Incorporation Of Ni Ions Research Articles

Low-Temperature Plasma-Assisted Catalytic Dry Reforming of Methane over CeO2 Nanorod-Supported NiO Catalysts in a Dielectric Barrier Discharge Reactor.

Nonthermal plasma (NTP)-assisted catalytic dry reforming of methane (DRM) is considered a powerful single-stage reaction mechanism because of its ability to activate normally stable CO2 and CH4 at a low temperature under ambient conditions. The thermodynamic barrier of DRM requires a high operating temperature (>700 °C), which can be reduced by nonequilibrium plasma. Herein, we present a method for the wet-impregnation synthesis of CeO2 nanorod (NR)-supported 5 and 15 wt % NiO catalysts for efficient NTP-promoted DRM with an applied power in the range of 24.9-25.8 W (frequency: 20 kHz), a CH4:CO2 feed gas ratio of 100:250 sccm, and a total flow rate of 350 sccm. The presence of NTP dramatically increased the reaction activity, even at 150 °C, which is usually inaccessible for thermally catalyzed DRM. The CH4 and CO2 conversion reaches a maximum of 66 and 48%, respectively, at 500 °C with the 15 wt % NiO/CeO2 NR catalyst, which are much higher than the values obtained for the 5 wt % NiO/CeO2 NR catalyst under the same conditions. According to the X-ray photoelectron spectroscopy profile for 15 wt % NiO/CeO2 NR, a higher concentration of NiO on CeO2 increases the proportion of Ce3+ in the catalyst, suggesting enhanced oxygen vacancy concentration with an increased amount of NiO loading. Additionally, a higher NiO loading promotes a higher rate of replacement of Ce4+ with Ni2+, which generates more oxygen vacancies due to the induced charge imbalance and lattice distortion within the CeO2 lattice. As a result, it can be inferred that the incorporation of Ni ions into the CeO2 structure resulted in inhibited growth of CeO2 crystals due to the creation of a NixCe1-xO2-α solid solution and the production of oxygen vacancies.

Polypyrrole Serving as Multifunctional Surface Modifier for Photoanode Enables Efficient Photoelectrochemical Water Oxidation.

Conjugated polymer polypyrrole (PPy) with high electrical conductivity and excellent photothermal effect has been adopted as multifunctional surface modifier on ternary metal sulfide (CdIn2 S4 , CIS) photoanode for photoelectrochemical (PEC) water splitting for the first time. As a p-type conducting polymer, PPy forms p-n junction with n-type CIS to relieve the bulk carrier recombination. Besides, the incorporation of Ni ions into PPy matrix further enhances the surface charge carrier transfer at photoanode/electrolyte interfaces. Furthermore, the excellent photothermal effect of PPy produces heat under near-infrared (NIR) irradiation, which can elevate the temperature of CIS photoanode in situ and further enhance the PEC performance. As a result, the optimum CIS/Ni-PPy photoanode shows an obviously enhanced photocurrent density of 6.07mA cm-2 at 1.23V versus reversible hydrogen electrode under the irradiation of AM 1.5G combined with NIR light, which is the highest among all the CIS based photoanodes reported to date. The synergetic effect of Ni-PPy significantly suppresses the bulk recombination, decreases the carrier transfer resistance, and accelerates the surface water oxidation dynamics, resulting in high carrier injection efficiency over 80% in the measured potential range. The universality of the multifunctional surface modifier strategy has also been confirmed on metal oxide photoanode.

Incorporation of Nickel Ions to Enhance Integrity and Stability of Perovskite Crystal Lattice for High-Performance Planar Heterojunction Solar Cells.

Enhancement of integrity and stability of crystal lattice are highly challenging for polycrystalline perovskite films. In this work, a strategy of incorporation of nickel (Ni) ions is presented to modulate the crystal structure of the CH3NH3PbI3 perovskite film. A broad range of experimental characterizations reveal that the incorporation of Ni ions can substantially eliminate the intrinsic halide vacancy defects, since Ni ions have a strong preference for octahedral coordination with halide ions, resulting in significantly improved integrity and short-range order of crystal lattice. Moreover, it is also demonstrated that the stronger chemical bonding interaction between Ni ions and halide ions as well as organic group can improve the stability of the perovskite material. Simultaneously, the surface morphology of the perovskite thin film is also improved by the incorporation of nickel ions. As a result, a planar heterojunction perovskite solar cell incorporated with 1.5% Ni exhibits a power conversion efficiency of 18.82%, which is improved by 25% compared with 14.92% for the pristine device. Simultaneously, the device formed incorpration of 1.5% Ni shows remarkable stability with 90% of the initial efficiency after storage in an air environment for 800 h. The studies provide a new insight into metal-incorporated perovskite materials for various optoelectronic applications.

Preferential Oxidation of CO in H2-Rich Stream Over Au/CeO2–NiO Catalysts: Effect of the Preparation Method

Two methods, viz., the hydrothermal (HT) and co-precipitation (CP) methods, were used to prepare CeO2–NiO composite oxides; with them as the supports, Au/CeO2–NiO catalysts were prepared by the colloidal deposition method and used in the preferential oxidation (PROX) of CO in H2-rich stream. Various characterization measures such as N2 sorption, XRD, TEM, H2-TPR, Raman spectroscopy and XPS were used to clarify the influence of preparation method on the structure of CeO2–NiO support and the performance of Au/CeO2–NiO catalyst. The XPS and TEM results reveal that the CeO2–NiO(HT) support prepared by hydrothermal method displays a uniform rod-like shape and exposes preferentially the (110) and (100) planes of CeO2, whereas the CeO2–NiO(CP) support prepared by co-precipitation method is composed of nanorods and irregular nanoparticles dominated by (111) facets of CeO2. After deposition of gold, both the Au/CeO2–NiO(HT) and Au/CeO2–NiO(CP) catalysts are alike in the state and size distribution of deposited Au nanoparticles. The H2-TPR results indicate that the presence of Au strongly promotes the reduction of CeO2 in the Au/CeO2–NiO catalyst. Raman spectra illustrate that the incorporation of Ni ions into CeO2 remarkably increases the amount of oxygen vacancies in the CeO2–NiO supports, especially in CeO2–NiO(HT) prepared by hydrothermal method, which is beneficial to the dispersion and stabilization of gold species. The structure of CeO2–NiO support and catalytic activity of Au/CeO2–NiO in CO PROX is strongly related to the preparation method; Au/CeO2–NiO(HT) exhibits much higher activity than Au/CeO2–NiO(CP). The larger fraction of (110) and (100) CeO2 facets in CeO2–NiO(HT) can promote the dispersion of gold species, formation of oxygen vacancies and migration of oxygen species, which are effective to enhance the redox capacity and activity of the obtained Au/CeO2–NiO(HT) catalyst for CO PROX in H2-rich stream. Au supported on CeO2–NiO nanorods prepared by hydrothermal method exhibits much higher catalytic activity for CO PROX in H2-rich stream.

Glycerol steam reforming for hydrogen production: Design of Ni supported catalysts

In this work the activity of Ni catalysts in hydrogen production by glycerol steam reforming was studied. Moreover the effect of the support (TiO2, SBA-15 and ZrO2) on the catalytic performance of Ni was evaluated. A strong effect of the support on the activity of the samples was detected. The Ni/TiO2 sample showed negligible activity mainly due to the low strength of anatase to keep nickel in the reduced state. In fact, both incorporation of Ni ions into the nanoanatase lattice and oxidation of the active phase to NiO under operating conditions were observed. A deactivation process was also found with the Ni/SBA-15 sample while the best results were achieved with the Ni/ZrO2 catalyst, showing no deactivation. After 20h, the glycerol conversion was ∼72% and the H2 yield was ∼65%. The Ni/ZrO2 sample was even more active when tested at lower temperatures, although its performance was less stable. On the basis of the experimental results, it was evidenced that the nature of the support affects above all the stability of the active phase. In particular, strong interactions between the metal active phase and the support ensures stability, activity and selectivity of the catalyst in glycerol steam reforming reactions.

Effect of Ni Doping on the Structure and Magnetic Property in Chemically Synthesized (In1−x Ni x )2 O3 (x = 0.03, 0.05, and 0.07) Nanocrystals

In order to experimentally check the Ni doped In2O3 as a potential spintronic material and to search for high temperature ferromagnetic material, a series of (In1−x Ni x )2O3 (x = 0.03, 0.05, and 0.07) nanoparticles were prepared by sol–gel method. Lattice parameter measurement shows distinct shrinkage of the lattice constant indicating the actual incorporation of Ni ions into the In2O3 lattice. X-ray diffraction (XRD) data show that all the samples exhibit single-phase polycrystalline behavior. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show that the particle size of the calcined powder is in the range of 10–14 nm and 8–9 nm, respectively. SEM energy dispersive x-ray spectrometer (EDS) mapping shows the presence of Ni ions in the Ni doped In2O3 sample. High resolution transmission electron microscopy (HRTEM) micrographs show lattice fringes of 0.290 and 0.322 nm corresponding to the crystallographic plane (222) and (310) of cubic In2O3. Magnetization study indicated that the Ni doped In2O3 samples exhibit diamagnetic behavior.

Nanocomposite Polymeric Microspheres Containing Ni Nanoparticles with Controlled Microstructures

A synthesis method for nanocomposite microspheres containing Ni nanoparticles via chemical surface modification has been developed, by which particle size and interparticle distance for embedded Ni nanoparticles can be systematically controlled. The process relies on introduction of carboxyl acid groups via hydrolysis of matrix polymer, incorporation of Ni ions via ion exchange reaction, hydrogen-induced reduction of doped Ni ions in the sphere followed by Ni nanoparticle-catalyzed decomposition of the surrounding polymer matrix. We demonstrate the formation of Ni nanoparticles in polymer microspheres and structural change of polymer matrix upon reaction by FT-IR, SEM, and cross-sectional TEM studies, and show that initial Ni ion loading determines final nanoparticle size ranging from 3 to 8 nm, which are homogeneously distributed in the whole of the microspheres. The heat-treatment in a hydrogen atmosphere at fixed temperature causes decomposition of the polymer matrix via catalytic reaction of Ni nanoparticles, resulting in a gradual increase in the volume fraction of the Ni phase in the spheres and thus decrease of the average interparticle distance. The process reported herein allows, therefore, one to independently control size and interparticle distance of Ni nanoparticles and is an effective methodology for preparing high-quality nanocomposites with a tailored microstructure which further allows control of functions.

Site-Selective Substitution by Transition Metal Cations for NaCo2O4 via Ion-Exchange

Incorporation of Ni ions into two different sites of the Na and Co sites of NaCo2O4 was carried out by the processes of conventional elemental substitution for Co ion and solid state ion exchange of mobile Na+ ion. The changes of the lattice parameters of “substituted” and “exchanged” samples were different, suggesting that the Ni ions occupy different sites. The Ni-substituted sample for Co showed a significant decrease of Seebeck coefficient keeping the electrical conductivity almost intact, while Ni-exchanged samples for Na showed a lower electrical conductivity than that of the non-substituted sample with keeping the Seebeck coefficient unchanged. These results suggest that Ni cations introduced to the Co site decouples the Co-Co spin exchange, whereas those at the Na site compensates positive holes by providing conduction electrons.