Oxidation State Of Nickel Research Articles

Vacancy-Induced Semiconductor–Insulator–Metal Transitions in Nonstoichiometric Transition Metal Oxides

Metal–insulator transitions in strongly correlated transition metal oxides (TMOs) induced by electrochemical charging have been attributed to formation of vacancy defects. However, the role of native defects in affecting these transitions is not well understood. This presentation will discuss a new type of phase transition in p-type, nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete reversal of conductivity from p- to n-type at room temperature induced by the interaction of native vacancy defects with redox species such as Li+ during electrochemical charging. Direct observation of vacancy-ion interactions using in-situ near-infrared photoluminescence spectroscopy show that this transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li+ insertion into the lattice. Changes in the oxidation states of nickel due to defect interactions probed by X-ray photoemission spectroscopy support the above conclusions. In contrast, n-type, nonstoichiometric tungsten oxide shows only insulator-to-metal transition, which is a result of oxygen vacancy formation. The defect-property correlations shown here in these model systems can be extended to other oxides to enable rational engineering of a new robust class of nanoscale, low temperature TMO catalysts and sensors having tailored functionality and selectivity.

Carbon-Carbon Bond-Forming Reductive Elimination from Isolated Nickel(III) Complexes.

This manuscript describes the design, synthesis, characterization, and reactivity studies of organometallic NiIII complexes of general structure TpNiIII(R)(R1) (Tp = tris(pyrazolyl)borate). With appropriate selection of the R and R1 ligands, the complexes are stable at room temperature and can be characterized by cyclic voltammetry, EPR spectroscopy, and X-ray crystallography. Upon heating, many of these NiIII compounds undergo C(sp2)-C(sp2) or C(sp3)-C(sp2) bond-forming reactions that are challenging at lower oxidation states of nickel.

XAFS Study of Iron and Nickel Speciation in Complex Sodium Aluminophosphate Based Glasses

Iron and nickel oxidation state and coordination in complex sodium aluminophosphate based glasses suggested as potential matrices for immobilization of legacy high level waste currently stored in stainless steel tanks at PA «Mayak» (Ural reg., Russia) were determined by X-ray absorption fine structure spectroscopy (XAFS: XANES/EXAFS). The glasses containing (wt.%) 20-30 Na2O, 6-12 Al2O3, 40-52 P2O5, 2-5 Fe2O3, 1-3 NiO, 0-6 B2O3, 10-15 other waste oxides produced by quenching of their melts were fully amorphous or contained minor Fe and Ni free phases. Fe in the glasses was found to be predominantly trivalent with an average Fe-O distance and a coordination number (CN) in the first shell of 1.94 to 1.97 A and 5.2 to 5.8, respectively, mostly in octahedral oxygen environment. Ni is divalent in all the glasses and has in the first shell an average Ni-O distance and CN of 1.97 to 2.03 A and 4.9 to 5.6, respectively. The first shell of both Fe and Ni is somewhat distorted. The second and further coordination shells are weakly appeared exhibiting no clustering and homogeneous distribution of Fe and Ni ions in the glass network. The data on Fe obtained are in good agreement with those from Mossbauer study of same glasses. After annealing glasses were partly devitrified and interpretation of XAFS data is strongly complicated due to Fe and Ni partitioning among crystalline and vitreous phases.

Vacancy-Induced Semiconductor-Insulator-Metal Transitions in Nonstoichiometric Nickel and Tungsten Oxides.

Metal-insulator transitions in strongly correlated oxides induced by electrochemical charging have been attributed to formation of vacancy defects. However, the role of native defects in affecting these transitions is not clear. Here, we report a new type of phase transition in p-type, nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete reversal of conductivity from p- to n-type at room temperature induced by electrochemical charging in a Li+-containing electrolyte. Direct observation of vacancy-ion interactions using in situ near-infrared photoluminescence spectroscopy show that the transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li+ insertion into the lattice. Changes in the oxidation states of nickel due to defect interactions probed by X-ray photoemission spectroscopy support the above conclusions. In contrast, n-type, nonstoichiometric tungsten oxide shows only insulator-to-metal transition, which is a result of oxygen vacancy formation. The defect-property correlations shown here in these model systems can be extended to other oxides.

Cracking the Genetic Code of Nickel on the Performance of the High Energy Layered Cathode Materials

Recently, the LiMO2 layered cathode material has been playing a pivotal role in the field of lithium ion battery. There have been many attempts to combine various types of atoms in layered system to discover enhanced electrochemical performance cathode materials, and three-component system (Nickel, Cobalt, and Manganese) has gained the most interests among them. Specifically, a study of increasing the Ni content in the atomic combination becomes popular trend in order to obtain advanced cathode materials with higher capacity. However, there has not been a clear elucidation on the fundamental role of nickel element in the three-component layered system yet. Thus, the Co fixed LiNi0.5+xCo0.2Mn0.3-xO2 (x=0, 0.1, 0.2) layered materials were designed to unravel the role of Ni atom as a major contributor to the crystallographic and electrochemical nature of Ni-rich layered materials. The results, on the basis of synchrotron-based characterization techniques, present a decreasing trend of Ni2+ content in Li layer with increasing total Ni contents in the Co fixed LiNi0.5+xCo0.2Mn0.3-xO2 (x=0, 0.1, 0.2) layered materials unlike the previously reported trend, and it disabuses the misapprehension of cation mixing in Ni-rich cathode materials. Moreover, it is discovered that a c-axis parameter of layered system is not intimately related with the real lithium ion pathway. The lithium inter-slab space increases with growing level of nickel concentration even though the c-axis parameter decreases. To investigate the structural behavior of Co fixed cathode materials during charge/discharge (de-intercalation/intercalation) process, a synchrotron-based in situ XRD technique was used. The overall structure behavior is similar to each other; however, the degree of phase transition is different depending on the nickel content. The NCM721(x=0.2) cathode material exhibited a smooth phase transition having similar lattice parameter between H1 and H2 phase. For NCM523(x=0), however, the new emerged H2 phase started to be formed exhibiting large disparities of lattice parameter between H1 and H2 phase relatively to the higher nickel content materials. To find out the whole relative integrated peak intensity of H1 and H2 phase in each material during the de-intercalation process, the fitting of (113) reflection was performed. Based on this result, the oxidation states of nickel in each phase are analogized by simplifying some values which are matched with the trend of the experimental result, and then XRD patterns are simulated to evaluate the suitability of the hypothesis. As the nickel content increases, the gap of oxidation state between H1 and H2 phase is narrowed down. According to this trend, The NCM721 has recorded the highest lithium diffusion coefficient and the lowest over-potential on the whole during the de-intercalation process, and then NCM622, NCM523 in this sequence. The NCM523 cathode material has higher Ni2+ content in the Li layer and narrower lithium inter-slab space compared to higher nickel content cathode material such as NCM622 which is even more Ni2+ content in the Li layer and narrower lithium inter-slab space than NCM721. Following this trend, the XRD patterns during the de-intercalation process also showed a distinctive trend. In relation to this, a higher nickel content material shows better electrochemical performance in terms of capacity and cycling behavior compared with lower ones.

Elucidating the Synergetic Mechanism of Ni-Mo Electrocatalysts for the Hydrogen Evolution Reaction

Hydrogen is a potential future energy vector and a current industrial feedstock. Currently, most hydrogen is produced through the fossil fuel dependent steam reforming reaction. Water electrolysis is a promising alternative, but is currently limited by the availability of non noble metal catalysts that are stable in acid and by the lack of highly active non-noble metal catalysts in base. Nickel based electrcatalysts are a promising option for active catalysts in base. While it is well known that molybdenum enhances the activity of nickel catalysts, the heterogeneous nature of electrode surfaces complicates efforts to gain a fundamental understanding of this enhancement. In our work, we create a series of electrodes by depositing three different sizes of nickel nanoparticles onto molybdenum substrates. This allows us to investigate the effect that distinct domains of molybdenum, rather than an alloy or co-deposited material, has on nickel. We find that the activity is highest for the largest particles, a result that suggests that the enhancement is not occurring solely at the interface. As it is been demonstrated that the coexistence of multiple nickel oxidation states in pure nickel systems increases activity, we posit that the molybdenum acts to maintain the requisite plurality of oxidations states on the nickel nanoparticles.

Distorted tetrahedral nickel-nitrosyl complexes: spectroscopic characterization and electronic structure.

The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitrogen-based ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3), was prepared by the reaction of the potassium salt of the ligand with the nickel-nitrosyl precursor [Ni(NO)(Br)(PPh 3 ) 2 ]. The obtained nitrosyl complexes as well as the corresponding chlorido complexes [Ni(NO)(Cl)(PPh 3 ) 2 ] and [Ni(Cl)(L3)] were characterized by X-ray crystallography and different spectroscopic methods including IR/far-IR, UV-Vis, NMR, and multi-edge X-ray absorption spectroscopy at the Ni K-, Ni L-, Cl K-, and P K-edges. For comparative electronic structure analysis we also performed DFT calculations to further elucidate the electronic structure of [Ni(NO)(L3)]. These results provide the nickel oxidation state and the character of the Ni-NO bond. The complex [Ni(NO)(L3)] is best described as [Ni (II) (NO (-) )(L3)], and the spectroscopic results indicate that the phosphane complexes have a similar [Ni (II) (NO (-) )(X)(PPh 3 ) 2 ] ground state.

A Heterobimetallic W-Ni Complex Containing a Redox-Active W[SNS]2 Metalloligand.

The tungsten complex W[SNS]2 ([SNS]H3 = bis(2-mercapto-4-methylphenyl)amine) was bound to a Ni(dppe) [dppe = 1,2-bis(diphenylphosphino)ethane] fragment to form the new heterobimetallic complex W[SNS]2Ni(dppe). Characterization of the complex by single-crystal X-ray diffraction revealed the presence of a short W-Ni bond, which renders the complex diamagnetic despite formal tungsten(V) and nickel(I) oxidation states. The W[SNS]2 unit acts as a redox-active metalloligand in the bimetallic complex, which displays four one-electron redox processes by cyclic voltammetry. In the presence of the organic acid 4-cyanoanilinium tetrafluoroborate, W[SNS]2Ni(dppe) catalyzes the electrochemical reduction of protons to hydrogen coincident with the first reduction of the complex.

The Reduction of Beta-NiOOH on the Cathode of Nickel Hydrogen Battery Due to the Local Cell Reaction

Introduction Recently, nickel hydrogen battery is taking a great attention as the most promising candidate for power sources of hybrid vehicles. Therefore, it is important to develop a property of nickel hydrogen battery. When nickel hydrogen battery is cycled at a shallow depth of discharge, the cell capacity degrades in comparison with that after normal discharge-charge cycles[1]. Sato et al. reported that the formation of γ-NiOOH (oxidant of β-NiOOH) is the major factor of such capacity degradation, and that γ-NiOOH formation doesn't occur from the interface between electrolyte and β-NiOOH but from the interface between current collector (CC) and cathode active material (β-NiOOH)[2]. However, the precise mechanism of γ-NiOOH formation from CC side is not clarified. We focused attention to the local cell reaction (LCR) taking place at the interface of β-NiOOH and CC in the open circuit[3]. In the previous study, by employing various metals as CC, we investigated about the difference of LCR and the effect on the battery performance. We revealed that the degradation of cell capacity occurs only when nickel mesh CC is used and no degradation occurs when gold or platinum mesh is used. In addition, we also found that the degraded sample shows a XRD peak between 10° and 15° in 2θ[4,5]. In this study, we investigated the oxidation state of nickel in NiOOH by XPS measurement to verify that the product of LCR is the reductant of β-NiOOH. Experiment We fabricated the cathode by mixing powder of the synthesized β-NiOOH, acetylene black and PTFE at the ratio of 80:15:5 by weight. Platinum plate was used as counter electrode and Ag/AgCl electrode was used as reference. The electrolyte was an 8M potassium hydroxide. We used nickel, platinum and gold mesh as CC to investigate the difference of changes in the oxidation state of nickel in NiOOH due to LCR. We discharged the cell to the cutoff voltage of 0.19 V (vs. SHE) and then charged for 6h. We repeated this process for 3 times to stabilize the cell reaction. After the stabilization, we discharged the cell to SOC 40% or 20%. Then, we conducted the charge-discharge cycles with rest time period at the every end of charge to cause LCR during rest. For the charge-discharge cycles with rest, the cell was charged for 50 minutes, take rest for 2 h, discharged for 40 minutes and this cycle was repeated, i.e., we conducted the cycles with rest between SOC 40-60% and that between SOC 20-40%. All of the charge-discharge cycles were conducted at 30mA/g. We also conducted XRD measurement of the surface of cathode using RINT-TTR (Rigaku co., CuKα, 200 mA, 30 kV) to investigate the change of crystal structure and XPS measurement of cathode using ESCA-3400 (Shimadzu co., MgKα, 1253.6 eV) to check the oxidation state of nickel in NiOOH. Results and Discussion Fig.1 shows the discharge curves in charge-discharge cycles with rest at SOC 40-60% region. Fig.1 (a), (b) and (c) represent the results for nickel, platinum, and gold mesh CCs, respectively. Fig.2 also represents the corresponding X-ray diffraction results. When we use platinum or gold mesh with higher potential than β-NiOOH, the reduction of β-NiOOH doesn’t occur and the capacity loss is not observed after 50th cycle. On the other hand, when we use nickel mesh with lower potential than β-NiOOH, β-NiOOH acts as cathode and CC acts as anode in LCR, and consequently, the reduction of β-NiOOH occurs. We named the reductant of β-NiOOH as γ´-NiOOH which is different from γ-NiOOH. Due to the formation of γ´-NiOOH, the capacity loss and the XRD peak are observed between 10° and 15° in 2θ after 35th cycle as depicted by arrow in Fig.2 (a). Fig.3 shows the results for XPS measurement and (a), (b) and (c) represent the results for nickel, platinum, and gold mesh, respectively. Only when we use nickel mesh, the chemical shift of Ni 2p XP spectrum indicating the reduction of nickel in β-NiOOH is observed. Considering the results for Fig.1 and Fig.2, it is verified that the γ´-NiOOH is the reductant of β-NiOOH. It is concluded that our local cell reaction model for the capacity loss due to the γ´-NiOOH formation is consistent with our present experimental results.

Accessing Pincer Bis(carbene) Ni(IV) Complexes from Ni(II) via Halogen and Halogen Surrogates.

This communication describes the two-electron oxidation of ((DIPP)CCC)NiX ((DIPP)CCC = bis(diisopropylphenyl-benzimidazol-2-ylidene)phenyl); X = Cl or Br) with halogen and halogen surrogates to form ((DIPP)CCC)NiX3. These complexes represent a rare oxidation state of nickel, as well as an unprecedented reaction pathway to access these species through Br2 and halogen surrogate (benzyltrimethylammonium tribromide). The Ni(IV) complexes have been characterized by a suite of spectroscopic techniques and can readily reduce to the Ni(II) counterpart, allowing for cycling between the Ni(II)/Ni(IV) oxidation states.

The role of phosphine and 1,2-diimine complexes of nickel in the oxidation states 0, +1, and +2 in the catalyzed di-, oligo-, and polymerization of ethylene

The turnover frequency and number have been determined for eighteen catalytic systems based on triphenylphosphine and 1,4-diazo-1,3-butadiene complexes of nickel in the formal oxidation states 0, +1, and +2 in the oligoand polymerization of lower alkenes. The main catalytic characteristics are almost independent of the oxidation state of nickel in the precursor and depend on the nature and concentration of the cocatalyst (Lewis acid). The catalytic systems have been studied by ESR. The ESR spectral parameters are presented for nickel(I) 1,4-diazo-1,3-butadiene complexes and radical anions resulting from the reactions of the cocatalyst with nickel α-diimine complexes. Reactions describing the formation, functioning, decomposition, and regeneration of the catalytically active nickel hydride complexes are proposed.

Ba-doping effects on structural, magnetic and vibrational properties of disordered La2NiMnO6

Barium-doped La2NiMnO6 double perovskites have been investigated in order to elucidate the role of the B-site doping on its magnetic, dielectric and vibrational properties. In all cases, we have obtained a non-linear dependence with the Barium content signaling that a 5% molar doping renders the maximum B-site ordering. By analyzing a series of gradually doped samples, we have found that the effective magnetic moment in the B-site can be enhanced by a factor of nearly 100% by 5% Ba doping. In order to exclude oxidation state induce changes, XPS and XANES measurements have been carried out concluding that nickel or manganese oxidation states ratio are not modified by the Ba doping. Raman spectroscopy correlates Ba doping with vacancies thus attributing to the latter the role of primary source for structural defects in Ba–La2NiMnO6 samples. This manuscript summarizes key consequences of the B-site ordering which are crucial to address the optimization of the magneto-electric coupling in Ba–La2NiMnO6 double perovskites.

Influence of Oxidation State of Nickel Supported on TiO<sub>2</sub> on Gas-Phase Hydrogenation of Acetonitrile

Influence of Oxidation State of Nickel Supported on TiO<sub>2</sub> on Gas-Phase Hydrogenation of Acetonitrile

Effect of nickel oxidation state on the structural and electrochemical characteristics of lithium-rich layered oxide cathodes

Increasing the Ni oxidation state in Li-rich layered oxides enhances the cyclability and reduces the voltage decay due to a decreased degree of Mn4+ reduction and layered-to-spinel transformation.

Profiling the nanoscale gradient in stoichiometric layered cathode particles for lithium-ion batteries

Chemical and structural evolution in battery materials influences properties relevant to ionic and electronic transport and ultimately impacts the battery performance. Although chemical and structural gradients have been observed in several cathode materials, the origin(s) of these phenomena are poorly understood. Via high-throughput core-level spectroscopies {i.e., X-ray absorption spectroscopy (XAS), depth-profiled X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS)}, as well as scanning transmission electron microscopy (STEM), the present study seeks to achieve mechanistic understanding for these phenomena in a stoichiometric Rm layered cathode material (e.g., LiNixMnxCo1−2xO2, NMC). We observed that the surfaces of particles in the composite electrode are complicated by the presence of a surface reaction layer resulting from electrolyte decomposition. In large particle ensembles, the global nickel oxidation state switches between Ni2+ and Ni2+x (x = 1–2) during charging/discharging processes, and hole states are also created at the O2p level due to the TM3d–O2p hybridization states. In primary particles, the surface is less oxidized than the bulk counterpart of the same particle whenever the particle has been cycled. This is partially attributed to the reconstruction from an Rm structure to an Fmm structure at the surfaces of NMC particles. This work provides a unique insight into correlating crystal structures with charge compensation mechanisms and performance fading in stoichiometric layered cathode materials.

Structural position and charge state of nickel in SrTiO3

The properties of Ni-doped strontium titanate are studied using X-ray diffraction and XAFS spectroscopy. It is shown that regardless of the preparation conditions, the SrTi1-xNixO3 solid solution and the NiTiO3 phase are the most stable phases which can coexist. According to the EXAFS data, in the single-phase sample of SrTi0.97Ni0.03O3, the Ni atoms substitute for the Ti ones and are on-center. The distortion of the oxygen octahedra is not observed. The XANES spectra analysis shows that the oxidation state of nickel in NiTiO3 is 2+, and in the SrTi1-xNixO3 solid solution it is close to 4+. It is shown that the strongest light absorption in doped samples is associated with the presence of tetravalent nickel in the SrTi1-xNixO3 solid solution. This doping seems the most promising one for solar energy converters that exploit the bulk photovoltaic effect.

Structural characterization and electrochemical intercalation of Li+ in layered Na0.65Ni0.5Mn0.5O2 obtained by freeze-drying method

New data on the structure and reversible lithium intercalation properties of sodium-deficient nickel–manganese oxides are provided. Novel properties of oxides determine their potential for direct use as cathode materials in lithium-ion batteries. The studies are focused on Na x Ni0.5Mn0.5O2 with x = 2/3. Between 500 and 700 °C, new layered oxides Na0.65Ni0.5Mn0.5O2 with P3-type structure are obtained by a simple precursor method that consists in thermal decomposition of mixed sodium–nickel–manganese acetate salts obtained by freeze-drying. The structure, morphology, and oxidation state of nickel and manganese ions of Na0.65Ni0.5Mn0.5O2 are determined by powder X-ray diffraction, SEM and TEM analysis, and X-ray photoelectron spectroscopy (XPS). The lithium intercalation in Na0.65Ni0.5Mn0.5O2 is carried out in model two-electrode lithium cells of the type Li|LiPF6(EC:DMC)|Na0.65Ni0.5Mn0.5O2. A new structural feature of Na0.65Ni0.5Mn0.5O2 as compared with well-known O3–NaNi0.5Mn0.5O2 and P2–Na2/3Ni1/3Mn2/3O2 is the development of layer stacking ensuring prismatic site occupancy for Na+ ions with shared face on one side and shared edges on the other side with surrounding Ni/MnO6 octahedra. The reversible lithium intercalation in Na0.65Ni0.5Mn0.5O2 is demonstrated and discussed.

A Catalyst with Two‐Coordinate Nickel: Theoretical and Catalytic Studies

AbstractThe bisadduct (cAAC)2NiIICl2 [1; cAAC = cyclic (alkyl)(amino)carbene] was directly synthesized by treating cAAC with NiCl2. Compound 1 was reduced to (cAAC)2Ni0 (2) by using lithium diisopropylamide or KC8. Crystals of 2 were stable under an inert gas for several months and decomposed upon heating above 165 °C. On the basis of the calculated natural bond orbital charge values of the nickel atom in 2, the oxidation state of nickel was determined to be between NiI and Ni0 (+0.34). Theoretical calculations suggested a closed‐shell singlet electronic configuration of 2 with little biradical character. Ab initio multiconfigurational C(R)ASSCF/CASPT2 calculations predicted a closed‐shell singlet electronic configuration (Ni0), whereas excited spin states possessed NiI character with unpaired electrons on neighboring carbon atoms. The catalytic activity of complex 2 was investigated for the homocoupling of various unactivated aryl chlorides/fluorides. The biaryls were obtained in good yields at moderate temperature. Theoretical studies showed that an intermediate containing NiIII was more favored than one with NiIV.

Spectroscopic and Quantum Chemical Study of the Ni(PPh2NC6H4CH2P(O)(OEt)22)2 Electrocatalyst for Hydrogen Production with Emphasis on the NiI Oxidation State

The bis(diphosphine)nickel catalyst first investigated by DuBois and co-workers [DuBois, M. R.; DuBois, D. L. Chem. Soc. Rev. 2009, 38, 62] is arguably one of the most promising molecular catalysts for hydrogen production. It features a low overpotential and, in its most recent variation, a high turnover number of 105 s–1 [Helm, M. L.; Stewart, M. P.; Bullock, R. M.; DuBois, M. R.; DuBois, D. L. Science 2011, 333, 863]. The complex features two reversible one-electron reductions. It is believed that all accessible oxidation states (2+, 1+, 0) of nickel are involved in the proposed catalytic cycle. In this article we focus on the paramagnetic NiI state, for which few experimental studies have been performed. By a combination of modern EPR and quantum chemical methods, it is established that the stable NiI species does not feature a hydride ligand. Furthermore, hydrogen evolution already starts upon addition of acid to the NiI state even without the presence of additional reducing equivalents. The implications for the catalytic cycle are discussed.

Nickel Oxidation States and Spin States of Bioinorganic Complexes from Nickel L-edge X-ray Absorption and Resonant Inelastic X-ray Scattering

Soft X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) have been performed on several nickel-containing bioinorganic complexes. RIXS spectral features are shown to ...