Ni K-edge Research Articles

(Invited) Atomic View of Nickle Dithiolene Electro- and Photo-Catalysis Using X-Ray Absorption Spectroscopy

Metal dithiolenes are a class of molecular catalysts known for their redox-active ligands and their efficient and robust electro- and photo-catalysis of the hydrogen evolution reaction. To understand how the redox-active ligands of these catalysts participate in their chemical reactions, we need atom-specific probes of charge and bonding at both metal and ligand atomic sites. X-ray absorption spectroscopy (XAS) affords us this opportunity and is used to study the electro- and photo-catalytic reaction mechanisms of these complexes, with a specific focus on the role of metal versus ligand atomic sites. Static soft x-ray XAS studies of Nickle dithiolene catalysts at the Ni L-edge and S K-edge will be presented to resolve the electronic structure of these complexes. Static and transient XAS of Nickle aminothiolate complexes at the Ni K-edge will be presented to resolve their electro- and photo-catalytic reaction mechanisms. These results highlight the unique ability of x-ray spectroscopy to clarify the role of redox-active ligands during catalysis.

Thermal Stability Analysis of NMCs with Various Co Concentrations

INTRODUCTION Lithium ion batteries(LIBs) are used widely ,expanding in application. LIB's safety is urgent problem to be solved before practical use of large scale battery for automobiles. Although there are many factors to trigger so-called "thermal-runway" at elevated temperature, positive electrode material is one of the most important factors because oxygen is released by the decomposition of the cathode active material's crystal structure. In addition to the safety problem, recent rise in cobalt prices has also become a big problem, because cobalt is commonly used in the commercial positive electrode materials.It is important to obtain the guidance for designing oxide cathode active materials to satisfy both of safety and cost down. NMC, cathode including -Ni, Mn and Co, becomes less stable at elevated temperatures, and the tendency becomes obvious with the increase of Ni concentration 1). The purpose of this study is to reveal how thermal stability changes with constant Ni content and decreasing Co concentrations in NMCs(532, 541, 550). In this study,we prepared three NMCs and its chemically delithiated compounds, to obtain the thermal behavior of cathode active material only. EXPERIMENTAL Three NMC samples were obtained by coprecipitation-calcination method. The calcination condition was fixed at 850ºC for 5h in air. Chemically delithiated Li0.3MO2(M=Ni, Co, Mn) are obtained through the reaction with oxidizer (NO2BF4)2) from NMCs in various Co concentrations(532, 541, 550). The chemical composition of the delithiated samples were determined by ICP-AES. TPD-MS was performed for these delithiated samples to analyze amount and behavior of oxygen release during heating process, and in situ XRD at elevated temperature was conducted to analyze crystal structure, and fine structure around transition metals were analyzed by FT-EXAFS. RESULTS AND DISCUSSION Oxygen release has detected roughly in two temperature regions(Fig.1), one is around 300ºC, denoted as region 1, and the other is around 450ºC, denoted as region 2. Total amount of oxygen release decreased with decreasing Co concentration (NMC532 > 541> 550) in cathode active materials, that is, the total amount of oxygen release is smallest in NMC550. It suggests NMCs with lower Co concentrations have lower oxygen evolution and higher thermal stability.In the region 1, peak top temperature was detected higher in order of lower Co concentrations(532<541<550), but on the other hand, in the region 2, peak top temperature was not in order of Co concentration, that is, the order of peak top temperature is 532,550 < 541.To reveal the reason why thermal stability is different due to the Co concentrations, we analyzed structural change using XRD and FT-EXAFS at elevated temperature. XRD indicates that layered rock salt structure changes into spinel structure mainly in region 1 and spinel into rock salt structure in region 2, which is common behavior in all samples. Focusing on (003) diffraction peak, 550 and 541 have a clear shoulder peak at higher angle at 200ºC. These shoulders imply that there are 2 layered rock salt phases wtih the different Li occupancies (Li-rich and Li-poor). In the process of heating, these shoulders disappeared at 350ºC in 550 and 541. This shoulder was not clearly detected in 532 through heating. So, the appearance of shoulder peak differs due to the Co concentrations. Ni K-edge FT-EXAFS spectra showed that layered rock salt structure changes into spinel structure mainly in region 1 and the spinel structure into rock salt structure in region 2, in all samples. From Co K-edge FT-EXAFS spectra show that the layered rock salt structure does not clearly change in region 1, but changes into Co3O4-type spinel in region 2, which is the same behavior for 532 and 541. Mn K-edge FT-EXAFS spectra show different behavior depending on the Co concentration. Over 300ºC, the peak shift around 4.5～5.5Å was detected in 532 and 541, which suggests that lithiation into layered rock salt. In contrast, over 300ºC, the peak intensity at around 2.5Å increased in 550 and 541, which is identified as LiMn2O4. Therefore, It is concluded that the difference of thermal stability was explained by reconstruction around Mn-rich domain, the generation of LiMn2O4, and decomposition around Co and Ni-rich domain, both of which results in the appearance of lithiated structure. These structural change cause O2 generation depending on temperature region. So,we need to design cathode both in the view points of O2-release amount and generation temperature to maintain the balance of safety and cost down. References 1)Xiqian Yu et al., Chin. Phys. B. Vol.25, No.1 (2016), 018205 2)S. Venkatraman and A. Manthiram, Chem. Mater. 2002, 14, 3907-3912 Figure 1

A general bimetal-ion adsorption strategy to prepare nickel single atom catalysts anchored on graphene for efficient oxygen evolution reaction

Abstract Single-atom catalysts (SACs) supported on two-dimensional (2D) materials are highly attractive for maximizing their catalytic activity. However, graphene based SACs are primarily bonded with nitrogen and carbon sites, resulting in poor performance for the oxygen evolution reaction (OER). Herein, we develop a general bimetal-ion adsorption strategy for the synthesis of individually dispersed Ni SACs anchored on the oxygenated sites of ultrathin reduced graphene oxide as efficient OER electrocatalysts. The resultant Ni SACs for OER in alkaline electrolyte exhibit a highly stable overpotential of 328 mV at the current density of 10 mA cm−2, and Tafel slope of 84 mV dec−1 together with long-term durability and negligible degradation for 50 h, which is greatly outperform its counterparts of nitrogen bonded Ni SACs (564 mV, 364 mV dec−1) and Ni(OH)2 nanoparticles anchored on graphene (450 mV, 142 mV dec−1), and most reported Ni based OER electrocatalysts. Furthermore, the extended X-ray absorption fine structure at the Ni K-edge and theoretical simulation reveal that the nickel-oxygen coordination significantly boost OER performance. Therefore, this work will open numerous opportunities for creating novel-type 2D SACs via oxygen–metal bonding as highly robust OER catalysts.

Nickel and iron partitioning between clay minerals, Fe-oxides and Fe-sulfides in lagoon sediments from New Caledonia

In the tropics, continental weathering and erosion are major sources of trace metals towards estuaries and lagoons, where early diagenesis of sediments may influence their mobility and bioavailability. Determining trace metals speciation in tropical sedimentary settings is thus needed to assess their long-term fate and potential threat to fragile coastal ecosystems. In this study, we determined Fe, Ni and S speciation across a shore-to-reef gradient in sediments from the New Caledonia lagoon that receive mixed contribution from lateritic (iron-oxyhydroxides and clay minerals), volcano-sedimentary (silicates) and marine (carbonate) sources. Sulfur K-edge XANES data indicated a major contribution of pyrite (FeS2) to S speciation close to the shore. However, this contribution was found to dramatically decrease across the shore-to-reef gradient, S mainly occurring as sulfate close to the coral reef. In contrast, Fe and Ni K-edge XANES and EXAFS data indicated a minor contribution of pyrite to Fe and Ni speciation, and this contribution could be evidenced only close to the shore. The major fractions of Fe and Ni across the shore-to-reef gradient were found to occur as Ni- and Fe-bearing clay minerals consisting of smectite (~nontronite), glauconite and two types of serpentines (chrysotile and greenalite/berthierine). Among these clay minerals, greenalite/berthierine, glauconite and possibly smectite, were considered as authigenic. The low contribution of pyrite to trace metals speciation compared to clay minerals is interpreted as a result of (1) a reduced formation rate due to the low amounts of organic carbon compared to the Fe pool and (2) repeated re-oxidation events upon re-suspension of the sediments top layers due to the specific context of shallow lagoon waters. This study thus suggests that green clay authigenesis could represent a key process in the biogeochemical cycling of trace metals that are delivered to lagoon ecosystems upon continental erosion and weathering.

Self-supported Ni(OH)2/MnO2 on CFP as a flexible anode towards electrocatalytic urea conversion: The role of composition on activity, redox states and reaction dynamics

Nickel-based catalysts accomplish the direct conversion of urea to pure hydrogen via electrochemical oxidation; yet mechanistic understanding is lacking. Synthesizing a series of carbon fiber paper (CFP) supported Ni(OH)2/MnO2 catalysts, we explored relevant redox transitions and catalysis of both UOR (urea oxidation reaction, in KOH-with-urea) and OER (oxygen evolution reaction, in KOH). Cyclic Voltammetry (CV) in KOH-only solution demonstrated a more cathodic transformation from Ni(III/IV) to Ni(II) compared with that in KOH-with-urea solution. The water oxidation overpotential was shifted to higher values (from 0.48 to 0.53 VRHE) as the Mn:Ni atom ratio increases in CFP-NiMn films. In contrast, a higher Mn content results in higher UOR activity and lower onset potential in KOH solution containing urea (1.395–1.375 VRHE). Quasi in-situ, freeze-quench X-ray absorption spectroscopy (XAS) at the Ni and Mn K-edges was employed to uncover oxidation state changes as well as structural transformations at the atomic level showing that CFP-Ni(OH)2 underwent oxidation state changes by about 1.15 e− and 0.21 e− per Ni ion during OER and UOR processes, respectively, versus only 0.71 e− and 0.07 e− per Ni ion in CFP-NiMn2.4. Mn incorporation can stabilize the Ni in lower valent states in a mixed NiMn catalyst without significant changes in oxidation state and structure. The here investigated, readily synthesized CFP-NiMn films exhibit opposite activity trends in KOH and KOH-with-urea electrolytes: Mn incorporation depresses water oxidation, but it promotes the urea oxidation process. We propose that the water oxidation rate (OER) is positively correlated with the capacity for accumulation of Ni and Mn oxidation equivalents, while the urea oxidation (UOR) rate is negatively correlated with this capacity. Our work offers a mechanistic guideline for designing and synthesizing nonprecious metal-coupled Ni-based catalysts with appropriate redox-properties for urea-oxidation applications.

Nickel tolerance and toxicity mechanisms in the halophyte Sesuvium portulacastrum L. as revealed by Ni localization and ligand environment studies.

Halophytes are able to tolerate relatively high concentrations of hazardous metals in a growing substrate, what makes them suitable candidates for phytoremediation of metal-contaminated soils. In this work, we aimed to study the physiological responses of the halophyte Sesuvium portulacastrum L. to Ni, with main focus on Ni localization, compartmentation and ligand environment, to decipher Ni tolerance and toxicity mechanisms. Seedlings were grown in hydroponic nutrient solution containing 0, 25, 50 and 100μM Ni as NiCl2 for 3weeks. Ni localization in leaves was assessed by micro-proton-induced X-ray emission (micro-PIXE). Ni ligand environment was studied by Ni K-edge X-ray absorption near edge structure (XANES). In addition, Ni-soluble, weakly bound/exchangeable and insoluble leaf tissue fractions were determined by sequential extraction. Results show that S. portulacastrum is able to tolerate up to ~ 500μgg-1 dry weight (DW) of Ni in the shoots without significant growth reduction. At higher Ni concentrations (> 50μM Ni in nutrient solution), chloroses were observed due to the accumulation of Ni in photosynthetically active chlorenchyma as revealed by micro-PIXE. Water storage tissue represented the main pool for Ni storage. Incorporation of Ni into Ca-oxalate crystals was also observed in some specimens, conferring tolerance to high leaf Ni concentrations. The majority of Ni (> 70%) was found in soluble tissue fraction. Ni K XANES revealed Ni bound mainly to O- (55%) and N-ligands (45%). Ni toxicity at higher Ni levels was associated with Ni binding to amino groups of proteins in cytosol of chlorenchyma and increased level of lipid peroxidation. Proline levels also increased at high Ni exposures and were associated with Ni-induced oxidative stress and alteration of water regime.

Thermally activated nucleation and growth of cobalt and nickel oxide nanoparticles on porous silica

Integrating mesoscale to the molecular level understanding of nanoparticle nucleation phenomena can drive the bottom-up synthesis approach for target applications. The authors studied the thermal evolution of binary metal oxide (cobalt and nickel oxides) nanoparticle structural phases on porous silica host from over wide spatial scale using multimodal analysis involving scanning transmission electron microscopy, x-ray absorption near-edge spectroscopy (XANES), and nuclear magnetic resonance (NMR) spectroscopy along with density functional theory (DFT) based calculations. The TEM analysis reveals thermally activated nanoparticle clustering and subsequent interaction with the porous host material. The Co and Ni K-edge XANES spectra revealed the evolution from metal hydroxide to metal oxide and subsequently metal silicate composites with calcination temperature. 29Si NMR analysis revealed the role of surface functional groups of silica host for silicate composite formation, which is corroborated by DFT studies.

Anharmonicity in elastic constants and extended x-ray-absorption fine structure cumulants

We have investigated temperature dependence of the elastic constants and higher-order EXAFS (extended x-ray-absorption fine structure) cumulant moments, both of which originate from vibrational anharmonicity. We focus our attention on how the third- or fourth-order anharmonicity contributes to these physical quantities. Although it may be believed that the fourth-order anharmonicity should dominantly contribute to the fourth-order EXAFS cumulant through the first-order quantum statistical perturbation theory, it is consequently found that the experimental fourth-order EXAFS cumulant observed in fcc Ni, Cu, and stainless steel 316 are described mainly by the third-order anharmonicity through the second-order perturbation. In case of the elastic constants, such a situation is more prominent, and the contribution of the fourth-order anharmonicity is negligibly small for the estimation of temperature dependence of the elastic constants. We have also observed significant lattice strains on Cr and Mo in stainless steel 316 through the Fe, Ni, Cr, and Mo K-edge EXAFS measurements: a compressive lattice strain on Cr associated with larger thermal fluctuations and a more significant compressive lattice strain on Mo without enhanced thermal fluctuation. Such a characteristic dissimilarity may be caused by the differences in the atomic weights and the cohesive energies between Cr and Mo. Moreover, we have performed path-integral effective classical potential and classical Monte-Carlo simulations to describe the bulk moduli of the Invar and Elinvar alloys that show noticeable anomalies due to the so-called Invar effect. Appropriate temperature dependence of the bulk moduli is successfully obtained for the Invar, Elinvar, and stainless steel 304 and 316 alloys as well as elemental fcc Cu and Ni metals.

The Importance of Ligand-Induced Backdonation in the Stabilization of Square Planar d10 Nickel π-Complexes.

The electronic nature of Ni π-complexes is underexplored even though these complexes have been widely postulated as intermediates in organometallic chemistry. Herein, the geometric and electronic structure of a series of nickel π-complexes, Ni(dtbpe)(X) (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane; X=alkene or carbonyl containing π-ligands), is probed using a combination of 31 P NMR, Ni K-edge XAS, Ni Kβ XES, and DFT calculations. These complexes are best described as square planar d10 complexes with π-backbonding acting as the dominant contributor to M-L bonding to the π-ligand. The degree of backbonding correlates with 2 JPP from NMR and the energy of the Ni 1s→4pz pre-edge in the Ni K-edge XAS data, and is determined by the energy of the π*ip ligand acceptor orbital. Thus, unactivated olefinic ligands tend to be poor π-acids whereas ketones, aldehydes, and esters allow for greater backbonding. However, backbonding is still significant even in cases in which metal contributions are minor. In such cases, backbonding is dominated by charge donation from the diphosphine, which allows for strong backdonation, although the metal centre retains a formal d10 electronic configuration. This ligand-induced backbonding can be formally described as a 3-centre-4-electron (3c-4e) interaction, in which the nickel centre mediates charge transfer from the phosphine σ-donors to the π*ip ligand acceptor orbital. The implications of this bonding motif are described with respect to both structure and reactivity.

Degradation Mechanism of Ni-Rich Layered Cathode Materials during High Voltage Cycling Revealed By Multi-Model Synchrotron X-Ray Imaging and Spectroscopy Techniques

Ni-rich layered cathode materials are important candidates for lithium-ion batteries used for high energy density applications, such as electric vehicles. However, these materials are suffering severe capacity fade caused by surface reconstruction, unstable cathode-electrolyte interface (CEI) formation and micro crack formation during cycling, especially when a high cut off charge voltage is applied (such as 4.6 and 4.8V). To understand the origin of this capacity fade, state-of-the-art diagnostic tools are applied to understand their structure, chemical and morphological properties of LiNi0.94Co0.06O2 (NC) and LiNi0.92Co0.06Al0.02O2 (NCA) cathode materials during cycling. Electrochemical measurement results show that the NCA cathode delivered higher capacity and stable cyclic performance even cycled at a high cut of voltage of 4.8V. In situ X-ray absorption spectroscopy (XAS) results of NC and NCA electrodes measured during the first and 51st charge/discharge cycling between the voltage range of 2.8-4.4V showed that both Ni and Co contribute to the capacity by going through the Ni3+/Ni4+ and Co3+/Co4+ redox couples. The Ni-K edge XAS spectra of NC cathode charged to 4.8V showed slightly reduction of Ni4+ during the high voltage charging. While, XAS spectra of NCA cathode did not showed reduction of Ni4+ when the cell charged to the higher voltage. More interestingly, C, F, O, Ni and Co soft XAS spectroscopy of NC and NCA electrodes at the different state of charge provided more comprehensive insight into surface and bulk chemical properties. The results showed that much thicker CEI layer formed on the NC surface compared with the NCA cathode, indicated that Al-doping effectively reduced the side reaction of cathode materials with the electrolyte. We have also compared the morphological and chemical evolution of NC and NCA secondary particles using full-filed in-situ transmission X-ray microscopy (TXM) during the initial cycle. Results will be presented at the meeting. Acknowledgement This project was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies through Advanced Battery Material Research (BMR) program (Battery500 consortium) under Contract No. DESC0012704.

Promotional effect of Ga for Ni2P catalyst on hydrodesulfurization of 4,6-DMDBT

Ni2P catalysts supported on SiO2 and Ga-SiO2 were prepared by incipient wetness impregnation technique, and the effect of the electronic properties of Ni2P on hydrodesulfurization (HDS) performance was studied. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and in situ FT-IR with CO adsorption studies were used to examine structural and electronic properties of the supported Ni2P catalysts. The catalytic activity in hydrodesulfurization (HDS) was measured at 3.0 MPa and at three different temperatures of 613, 628, and 643 K in a three-phase fixed bed reactor using a model feed containing 500 ppm S as 4,6-DMDBT, 6000 ppm S as DMDS, 100 ppm N as quinoline, 1 wt% tetralin, and 0.5 wt% n-nonane in n-tridecane balance. In both cases, the HDS conversion was very high over 90%. For the product distributions, the Ni2P/SiO2 maintained a low direct desulfurization (DDS) selectivity at 26.5%, while the Ni2P/Ga-SiO2 exhibited higher DDS selectivity of 32.1% at 643 K. The Ni K-edge XANES and CO-adsorbed FT-IR analysis confirmed the electron enriched property of Ni2P on SiO2, but with the electron deficiency of Ni2P phase supported on Ga-SiO2 support. These results thus suggest that the electron deficient Ni2P favors σ-bonding with S compounds to promote direct desulfurization of 4.6-DMDBT.

Synchrotron X-ray absorption spectroscopy and cation distribution studies of NiAl2O4, CuAl2O4, and ZnAl2O4 nanoparticles synthesized by sol-gel auto combustion method

An array of modern approaches to X-ray including X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) were employed to examine the local atomic structure, cation distribution, and degree of inversion of nanocrystalline metal aluminate MAl2O4 (M = Ni, Cu, Zn) powders produced using the sol-gel auto combustion technique. All samples were revealed to display single-phase cubic spinel structure with Fd-3m space group, as established by the XRD results. The cation distribution within these aluminate spinel structures were completely unique as suggested by the divergent disparity in comparative intensity between (220), (400), (422), and (440) diffraction plans for each XRD pattern. Rietveld refinement examination of the XRD data validates the ZnAl2O4 samples as having normal spinel structure, while CuAl2O4 and NiAl2O4 samples comprise partially-inverse spinel structures with low and high degree of inversion, respectively. The investigative findings gained from experimental Ni, Cu, Zn, and Al K-edge XANES spectra accommodated with the hypothetical computation of absorption spectra using the FEFF9.7 code reinforce this. Four-fold synchronization with oxygen atoms was demonstrated by all Zn ions discovered in the ZnAl2O4 samples. Conversely, the Ni and Cu ions located in the NiAl2O4 and CuAl2O4 samples tend to be synchronized in both tetrahedral and octahedral fashion by four or six oxygen atoms, respectively. Additionally, M2+ altering from Zn2+ ions to be Cu2+ and Ni2+ ions caused a substantial translocation of divalent metal (M2+) ions from the tetrahedral (A) sites to octahedral (B) sites, as clearly demonstrated by the EXAFS spectra. Specifically, the degree of inversion in these metal aluminates is completely dissimilar and identified as 0.83 for NiAl2O4, 0.42 for CuAl2O4 and 0 for ZnAl2O4, as indicated by the curve-fitting analysis of Ni, Cu, and Zn K-edge EXAFS spectra. These values comprise vital data for comprehension of numerous pertinent properties.

First principles modeling of the structural, electronic, and vibrational properties of Ni40Pd40P20 bulk metallic glass

Abstract The structural, vibrational, and electronic properties of Ni40Pd40P20 bulk metallic glass have been studied using ab initio molecular-dynamics simulations and total-energy optimization. Structural analyses of the resulting ab initio models show the presence of a few to no P P bonds and two main building blocks, consisting of tricapped trigonal prism (TTP) and capped square anti-prism (CSAP) with P as the center of these blocks. The computed Pd and Ni K-edge spectra of extended X-ray absorption fine structure (EXAFS) are found to be in good agreement with experimental data. The configurational averaged static structure factor and the generalized vibrational density of states are also observed to be in good agreement with experimental data.

X-ray absorption near edge structure simulation of LiNi0.5Co0.2Mn0.3O2 via first-principles calculation.

Simulation of Ni K-edge X-ray absorption near edge structure (XANES) spectra in LiNi0.5Co0.2Mn0.3O2 (NCM523) was performed. The structure of NCM523 was optimized by first-principles calculation based on density functional theory and XANES spectrum simulation via the finite difference method. The calculated Ni K-edge XANES spectra of NCM523 with Li amounts of 1.0 and 0.5 showed good agreement with the measured spectra. The bond length between Ni and O shortened as the valence of Ni increased. Distortion of the structure resulting from Jahn–Teller distortion was observed with Ni3+. The XANES spectra of the Ni K-edge of Ni2+, Ni3+, and Ni4+ were calculated. In NCM523 with a Li amount of 1.0, the spectrum of Ni3+ shifts towards the higher energy side compared to that of Ni2+; at a Li amount of 0.5 the absorption edge of Ni2+, Ni3+, and Ni4+ shifts toward a higher energy as valence increases. Even at the same Ni valence number, the XANES spectra were different when the Li amounts were 1.0 and 0.5. Cation mixing of Li/Ni readily occurs at a Li amount of 1.0, more than that of 0.5 because of the super exchange interaction. The K-edge XANES spectrum of the Ni of the Li site did not change the position of the absorption edge of the Ni site Ni2+ XANES spectrum; a difference in shape of the shoulder peak and the pre-edge peak appeared. From these results, the Ni valence, bonding state, and cation mixing effect of Li/Ni on the Ni K-edge XANES spectrum in NCM523 were clarified.

Weathering processes and crystal chemistry of Ni-bearing minerals in saprock horizons of New Caledonia ophiolite

This paper proposes a detailed study of the formation of the main Ni ore that is today mined in the saprock horizon of New Caledonia ophiolite. More specifically, this study aims at, i) characterizing the nature and the crystal chemistry of the main Ni-bearing phases, and ii) better understanding the weathering processes that lead to such nickel enrichment in these horizons. The study focuses on a boulder (~20 cm in diameter) sampled in the saprock facies of the Koniambo massif, reflecting the early stages of peridotite bedrock weathering. This boulder is explored with a large panel of techniques, from the centimeter to the nanometer scale, including micro-imaging and X-ray absorption spectroscopy at the Ni and Fe K-edges. A characterization along the cross section reveals important heterogeneities in textures, and a large concentration of nickel in the outer part through an intense and connected Ni-phyllosilicate network that develop at the expense of the primary lizardite network. The inner part is preserved from the weathering by supergene fluids. Primary lizardite initially contains about 0.4 wt% NiO, similarly to surrounding olivine and pyroxene. In the outer part, the main Ni-bearing phases are identified as polygonal serpentine (up to ~5 wt% NiO) and two successive generations of talc-like minerals that contain ~20 to 36 wt% NiO. In these two minerals, nickel is very likely to form nano-clusters in the octahedral layers. The Fe3+/Fetotal ratios in serpentine minerals increases regularly from ~0.5 in primary lizardite, to ~0.95 in polygonal serpentine, traducing increasing local oxygen fugacity with increasing weathering degree.From molecular modeling, we propose that the large excess of water systematically observed for these Ni-rich minerals can be explained by nanometer sized crystals, which potentially require many additional hydrogen bonds (i.e., mainly silanol groups) to passivate crystal edges and preserve electro-neutrality. On the other hand, the main driving force leading to important nickel accumulation in the saprock horizon is likely to be the strong pH gradient present at all scales in the regolith profile, including at the boulder scale, which have major effects on the hydroxide solubility. As the pH decreases in the phyllosilicate network, we observe, i) the weathering and oxidation of the primary lizardite network, ii) the formation of a newly formed lizardite, iii) the formation of Ni-rich polygonal serpentine, iv) the formation of successive generations of Ni-rich talc-like minerals.

Nickel incorporation in perovskite-type metal oxides – Implications on reducibility

Nickel is often applied in heterogeneous catalysis for its high catalytic activity towards a large variety of reactions at affordable price. Nickel reduction from perovskite-type mixed oxides is increasingly exploited to generate active and stable Ni catalysts. To investigate implications of the host perovskite structure on Ni reducibility, Ni was incorporated on the B-site of three perovskite-type mixed metal oxides of different lattice symmetries (LaFeO3 – orthorhombic, LaCoO3 – rhombohedral and La0.3Sr0.55TiO3 – cubic). Structural parameters of the phase pure undoped and Ni-doped perovskites were determined using synchrotron X-ray diffraction (XRD) and Ni K-edge X-ray absorption spectroscopy (XAS). Rietveld refinement and extended X-ray absorption fine structure (EXAFS) data fitting were used to verify that at this substitution level Ni enters the B-site and adopts its coordination environment. Expansion of the unit cell was found in LaCoO3 and La0.3Sr0.55TiO3, whereas contraction was observed in the case of LaFeO3. X-ray absorption spectra showed that Ni-containing unit cells exhibit the same symmetry as the host perovskite-type mixed oxides. The mean oxidation state of Ni was found to be equal in all three cases irrespective of the host lattice (+2.5). Lattice symmetry had significant effect on lowering the Ni reduction temperature determined by hydrogen temperature programmed reduction and a correlation between reduction temperature and crystal tolerance factor was found.

Evidence for the Coordination–Insertion Mechanism of Ethene Dimerization at Nickel Cations Exchanged onto Beta Molecular Sieves

The mechanistic origin of alkene dimerization on Ni sites supported on aluminosilicates has been ascribed to both coordination–insertion (i.e., Cossee-Arlman) and metallacycle-based cycles; the latter is often invoked in the absence of externally supplied cocatalysts or activators that generate Ni-hydride or Ni-alkyl species to initiate coordination–insertion cycles. Determining the prevalent reaction mechanism at Ni sites is often complicated by the formation and consumption of alkene dimer products via oligomerization and other parallel reactions (e.g., cracking, isomerization) that occur at Bronsted acid sites on supports. Here, ethene dimerization (453 K) was studied on Beta zeolites synthesized to contain predominantly exchanged Ni2+ sites according to site balances determined by cation exchange, and to Ni structure determined by CO infrared, UV–visible, and Ni K-edge X-ray absorption spectroscopies. The catalytic behavior of Ni2+ sites was isolated by suppressing contributions from residual H+ sites...

Strain-Induced Stabilization of Charged State in Li-Rich Layered Transition-Metal Oxide for Lithium-Ion Batteries

Li-rich layered oxide (LLO) is a promising cathode material for lithium-ion batteries because of its large capacity in comparison with conventional layered rock-salt structure materials. In contrast to the conventional materials, it is known that LLO of 3d transition metal has a nanodomain microstructure; however, roles of each domain and effects of strain, induced by the microstructure, on electrode properties are still unclear. In this study, the influence of the strain on an electronic structure is studied to elucidate the stabilization mechanism of LLO material Li[Li0.2Ni0.2Mn0.6]O2 in the charged state by using resonant X-ray diffraction spectroscopy (RXDS), X-ray diffraction, and X-ray absorption spectroscopy (XAS) in combination with ab initio calculation. RXDS of a superlattice peak and XAS at Mn and Ni K-edges unveil that this material has a microstructure consisting of Mn-rich and Ni-rich domains, whose structures are similar to Li2MnO3 and LiNiO2, respectively. In the Ni-rich domain, trigonal d...

Structural Characterization of O3-Structure Layered Cathode Material for Rechargeable Sodium Ion Batteries

Sodium ion batteries (SIBs) have emerged as suitable alternative energy storage systems to Li ion batteries (LIBs) due to the cost-effective and ample Na source. Sodium layered oxides have considerable attention as cathodes for Na-ion batteries due to easy synthesis and simple structure. O3-type NaTMO2 materials, where single transition metal is an oxidizable element such as Cr, Mn, Fe, Co, Ni [1], have the capability to reversible intercalation reaction of Na ions [2,3], which is different from their Li analogues system, where only nickel and cobalt do reversible intercalation of Li ions [4]. Furthermore, various mixed transition metals can be realized in the TM layer to create new oxide compounds [5,6]. Among them, O3-NaNi1/3Fe1/3Mn1/3O2 shows a capacity around 130 mAh/g with good capacity retention when cycled to 4.0 V [7]. In this study, layered sodium-ion battery cathode material, O3-type NaNi1/3Fe1/3Mn1/3O2, was systematically investigated by using synchrotron-based x-ray techniques to characterize the detailed redox mechanism during electrochemical process and to understand the role of each transition metal structural behavior in the ternary-element material. In Figure 1, reversible changes in the Ni, Fe, and Mn K-edge X-ray Absorption Near Edge Structure (XANES) spectra show that reversible electronic structural changes in the local level during Na+ deintercalation/intercalation in the voltage range of 2.0 – 4.0 V. Moreover, Ni and Fe elements are both active in Na1–xNi1/3Fe1/3Mn1/3O2 cathode and redox couples of Ni2+/Ni3+/Ni4+ and Fe3+/Fe4+ are responsible for the charge compensation mechanism. High Resolution Powder Diffraction (HRPD) results reveal that O3-type (R-3m) phase transforms into a P3 (R3m) structure coupled with Na+/vacancy ordering during charge and further elucidate the final P3-OP2 of phase transformation on over-sodiated state. Furthermore, in the structure with the small quantity of sodium, internal Fe ion migration occurs from octahedral site into tetrahedral site, which is possible due to formed vacant space by highly deintercalation of Na ions and this atomic level of movement causes the layered structure to have structural distortions. An in-depth analysis of the structural behavior and reaction mechanism for NaNi1/3Fe1/3Mn1/3O2 cathode material when the Na ions are used of the entire composition widens an electrochemical perspective and suggests a direction where we better understand the nature of structure which can be used as the cathode for the advanced rechargeable batteries with high energy density. From these experimental results, we will discuss structural evolution behavior of layered NaNi1/3Fe1/3Mn­1/3O2 cathode material. More detailed results and discussion including reaction process of Ni, Fe, and Mn in the material will be presented in the AiMES 2018 meeting. Figure 1. XANES spectra of (a, b) Ni K-edge, (c,d) Fe K-edge, and (e,f) Mn K-edge during the 1st cycle of Na+ deintercalation/intercalation process. Reference s : [1] C. Delmas, C. Fouassier, P. Hagenmuller, Phys. B + C 99B (1980) 81–85. [2] S. Komaba, C. Takei, T.Nakayama,A.Ogata,N. Yabuuchi, Electrochem. Commun. 12 (2010) 355–358. [3] N. Yabuuchi, H. Yoshida, S. Komaba, Electrochemistry 80 (2012) 716. [4] S.P. Ong, V.L. Chevrier, G. Hautier, A. Jain, C. Moore, S. Kim, et al., Energy Environ. Sci. 4 (2011) [5] I. Saadoune, A. Maazaz, M. Menetrier, C. Delmas, J. Solid State Chem. 117 (1996) 111–117. [6] M. Sathiya, K. Hemalatha, K. Ramesha, J.-M. Tarascon, A.S. Prakash, Chem. Mater. 24 (2012) 1846–1853. [7] D. Kim, E. Lee, M. Slater, W. Q. Lu, S. Rood, C. S. Johnson, Electrochem. Commun. (2012), 18, 66. Figure 1

Beyond Conventional Reaction Mechanism of Ordered Mesoporous Nickel Oxide for Lithium Ion Batteries

In a recent days, as cutting-edge devices, such as cell phone, electric vehicle (EV) and energy storage system (ESS) become more sophisticated, the battery performance is required to be higher. As a result, metal oxides having a capacity several times larger than that of carbon have attracted attention as a candidate for a next-generation secondary battery. Although metal oxides show higher capacity than one of conventional theory, which is insertion, alloy and conversion reaction, but it has not been clearly determined. Nickel oxide (NiO) is very attractive anode material due to its chemically stable, cheap, environmentally benign, easy to synthesize properties, and high theoretical capacity (718 mAh/g). However, commercialization of NiO is hampered by its poor cycle performance and rate capability due to inherently severe volume changes during cycling. One of strategies to overcome these limitations is to synthesize nanostructured NiO with various morphology, such as nanofibers, nanowalls, hollow spheres, hierarchical structures, and especially porous structure. In this study ordered mesoporous NiO is synthesized by using KIT-6 as a hard template for the sake of higher performance. Low-angle X-ray diffraction (XRD) patterns of highly ordered mesoporous NiO is quite different from KIT-6 silica template. A new (110) peak appears before 2θ=1°, which indicates the meso-structure transformation from cubic to tetragonal or the lower space group after the silica template etching process. In wide angle XRD pattern, synthesized highly ordered mesoporous NiO is matched with cubic NiO (JCPDS 47-1049). N2 adsorption-desorption isotherms show that the obtained replicas possess high specific surface areas (92 m2/g), and large pore volumes (0.24 cm3/g). The SEM images prove their mesoporous structures, indicating that nanoreplication was uniformly performed without formation of other metal oxide phase. Its theoretical capacity is calculated through conversion reaction, in which NiO reacts with Li ion and is converted to metallic Ni nanoparticles and Li2O, but the conventional reaction mechanism cannot elucidate its high reversible capacity (~1000 mAh/g). So synchrotron radiation analyses are used to research detail mechanism study. Conventional reaction mechanisms in anode, such as insertion, conversion, and alloy, have respective consistency as shown in operando SAXS. Operando SAXS spectra of mesoporous NiO shows different behavior during 1st discharge compared to one of other anode materials, which follow conversion reaction. There are no significant changes of SAXS until ~1 mol of Li ion is reacted. Thereafter, the pore net volume changes increase and peak intensity decrease gradually indicating the loss of mesostructure upon the conversion reaction to form Ni and Li2O. These observation is similar to in situ XRD, which shows constant peak intensity until ~1 mol of Li ion is reacted and decrease because of phase transition from ordered mesoporous structure to amorphous phase, result of conversion reaction. In these results, retained peak intensity might be attributed to electrolyte participation reaction, not associated with the NiO lattice. For further study, ex situ XAS analysis is used to study the local atomic structure of cycled NiO in detail. Ni K-edge XANES spectra show negligible changes in initial stage of 1st discharge. These changes are also clearly observed in Ni K-edge EXAFS spectra, which show pristine and discharged to 200 mAh/g samples are similar and peak intensity of discharged to 400 mAh/g sample is lower. It indicates that electrolyte participation reaction (oligomer layer formation) takes place first, and then the conversion reaction occurs. In the middle stage of 1st discharge, it goes to metallic Ni, product of conversion reaction. The amplitudes of Ni-O and Ni-Ni peaks in mesoporous NiO decrease significantly and the amplitudes of Ni-Ni peak in metallic Ni increase with the increase of depth of the discharge due to displacement of reacting species during conversion reaction. There are no significant changes due to SEI layer formation in final stage of 1st discharge. Note that little changes of Ni K-edge XANES spectra are observed until charged to 600 mAh/g sample, and it goes to NiO-like phase till fully charged state in the 1st charge. It indicates that reversible conversion reaction takes only some part of entire reversible capacity, and the reversible oligomer formation / decomposition attributes to the remained reversible capacity. A similar consistency is shown on 2nd discharge. The XPS and HRTEM experiments were carried out for research of the electrolyte participation reaction. More details will be discussed in the meeting.