of 0.4 MPa. Compared with the pure SiO₂ membrane, the H₂ permeance and H₂/CO₂ selectivity of Ni/SiO₂ membrane increased by 20.9% and 15.9%, respectively. After aging in the moist condition for 7 d, the H₂ permeance of Ni/SiO₂ membrane was reduced by 6.9% and the H₂/CO₂ selectivity increased by 4.7%. The Ni/SiO₂ membrane showed higher H₂ permeance, H₂/CO₂ selectivity and vapor stability than pure SiO₂ membrane.

Influence of Ni doping on the structural, ferroelectric, magnetic and optical properties of $$\hbox {Bi}_{0.85}\hbox {Nd}_{0.15}\hbox {Fe}_{1-x}\hbox {Ni}_{x}\hbox {O}_{3}$$ thin films

\(\hbox {Bi}_{0.85}\hbox {Nd}_{0.15}\hbox {Fe}_{1-x}\hbox {Ni}_{x}\hbox {O}_{3}\) (\(x = 0.025\)–0.125) thin films were synthesized by applying a sol–gel method on fluorine-doped tin oxide substrates. The influence of Ni doping concentration on the structure, leakage current, ferroelectric, magnetic and optical properties of \(\hbox {Bi}_{0.85}\hbox {Nd}_{0.15}\hbox {Fe}_{1-x}\hbox {Ni}_{x}\hbox {O}_{3}\) thin films was investigated. \(\hbox {Bi}_{0.85}\hbox {Nd}_{0.15}\hbox {Fe}_{1-x}\hbox {Ni}_{x}\hbox {O}_{3}\) thin films are polycrystalline films that present a single perovskite structure without any impurity phase when the Ni doping concentration is below 0.1 and present a \(\hbox {Bi}_{2}\hbox {Fe}_{4}\hbox {O}_{9}\) phase when the Ni doping concentration is above 0.1. The grain size of the films and their holes gradually decrease with an increase in the Ni doping amount. The saturation magnetization of \(\hbox {Bi}_{0.85}\hbox {Nd}_{0.15}\hbox {Fe}_{1-x}\hbox {Ni}_{x}\hbox {O}_{3}\) thin films increases with Ni content. However, appropriate Ni doping concentration can decrease the leakage current and enhance the ferroelectric polarization and optical transmittance of the films. Meanwhile, the absorption edge has a slight red shift. \(\hbox {Bi}_{0.85}\hbox {Nd}_{0.15}\hbox {Fe}_{1-x}\hbox {Ni}_{x}\hbox {O}_{3}\) thin films possess better combination properties at a leakage current density of \(4.27 \times \,10^{-9}\hbox { A cm}^{-2}\), ferroelectric polarization of \(28.58\, \upmu \hbox {C cm}^{-2}\), saturation magnetization of \(2.08\hbox { emu cm}^{-3}\) and transmittance of over 85% when the Ni doping concentration, x is 0.05.

Metal and Nonmetal Codoped 3D Nanoporous Graphene for Efficient Bifunctional Electrocatalysis and Rechargeable Zn-Air Batteries.

Developing bifunctional electrocatalysts with high activities and long durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial toward the practical implementation of rechargeable metal-air batteries. Here, a 3D nanoporous graphene (np-graphene) doped with both N and Ni single atoms/clusters is reported. The predoping of N by chemical vapor deposition (CVD) dramatically increases the Ni doping amount and stability. The resulting N and Ni codoped np-graphene has excellent electrocatalytic activities for both the ORR and the OER in alkaline aqueous solutions. The synergetic effects of N and Ni dopants are revealed by density functional theory calculations. The free-standing Ni,N codoped 3D np-graphene shows great potential as an economical catalyst/electrode for metal-air batteries.

Convenient fabrication of Ni-doped SnO2 quantum dots with improved photodegradation performance for Rhodamine B

Doping technology has been proved to be a productive strategy to realize the multi-functionality of materials. Herein, Ni doped SnO2 quantum dots (QDs) are fabricated through a convenient hydrothermal process. In the fabrication process, Vitamin C (VC) acts as a stabilizer to avoid the precipitating of Sn4+(Ni2+), and Na2CO3 serves as a precipitator to react with Sn4+(Ni2+) to produce Ni doped SnO2 QDs. The influence of the Ni doping amount on the photodegradation performance of SnO2 QDs is studied. It was found that the Ni doped SnO2 QDs with Ni/Sn atomic ratio of 1% display the best photocatalytic performace due to the following advantages: (1) the Ni doping can boost light-harvesting and narrow the band gaps of the SnO2 QDs; (2) the SnO2 QDs with ultra small particle size and large specific surface area can supply more reactive centers for photocatalytic reactions. The two important factors contribute to enhancing the photocatalytic performance of the 1% Ni doped SnO2 QDs. As a result, the 1% Ni doped SnO2 QDs photodegrade 91.5% Rhodamine B after being illuminated by solar light for 28 min, obviously surpassing that of their pure counterparts.

Nanocrystalline NixCo(0.5−x)Zn0.5Fe2O4 ferrites: fabrication through co-precipitation route with enhanced structural, magnetic and photo-catalytic activity

A series of Ni-substituted NixCo(0.5−x)Zn0.5Fe2O4 with x = (0.1, 0.2, 0.3, 0.4) spinel ferrites were prepared by co-precipitation method to investigate the effects of Ni compositional variation in the structural, optical, magnetic and photo-catalytic activity. The thermal decomposition of NixCo(0.5−x)Zn0.5Fe2O4 was investigated by TGA/DTA. XRD results revealed that all the samples were single-phase of cubic spinel with Fd-3m space group. The lattice constant and average particle size decreased simultaneously with the increase in Ni doping amount. TEM and SEM analysis showed the monodispersion and cubic-like nanostructure. Two prominent stretching bands were observed in FT-IR spectra around 400–600 cm−1. These two bands confirmed the spinel structure of the prepared nanoparticles. Raman spectroscopy is used to verify that we have synthesized spinel ferrites and determines their phonon modes. The optical study UV–visible is used to calculate the optical band gap energies. The products exhibited the attractive magnetic properties with high saturation magnetization, which were examined by a vibrating sample magnetometer. On the other part, the photocatalytic activity of our compounds was studied using methylene blue as model organic pollutants, where the results showed that an appropriate amount of Ni dopant could greatly increase the amount of hydroxyl radicals generated by the ferrite nanoparticles, which were responsible for the obvious increase in the photo-catalytic activity.

Superior NH3Sensor Using Ni Doped K-OMS-2 Nanofibers

A room temperature reversible ammonia (NH3) gas sensor based on the resistive transduction mechanism comprising of thin film of nickel doped cryptomelane octahedral molecular sieves of K-OMS-2 nanofibers is developed. Ni-OMS2 demonstrated excellent and persistent sensing toward the low concentration of ammonia in air at room temperature. The sensor showed strong response of 20% and 57% for 10 and 50 ppm of NH3. No heating was required either for sensing or recovery. Doping concentration of Ni significantly affect the ammonia sensing properties of nanofibers. Low doping of 0.11 Ni+2 in K-OMS-2 resulted in the major improvement in recovery time during ammonia sensing to 40s from 87s in undoped nanofibers. However, higher amount of Ni doping showed no response for ammonia sensing.

Impact of Ni dopant on structure and electrical properties of PMN-0.1PT ceramics

The Ni-doped PMN-0.1PT (PMN-0.1PT-xNi) relaxor ferroelectric ceramics were prepared by two-step columbite precursor method, and the effects of Ni dopant on the phase structure, dielectric, ferroelectric and electrostrictive properties were systematically investigated. The introduction of Ni dopant significantly improved the densification and grains size in the ceramics, but also profoundly modified the phase structure. It demonstrated that the substitution of Ni dopant for B-site in PMN-0.1PT lattice could affect electrical properties of PMN-0.1PT binary ceramics. Properly increasing the amount of Ni dopant led to the enhancement of dielectric and ferroelectric and remarkably increased the electrostrictive response. Results in this study indicated that at a composition x of 2.0 mol%, a large strain response could be obtained with maximum strain as high as 0.11% under the low field of 15 kV/mm at room temperature.

Local structure studies of Ni doped ZnO/PVDF composite free-standing flexible thin films using XPS and EXAFS studies

Free-standing flexible films of Ni-ZnO/PVDF with three Ni concentrations were obtained by sol–gel technique. The as-deposited and the poled composite Ni-ZnO/PVDF films contained three different amount of Ni doping in ZnO nanocrystals as Zn1−x Ni x O (x = 0.01, 0.04, and 0.09). XANES, XPS measurements have been carried out to investigate the valence states of the host and dopant ions in samples while local environments surrounding Zn and Ni sites have been critically examined using extended EXAFS and XPS measurements to throw a clear insight on the bonding environment in the Ni-ZnO/PVDF films

Dielectric and impedance spectroscopy of Ni doped BiFeO3-BaTiO3 electronic system

A nickel modified BiFeO3–BaTiO3 electronic system has been fabricated by using a high-temperature solid-state reaction process. Preliminary X-ray structural analysis has confirmed the formation of a single-phase material in the orthorhombic crystal system. The dielectric and impedance characteristics of the prepared material have been studied in a wide range of frequency (1 kHz-1 MHz) at different temperatures (25–500 °C) for the better understanding of the frequency-temperature dependence of its capacitive and resistive behavior respectively. A significant effect of grains and grain boundaries of the resistive characteristics of the material is observed at high temperatures. The electrical conductivity of the material increases with increase in frequency in the low-temperature region. Preliminary study of a small amount of Ni doping in the above binary system (i.e., BiFeO3–BaTiO3) has provided many interesting results which may be useful for the fabrication of an electronic device.

Effect of nickel-ion doping in MnO2 nanoneedles as electrocatalyst for the oxygen reduction reaction

In this paper, nickel (Ni)-doped MnO2 nanoneedles were synthesized via a facile hydrothermal method. The effects of nickel doping on structure, morphology and chemical composition of MnO2 nanoneedles were investigated by X-ray diffraction (XRD) spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The XRD patterns proved that nickel doping facilitated the formation of α-MnO2. The role of nickel doping in MnO2 nanoneedles for the oxygen reduction reaction in alkaline media was investigated. The electrocatalytic activities of the nanoneedles were tested by cyclic voltammograms, electrochemical impedance spectroscopy and rotating disk electrode measurements. The electrochemical measurements were operated for the varying amount of Ni doping (Ni atomic ratio of 2.22, 2.76 and 2.90 %) in O2-saturated 0.1 M KOH aqueous solution. The 2.22 % Ni doping MnO2 exhibited higher current density, more positive half-wave potential, lower charge transfer resistance and faster reaction kinetic. Further analysis reveals that the excellent electrocatalytic activity of 2.22 % Ni doping MnO2 is attributed to the increment of Mn(III) as electrochemical active sites.

A comparative study on the structural properties of ZnO and Ni-doped ZnO nanostructures

We investigated the structural properties of zinc oxide (ZnO) nanorods with various Ni doping amounts. The length and diameter of the nanorods decreased and increased, respectively, with increasing Ni doping amount to 5mM. Ni-doped ZnO (Ni-ZnO) nanorods exhibited better crystalline quality than undoped ZnO nanorods. In the visible wavelength region, the optical transmittance of Ni-ZnO nanorods was slightly lower than that of ZnO nanorods. Upon further increasing the Ni doping amount (7mM), the morphology of Ni-ZnO dramatically changed from that of nanorods to a sphere-like structure assembled with interwoven nanowalls. Ni incorporation is a facile strategy for tuning growth behavior and morphology of ZnO nanostructures.

Structure, Morphology, and Electromagnetic Properties of Manganese Dioxide with Ni Doping

Hydrothermal synthesis between (NH 4)2S 2O 8 and MnSO 4 was carried out to investigate the structure, morphology, and electromagnetic properties of Ni-doped MnO 2 with different doping amounts. The samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), and vector network analysis. The analysis results revealed that all the final products were α-MnO 2 and few amounts of γ-MnO 2, and the morphology changed obviously with the increase of the Ni doping amount. The doping of Ni had a certain effect on the electromagnetic properties, and some other properties derived from electromagnetic performances were also investigated, such as dielectric and magnetic loss tangent and microwave-absorbing properties. All the reflection loss (RL) peaks of the final products were moving toward lower frequency with increasing thickness, and with the thickness of 2 mm, the final products all had the maximum effective absorption bandwidth (RL < −10 dB), and the Ni-doped MnO 2 had better reflection loss performance than the undoped MnO 2 in the range of high frequency.