Structural modifications and electrochemical behaviour of the beta(II)-Ni(OH)(2)/beta(III)-NiOOH redox couple upon galvanostatic charging/discharging cycling

International audienceAmong the various crystallographic phases of nickel hydroxide, the β-form is the most widely used as the active mass of the positive electrode of nickel-based secondary cells. However, the exact electrochemical and structural behaviour of the redox system upon cycling and ageing remains to be clarified. This work reports the electrochemical behaviour under galvanostatic conditions of two non-doped Ni(OH)(2) samples having different initial crystallography and morphology. The evolution of these features is investigated as a function of the cycling conditions and more particularly as a function of the reduction state achieved on discharge. Electrodes cycled at the 1st discharge plateau show that charged/discharged active materials are very similar. However, when discharge is continued down to the so-called 'second discharge plateau', drastic changes are observed as an increase of the crystallisation degree and of the compactness of the Ni(OH)(2) powder. Some insights into the nickel electrode redox behaviour are given. It appears that the nickel electrode operates, upon charge, as a single-phase or as a mixed-phase system depending on the depth of discharg

Caractérisations physico-chimiques et électrochimiques d'hydroxydes de nickel synthétisés par électrodialyse

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Electrochemical behaviour of the β(II)-Ni(OH)2/β(III)-NiOOH redox couple upon potentiodynamic cycling conditions

International audienceThe electrochemical behaviour of pure and Co-doped Ni(OH)2 powders is investigated under potentiodynamic cycling conditions. Evolution of some β-Ni(OH)2 physical properties as a function of the oxidation state is followed by ex situ Surface Enhanced μ-Raman Spectroscopy and in situ Ellipsometry. Effects related to the first and second reduction steps, as well as to the sweeping rate, are qualitatively studied. When compared to the results that have been recently obtained under galvanostatic conditions [S. Deabate, F. Henn, Electrochim. Acta 50 (2005) 2823], the present work confirms that the second reduction process is strongly associated to the occurrence of a reduced phase, i.e. NiO2H2−var epsilon, with 0 < var epsilon < not, vert, similar0.3, at the surface of the active mass grains. This reduced phase exhibits spectroscopic features very similar to the initial hydroxide which is known to be highly insulating in regards to both electrons and protons transfer

Fracture of the radial sesamoid bone of the thumb: an unusual fracture

【Abstract】The hand consists of five sesamoids. Two of them are present at the metacarpophalangeal (MCP) joint of the thumb. Fracture of the sesamoid bones of the thumb is a rare injury and the literature on the radial side is seldom reported. We reported a case of a patient with a fracture of the radial sesamoid at the MCP joint of the thumb in order to increase attention regarding this type of injuries. A 44-year-old male, high level gymnastic trainer, was helping one of his athletes during an exercise while he reported a hyperextension trauma to the MCP joint of the right thumb. One week after trauma, he presented to the hand surgeon complaining of a painful thumb at the MCP joint level on its palmar aspect. Standard A-P and lateral X-rays revealed a fracture of the radial sesamoid and the fracture was treated with a splint for 3 weeks. He was able to resumed his entire work 6 weeks after the injury. The sesamoid fractures is an indicator of the magnitude of the hyperextension injury and sometimes associated with tears of the volar plate ligament of the MCP joint. And a failure to recognize the ligament injury may lead to a long-term hyperextension instability on pinching. Key words: Fracture, bone; Sesamoid bones; Thum

3 In situ and operando determination of the water content distribution in proton conducting membranes for fuel cells: a critical review

International audienc

Operando μ-Raman Measurement of Water Distribution Along and Across the Membrane in a Fuel Cell

International audienceTo obtain a fundamental understanding of the transport regimes governing the electrochemical behavior of the polymer electrolyte membrane fuel cell, the measurement of the membrane water content, along both directions parallel and perpendicular to the surface, is essential. In this paper, operando μ -Raman spectroscopy is used to probe the water content of the Nafion® membrane in the fuel cell (OCV around 1 V) working at constant stoichiometry and low relative humidity (20%). Water concentration profiles crossing the membrane thickness are obtained with μ m resolution at different locations of the active surface: at the middle and close to the inlets/outlets of the reactants, at the feed gas channel and under-lands areas. The influence of the operating temperature and of the current density delivered by the cell are investigated. Of particular interest for perspective fuel cells, the membrane inner water partition appears highly heterogeneous when operating at ambient conditions, and dependent on the delivered current. The increase of temperature decreases the membrane water content at all the probed positions and induces a less uneven water distribution. The membrane hydration appears to be a key parameter for understanding the water redistribution between cathode and anode with the change of the cell operating conditions

Solvent–Diluent Interaction-Mediated Solvation Structure of Localized High-Concentration Electrolytes

International audienceThe latest developments of localized high-concentration electrolytes (LHCEs) shed light on stabilizing the high-energy-density lithium (Li) metal batteries. It is generally considered that the nonsolvating diluents introduced into the LHCEs improve the viscosity and wettability of high-concentration electrolytes (HCEs) without changing their inner solvation structures, thus maintaining the highly coordinated contact ion pairs (CIPs) and ionic aggregates (AGGs) of the precursor HCEs with limited free solvent numbers and high Coulombic efficiency (CE) of Li metal anodes. Herein, we show an unexpected effect of the diluent amount on the solvation structures of the LHCEs: as the diluent amount increases, the proportions of free solvent molecules and CIPs rise up simultaneously. The latter is probably due to the partial splits of the AGGs via the dipole–dipole interactions between the diluent and solvent molecules. Accordingly, a moderately diluted LHCE shows the best Coulombic efficiency of Li metal anodes (99.6%), compared with the precursor HCE (97.4%) or highly diluted LHCE (99.0%). This work reveals a new criterion of the LHCE chemical formulation for the designing of advanced electrolytes for high-energy-density batteries

Original synthesis and spectroscopic study of thiophene triazine derivatives with enhanced luminescence properties

International audienc

Artificial nucleation sites with stable SEI for Li metal anodes by aggressive Al pulverization

Uneven nucleation and fragile solid electrolyte interphase (SEI) restrict the practical application of lithium (Li) metal anode. A versatile strategy to simultaneously overcome these two drawbacks is critical for Li metal batteries (LMBs). Herein we propose an "aggressive aluminum (Al) pulverization" strategy to form abundant artificial nucleation sites and robust SEI films adjacently, leading to homogeneous Li deposition/stripping and high Li Coulombic efficiency. A core-shell structure with Al core and alumina-silica (Al2O3-SiO2) shell, Al@Al2O3-SiO2 (AAS), could be easily synthesized, by modulating the chemical diffusion of silicon (Si) element towards Si-Al alloy surface. The active SiO2 sites not only contribute to form the robust SEI layer, but also facility the lithiation of the AAS, accelerating the conversion of reversible Li-Al alloy into inert Li3Al2 phase. The as generated AAS with Li3Al2 and Li12Si7 phases possess negligible Li nucleation over-potential (similar to 0.7 mV), serving as an optimal structure for dendrite-free Li plating/stripping with a prolonged life-span of 6 times longer than that of the unprotected counterpart in carbonate electrolytes

Characterization of Unusually Large “Pseudo-Single Crystal” of β-Nickel Hydroxide

International audienc