Electrochemical Intercalation Of Oxygen Research Articles

Phase diagram and redox behaviour of (Nd/Pr)2NiO4+δ electrodes explored by in situ neutron powder diffraction during electrochemical oxygen intercalation

Phase diagram and redox behaviour of (Nd/Pr)₂NiO_4+δ electrodes explored by <i>in situ</i> neutron powder diffraction during electrochemical oxygen intercalation

(Nd/Pr)2NiO4+δ: Reaction Intermediates and Redox Behavior Explored by in Situ Neutron Powder Diffraction during Electrochemical Oxygen Intercalation.

Oxygen intercalation/deintercalation in Pr2NiO4+δ and Nd2NiO4+δ was followed by in situ neutron powder diffraction during electrochemical oxidation/reduction, in a dedicated reaction cell at room temperature. For both systems three phases, all showing the same line width, were identified. The starting phases Pr2NiO4.23 and Nd2NiO4.24, considered with an average orthorhombic Fmmm symmetry, although both show a slight monoclinic distortion, get reduced in a two-phase reaction step to tetragonal intermediate phases with 0.07 ≤ δ ≤ 0.10 and P42/ ncm space group, which on further reduction transform, again in a two-phase reaction step, toward the respective stoichiometric (Pr/Nd)2NiO4.0 phases, with Bmab space group. Electrochemical oxidation does, however, not proceed fully reversibly for both cases: while the reoxidation of Nd2NiO4+δ is limited to the tetragonal intermediate phase with δ = 0.10, the homologous Pr2NiO4+δ can be reoxidized up to δ = 0.17, showing orthorhombic symmetry. For the intermediate tetragonal phase, we were able to establish for Pr2NiO4.09 a complex anharmonic displacement behavior of the apical oxygen atoms, as analyzed by single-crystal neutron diffraction and maximum entropy analysis, in agreement with a low- T diffusion pathway for oxygen ions, activated by lattice dynamics.

Electrochemical oxygen intercalation into Sr2IrO4

Oxygen was electrochemically intercalated into Sr2IrO4 sintered samples, single crystals and a thin film. We estimate the diffusion length to a few μm and the concentration of the intercalated oxygen to δ≃ 0.01. The latter is thus much smaller than for the cuprate and nickelate parent compounds, for which δ > 0.1 is obtained, which could be a consequence of larger steric effects. The influence of the oxygen doping state on resistivity is small, indicating also a poor charge transfer to the conduction band. It is shown that electrochemical intercalation of oxygen may also contribute to doping, when gating thin films with ionic liquid in the presence of water.

Solid-state reactivity explored in situ by synchrotron radiation on single crystals of SrFeO2.5 during electrochemical oxygen intercalation

Solid-state reactivity explored in situ by synchrotron radiation on single crystals of SrFeO_2.5 during electrochemical oxygen intercalation

Solid-state reactivity explored in situ by synchrotron radiation on single crystals: from SrFeO2.5 to SrFeO3 via electrochemical oxygen intercalation**Dedicated in honour of Professor Robert SchÖllhorn on the occasion of his 80th birthday.

In this study we demonstrate the feasibility of following up a chemical reaction by single crystal x-ray (synchrotron) diffraction under operando conditions, carried out in a specially designed electrochemical cell mounted on the BM01A at the European Synchrotron Radiation Facility (ESRF). We investigated in detail the electrochemical oxidation of SrFeO2.5 to SrFeO3 on a spherical single crystal of 70 µm diameter by in situ diffraction at an ambient temperature. Complete data sets were obtained by scanning the whole reciprocal space using a 2M Pilatus detector, resulting in 3600 frames with a resolution of 0.1° per data set, each obtained in 18 min. The crystal was mounted in a specially designed electrochemical cell with 1N KOH used as the electrolyte. During the electrochemical oxidation, the reaction proceeds following the phase sequence SrFeO2.5/SrFeO2.75/SrFeO2.875/SrFeO3, structurally accompanied by establishing a complex series of long-range oxygen vacancy ordering, which gets instantly organized at ambient temperature. The topotactic reaction pathway is discussed in terms of the evolution of the twin domain structure. The formation of SrFeO2.875 is accompanied by the formation of diffuse streaks along the [1 0 0]-direction of the perovskite cell, reaching high d-spacings. The diffuse streaks are discussed and are thought to originate from a modified twin structure induced by the SrFeO2.75 to SrFeO2.875 transition, and the associated changes in the domain structure, developed during the oxygen intercalation. We equally analysed and discussed in detail the twin structure of all the title compounds. We confirm the ground state of SrFeO2.5 is able to adopt the Imma space group symmetry, showing stacking faults of the tetrahedral layers along the stacking axis of the brownmillerite unit cell, indicated by the 1D diffuse rods. We showed that in situ single crystal diffraction has huge potential in the study of non-stoichiometric compounds under operando conditions, in order to obtain structural information i.e. about diffuse scattering, and microstructural information related to domain effects such as twinning—information far beyond that which powder diffraction methods allow us to obtain.

Electrochemical Oxygen Intercalation into Perovskite-Derived Materials

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Electrocatalytic Behavior of Perovskite-Related Cobaltites and Nickelates in Alkaline Media

Dense ceramic anodes of perovskite-type La1-x-ySrxCo1-zAlzO3-δ ( x = 0.45-0.70; y = 0- 0.05; z = 0-0.20) and K2NiF4-type La2Ni1-xMexO4+δ (Me = Co, Cu; x = 0-0.20), synthesized by the glycine-nitrate technique, were assessed for oxygen evolution in alkaline media. The lowest overpotentials are observed for (La0.3Sr0.7)0.97CoO3-δ, which exhibits a significant oxygen deficiency in combination with high conductivity associated with the A-site cation nonstoichiometry compensation mechanism via Co4+ formation. Perovskite-type cobaltite anodes are essentially stable in alkaline solutions, whilst La2NiO4-based electrodes exhibit degradation at the potentials where the oxygen evolution occurs, probably due to the electrochemical oxygen intercalation in the lattice.

Room-Temperature Electrochemical Intercalation of Oxygen or Fluorine into La2CuO4 Using Organic Electrolytic Media: Mechanistic Approach

The electrochemical intercalation of oxygen into has been studied in various anhydrous organic media. Several combinations between an organic solvent and a supporting electrolyte have been examined. The addition of an oxygen source such as or has been found to be unnecessary. Experiments have shown that the electrochemical oxygen insertion mainly implies the decomposition of the solvent leading to the formation of oxygen species able to oxidize the starting material. has been prepared in the DMSO associated with A superconducting behavior is observed below 44 K and the physical characterizations of the material before and after controlled anodic polarization are reported. It has also been shown that this intercalation reaction is reversible. The mechanism of the oxygen intercalation is tentatively proposed with respect to the organic media. Fluorine has also been intercalated for the first time in such media. © 2004 The Electrochemical Society. All rights reserved.

Electrochemical oxidation of La2CuO4 in organic media: influence of the electrolyte composition

The electrochemical intercalation of oxygen into La2CuO4 has been carried out in various anhydrous organic media: a variety of combinations of dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and acetonitrile (AN) as solvents, NaClO4 or nBu4NBF4 as supporting electrolytes, and the presence or absence of oxygen sources (H2O, KO2) have been studied. The various experiments show that the intercalated oxygen comes mainly from the solvent (DMSO, DMF), which plays a major role, leading, via its decomposition, to the formation of oxygen species able to oxidise the material. Anodic polarisation performed at room temperature gives rise to interesting materials with compositions up to La2CuO4.10, for which superconducting behaviour is observed below 42 K. The physical characterisations of the material (XRD, chemical composition, electronic properties) before and after controlled anodic polarisation are reported. This “chimie douce”-type intercalation proves to be as efficient as that previously performed in alkaline solution.

Electrochemical topotactic oxidation of nonstoichiometric perovskites at ambient temperature

Different approaches to describe nonstoichiometry in perovskite-related oxides, oxygen diffusion models and kinetic data on electrochemical intercalation of oxygen in perovskite-related oxides are considered in the present study. It is demonstrated that the formation of microheterogeneous systems is characteristic of nonstoichiometric perovskite-related oxides. The adequate models should be considered for the proper characterization of the low temperature oxygen transport in oxides. These models should account for the high concentration of the high diffusivity paths in the sample. For microdomain textured Ca0.5Sr0.5FeO2.5 perovskite as example, the kinetic analysis of electrochemical oxygen intercalation is carried out.  2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Evidence of Oxygen Intercalation and Mobility at Room Temperature in Oxides: An Electrochemical Quartz Microbalance Study of Intercalation in La2CuO4

This paper offers direct evidence for the electrochemical intercalation of oxygen in an oxide with the K2NiF4 structure, namely, La2CuO4, at room temperature. Organic solvents, as well as water, allow that reaction to occur. The charge-to-mass ratio evaluated from a comparison with fluoride intercalation implies that either OH- or Oδ- species are being intercalated. Comparison with previous work seems to favor the latter. If an oxygen with lower charge is moving, that could indeed explain why oxygen conductivity can be observed at such low temperatures.

Electrochemical oxygen intercalation in La 2CuO 4 prepared by nitrates method: Microstructural effects

In order to determine microstructural effects in the electrochemical oxygen intercalation for La 2CuO 4, and the relative abundance of the two superconducting phases (T c = 33 and 44K), this oxide was prepared using the nitrates method, which involves the dissolution of La and Cu oxides in nitric acid. The product was pressed as pellets. A narrow grain size distribution and a density higher than 95% ϱ T was obtained. After electrochemical oxygen intercalation, at room temperature, this material gave a main superconducting phase with T c = 33K, whereas porous pellets obtaiined from the same oxide, with intermediate grinding, gave a T c = 44K.

Electrochemical intercalation of oxygen into La2CuO4 using anhydrous organic electrolytic media

The electrochemical intercalation of oxygen into La2CuO4 has been carried out for the first time in anhydrous organic–inorganic media such as dimethyl sulfoxide (DMSO)/0.1 M NaClO4 or nBu4NBF4. The electrochemical reaction needs the presence of an oxygen source (KO2) even with potential oxidising supporting electrolytes (NaClO4). The anodic polarisation is performed at room temperature, with the aim of replacing the usual efficient but sometimes aggressive alkaline media. This so-called chimie douce reaction gave rise to noteworthy materials having compositions up to La2CuO4.08 for which superconducting behaviour was observed below 42 K. The physical characteristics of the material (XRD, chemical composition, electronic properties) before and after controlled anodic polarisation are reported. The processes are time dependent and the oxygen stoichiometry could be controlled through reaction times.

Electrochemical Investigation of Oxygen Intercalation into La2CuO4+δPhases

In this work the electrochemical intercalation of oxygen in La2CuO4phases has been studied. Oxygen intercalation has been performed at different anodic potentials for fixed time in alkaline solution (1 M NaOH) at room temperature. The electrochemistry of the phenomena taking place at the oxide–solution interface has been investigated by cyclic voltammetry (CV), controlled-potential coulometry, and electrochemical impedance spectroscopy (EIS). The homogeneity of processed samples and the lattice parameters prior to and after oxygen intercalation have been verified by X-ray powder diffraction. SEM has been used to relate surface modification to the potential applied after electrochemical oxygen intercalation. The recent theories and knowledge of mechanisms of oxygen intercalation into the oxide lattice have been related to the experimental results. Oxygen intercalation seems to occur at potentials slightly lower than that of the oxygen evolution reaction (OER) and proceeds on a parallel pathway to O2evolution at more anodic potentials.

Mechanisms and Kinetics of Electrochemical Intercalation of Oxygen into Nd2NiO4+δ

ABSTRACTOverstoichiometric insertion of oxygen into thin films of Nd2NiO4+δwas performed electrochemically at room temperature (RT) in order to obtain an in-situ compositional analysis of the process. Thin Nd2NiO4+δlayers were deposited onto resonators of a Quartz Crystal Microbalance (QCM) by Pulsed Laser Deposition (PLD). Cyclic voltammograms showed oxidation and reduction peaks typical for these oxides. The change in oxygen stoichiometry was determined by in-situ QCM measurements during potential step experiments. The resulting maximum mass change was on the order of 50 ng and corresponded to a maximum excess oxygen content of δ = 0.12 in Nd2NiO4+δ. The time dependence of the mass change was described by a transport model which leads to oxygen diffusion coefficients in the range from 2.10−12 to 10−11 cm2/s depending on δ and the direction of the reaction.

Growth and electrochemical oxidation of MBE-grown c-axis La 2CuO 4 thin films on different substrates

The growth and subsequent electrochemical oxygen intercalation of c-axis La 2CuO 4 + δ thin films on substrates with different lattice mismatch [SrTiO 1 (001) (+3.03%), NdGaO 1 (001) (+1.90%). LaAlO 3 (001) (−0.05%) and SrLaAlO 4 (001) (−0.95%) substrates] are compared. The films grown on the different substrates can all be oxidized electrochemically, but their structural and transport properties differ vastly. The results can roughly be divided into two categories, i.e., those of films grown with a compressive or a tensile lattice mismatch where the former have a larger c-axis latice parameter and better transport properties.

Growth, microstructure, and electrochemical oxidation of MBE-grown c-axis La2CuO4 thin films.

The growth, microstructure, and electrochemical oxygen intercalation of c-axis ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4+\mathrm{\ensuremath{\delta}}}$ thin films on substrates with different lattice mismatch [${\mathrm{SrTiO}}_{3}$ (001) and ${\mathrm{SrLaAlO}}_{4}$ (001) substrates] are compared. Except for the absence of planar defects in the latter case, the microstructural properties of both film types are very similar. For films on ${\mathrm{SrTiO}}_{3}$, oxygen can be intercalated electrochemically into the grown c-axis thin film with a high diffusion coefficient (${\mathit{D}}_{\mathrm{ox}}$=${10}^{\mathrm{\ensuremath{-}}13}$--${10}^{\mathrm{\ensuremath{-}}14}$ ${\mathrm{cm}}^{2}$/s), and subsequently additional (00l) reflections, l=2n+1, are observed by x-ray diffraction measurements. A double transition with a resistivity drop at \ensuremath{\simeq}55-58 K, suggesting a more strongly oxidized phase, and a zero-resistance state at \ensuremath{\simeq}42 K are found. For films on ${\mathrm{SrLaAlO}}_{4}$, the value of ${\mathit{T}}_{\mathit{c}}$ could not be raised further, as the films decompose during the anodic polarization. This comparison reveals the role of planar defects, and we propose an electrochemical oxidation mechanism that occurs in two steps: First oxygen is transported into the film by intercalation into the planar defects, and then a slower oxygen diffusion into the interstitial sites occurs along the ab planes. \textcopyright{} 1996 The American Physical Society.

Electrochemical oxygen intercalation in La 2NiO 4 + δ crystals

The electrochemical intercalation of oxygen from an aqueous KOH electrolyte into La 2NiO 4 + δ has been investigated by a potential step method at potentials below oxygen evolution. The first reduction cycle occurs at nearly constant potential for the whole composition range and is characteristic of nucleation and growth behavior. On the first oxidation and subsequent reduction-oxidation cycles, the results are similar to those obtained previously for polycrystalline electrodes and show the presence of a two-phase region for 0 ≤ δ ≤ 0.06 and a single phase with the composition 0.06 ≤ δ ≤ 0.13. The P4 2 ncm phase with δ ∼ 0.02 and a narrow range of stoichiometry, is apparent in dδ dV versus δ data and in the behavior of the current decay curves. Examination of the crystals at various stages of cycling show the formation of extensive cracks that apparently increase in density with cycling. Measurements of the transient currents after potential steps have been used to estimate the diffusion coefficient of oxygen in La 2NiO 4 + δ in the single phase region. Data were obtained for both polycrystalline and single crystal electrodes.

Electrochemical synthesis: oxygen intercalation

The electrochemical intercalation of oxygen into oxide networks, observed for the first time in 1990, stimulated great interest in the field of solid state chemistry. Considered at first as a questionable process, many research groups now agree that the electrochemical reaction indeed leads to the insertion of oxygen species into the parent network. Potentiostatic as well as galvanostatic experiments carried out in alkaline solution have allowed chemists to prepare fully oxidized compounds such as SrMO 3 perovskites (MFe, Co) or overoxidized Ln 2MO 4+δ materials (MNi, Cu), some of them exhibiting peculiar physical properties. In spite of the large size of the oxygen anions, much similarity is found between oxygen intercalation and cationic intercalation.

Electrochemical intercalation of O 2− in La 2CuO 4 single crystals

The electrochemical intercalation of oxygen in La 2CuO 4 single crystals was studied using electron paramagnetic resonance and magnetic susceptibility measurements. Chronoamperometric experiments showed that, in the intercalation process, the O 2− diffusion in single crystals is extremely slow ( D ≈ 10 16cm 2s −1). This diffusion coefficient depends strongly on temperature and the enthalpy diffusion was found to be ca. 750 kJ deg −1 mol −1. Crystals under electro-oxidation for one to two weeks still show the presence of the antiferromagnetic and a superconducting phases. This was supported by the simultaneous observation of line splitting in the EPR spectra and superconducting diamagnetic signal.