[en] The effect of various parameters on the yield for the electrochemical generation of ferrate was investigated for pressed pellet iron electrodes. An optimum yield was observed for a NaOH concentration of 14-16 M of the anolyte. The rate of iron dissolution and generation of ferrate increased when the temperature of the electrochemical cell is raised from room temperature to 50 deg. C. The pressure applied to the iron powder during the formation of the pellet electrode did not have a strong influence on ferrate generation, at least in the range investigated in this work (5-8 ton/cm²). On the other hand, the purity, particle size and packing density of the powders are important factors in determining the current yield for ferrate generation and the maximum yield was not obtained with the smallest particles investigated (<10 μm). An optimum yield for ferrate generation of 60% was observed for a 2 h electrolysis. The surface of the pressed pellet iron electrode was also analyzed following the electrolysis in 14 M NaOH by X-ray diffraction and X-ray photoelectron spectroscopies. The electrogenerated ferrate was not detected at the electrode surface but the presence of various iron oxides and sodium carbonate was evidenced by these techniques

[en] This huge publication gathers interventions and contributions of a colloquium which notably addressed the following issues: bio-energies, hydrogen and fuel cells, energy storage, photovoltaic solar energy, energy efficiency in buildings, transports and industry, CO_2 capture and storage. On the first day, after two interventions on Energies Programmes at the ANR and an overview of R and D world challenges regarding energy, the contributions addressed the above mentioned issues. During the next day, besides these issues, contributions addressed challenges for tomorrow's society and perspectives for research. Thematic sessions addressed bio-energies (optimized production of cellulose ethanol, the third generation, technological deadlocks for the thermal-chemical route), photovoltaic solar energy (new concepts, massive crystalline silicon and photovoltaic thin layers), high energy efficiency buildings, energetic equipment and climate engineering, CO_2 storage, CO_2 capture, fuel cells, hydrogen production, transport and storage, electrochemical and non-electrochemical storage of energy, transports (internal combustion engine and power units, electric transports)

[en] The reaction mechanism describing the formation and surface decomposition of Ni₃P has been investigated. Ni₃P was synthesized as a thick film on a Ni foil by a simple solid-state reaction. X-ray diffraction confirms that the layer produced, on the surface of the Ni foil, is pure Ni₃P. The solid-state reaction did not occur at 400 deg. C or lower temperatures. At 600 deg. C or higher temperatures the solid-state reaction occurred by a nucleation mechanism of synthesis and later sintering of Ni₃P particles at the surface of the Ni foil. The surface of the Ni₃P-Ni foil showed to be stable in air up to 300 deg. C. At higher temperatures, Ni₃P decomposed trough a complex mechanism, including the loss of phosphorus, the formation of the phases Ni₁₂P₅ and Ni₂P, and finally, oxidation of the nickel phosphides. Samples heated at 800 deg. C for 4 h produced a NiO layer on the surface of the Ni₃P-Ni foil

[en] Copper phosphide (Cu₃P) was produced as thick films over copper foils. The synthesis was performed by solid-state reaction at low temperature (400 deg. C). Similar attempts were carried out for other transition metals of the first series without success. Scanning electron microscopy (SEM) revealed the formation mechanism of the Cu₃P thick films. First, phosphorus diffuses into the copper foil followed by the subsequent formation of the binary compound. During this process, the Cu₃P particles seem to dig the copper foil, producing holes, where the Cu₃P crystallites nucleate and growth. Then, the thick films are formed by the conjugation of several agglomerates and their morphology is not homogeneous. Oxidation of Cu₃P occurs to a small extend on the top surface of the films. The electrochemical behaviour of the thick film was compared with a standard Cu₃P composite electrode, in which the active material is mixed with carbon and a binder. Although the two different electrodes presented some differences in their electrochemical behaviour, both electrodes showed promising qualities to be used as anode materials in lithium ion batteries or hybrid devices

[en] Activated carbon products modified with benzoic, benzenesulfonic and benzylphosphonic acid groups were prepared by spontaneous reduction of aryldiazonium ions in situ generated in water from the corresponding aminobenzene organic acids without addition of an external acid. Electrochemistry and NMR studies show that the advancement of the diazotization reaction depends both on the acidity and the electronic effect of the organic acid substituent, giving a mixture of diazonium, amine and triazene functionalities. Carbon products prepared by reaction of activated carbon Norit with 4-aminobenzenecarboxylic acid, 4-aminobenzenesulfonic acid and (4-aminobenzyl)phosphonic acid were analyzed by chemical elemental analysis and X-ray photoelectron spectroscopy experiments. Results show that this strategy is well suited for the chemical functionalization, giving a maximized grafting yield due to a chemical cooperation of amine and diazonium functionalities

[en] In situ/in operando X-ray diffraction coupled with electrochemical cycling of ZnO based electrodes in KOH electrolyte has been used as a powerful tool in order to investigate the influence of additives. The technique has been performed in order to highlight the role of bismuth based conductive additives on the cycling ability of the electrode. It enables to clearly evidence the conversion of zinc oxide to zinc metal. During the first charge, it also helps to visualize the conversion of Bi₂O₃ additive into metallic bismuth prior to ZnO reduction which leads to the formation of an electronic pathway at the nanometer scale complementary from the current collector and the TiN percolation conductive network. Additionally, each Bi₂O₃ grain seems to be converted in a single bismuth grain which is not agglomerated with other bismuth particles even after 50 cycles. This behaviour leads to a steady capacity of the zinc based electrode compared to the same electrode without Bi₂O₃ additive. Subsequently, in situ XRD investigation of Zn based negative electrode in nickel–zinc batteries can be a powerful tool to design new composite electrode with long term cycling efficiency

[en] Highlights: • Two asymmetric devices are presented for the first time: C/BSCF and FeWO₄/BSCF. • These devices present a better self-discharge behavior than C/C device. • These devices present an excellent stability over 10,000 and 45,000 cycles, respectively. • C/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ has similar volumetric energy density as C/C. -- Abstract: Two asymmetric aqueous electrochemical capacitors operated in 5 M LiNO₃ are reported: C/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) and FeWO₄/BSCF, with activated carbon and FeWO₄ (synthesized by a precipitation method) as negative electrodes, respectively, and BSCF (synthesized by a modified glycine-nitrate process) as positive electrodes. These two devices were operated between 0 and 1.6 V and between 0 and 1.4 V, respectively. They demonstrated a remarkable cycling ability with a high capacitance retention over 10,000 and 45,000 cycles, respectively. Thanks to the high density of BSCF, the C/BSCF device exhibits a volumetric energy density up to 2.7 Wh L⁻¹ at low current densities. This study demonstrates the advantages and limits of the use of high density multicationic oxides with pseudocapacitive behavior to improve the volumetric energy density of aqueous electrochemical capacitors.

[en] Spontaneous grafting of chloroanthraquinone (ClAQ) groups on Black Pearls carbon by reduction of the corresponding in-situ generated diazonium cations was successfully achieved. The presence of an halogen atom on the quinone molecule allowed the use of different spectroscopic characterization techniques to determine the accurate quinone content of the modified carbon. Electrochemical characterization highlighted that the presence of chlorine atom on the grafted molecule did not affect the electrochemical response or the grafting reaction efficiency. The amount of ClAQ molecules at the carbon surface after grafting was determined by cyclic voltammetry, together with thermogravimetric analysis coupled mass spectroscopy, X-ray photoelectron spectroscopy and elemental analysis. The ClAQ mass loadings estimated from the four techniques are in very good agreement and confirm that the grafted moieties are all electrochemically active and accessible. Finally, the grafting of quinone-type molecule using the reduction of diazonium cations does not affect the electroactivity of the grafted groups and cyclic voltammetry can be considered as a reliable technique to evaluate the mass loading of grafted quinone groups on porous carbon. Thus ClAQ can be used as a grafted probe molecule to investigate grafting yield on carbon powder, and this approach can be extended to functionalized electrodes used in an increasing number of electrochemical energy storage devices.

[en] Lead dioxide thin films were electrodeposited on gold substrates and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mass change occurring upon immersion in a H₂SO₄ electrolyte and during electrochemical reduction was observed in situ by electrochemical quartz crystal microbalance (EQCM). A hydrated PbO₂ gel-type layer is formed at the surface of electrodeposited PbO₂. The concentration of the H₂SO₄ electrolyte does not affect the composition of the gel nor the amount of lead dioxide involved in the hydration process. It is established that 1.3 x 10^-7 mol cm^-2 of β-PbO₂ are hydrated at the surface of an electrodeposited film and that the hydration reaction occurs according to the following reaction: PbO₂^(crystal) + xH₂O ↔ (PbO(OH)₂.(x - 1)H₂O)^(gel), where x = 8.1. The mass change occurring during the first and subsequent discharge of PbO₂ was recorded. It is shown that both PbO₂^(crystal) and PbO(OH)₂.(7.1)H₂O)^(gel) are reduced to PbSO₄ during the first discharge.

[en] Ba_0.5Sr_0.5Co_xFe_1-xO_3-δ phases, with 0.75 < x < 0.90, so-called BSCFs, were investigated as pseudocapacitive electrode materials. These polycationic oxide phases were prepared by a modified glycine-nitrate process and show the same perovskite structural arrangement and similar morphological characteristics in the whole series. The electrochemical performance was evaluated in aqueous electrolytes at room temperature. BSCF powders showed promising pseudocapacitive behavior as electrode materials with high volumetric capacitances which depend on the Co/Fe ratio. A volumetric capacitance of 500 F cm⁻³, i.e. five times higher than that of a standard activated carbon electrode, was measured in 5.0 M LiNO₃ for the electrode based on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ material composition (x = 0.80). The electrode also exhibited moderate self-discharge and 90% of capacitance retention over 2000 cycles. The charge storage mechanism seems to be dependent upon the nature of the ions in the electrolyte and on the Co/Fe ratio.