[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] 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.

[en] Hybrid supercapacitors, which combine a capacitive negative electrode and a faradaic positive electrode operating in an aqueous media, have many potential applications such as frequency regulation on the electrical grid, in particular when used in conjunction with intermittent energy sources. The purpose of this work is to study alternative designs to the aforementioned hybrid devices, by using composite materials which combine faradaic and capacitive contributions in the same electrode in order to maximize both energy and power densities. Cu₂O:graphene composite materials have been synthesized using a simple precipitation technique in order to improve the energy of capacitive graphene-based negative electrode materials. Cuprous oxide (Cu₂O) has been chosen due to its high theoretical capacity of 375 mAh.g⁻¹ associated with an active electrochemical window in the range −0.85 V to −0.20 V vs Hg/HgO (1 M KOH), thus being a potential candidate to serve as a negative electrode to combine with the known carbon/Ni(OH)₂ positive electrode in internal hybridized cell. An interesting initial capacity of more than 275 mAh g⁻¹ has been obtained for the Cu₂O:graphene composite material when cycled in a 6 M KOH solution at 0.1 mV s⁻¹, despite a progressive fading of the specific capacity upon cycling.

[en] Polycrystalline samples of (1-x) CeO₂-x/2 Bi₂O₃ phases, where x is the atom fraction of bismuth have been synthesized by the precipitation process and after the thermal treatment at 600 ^oC, under air. Samples are first characterized by the X-ray diffraction and scanning electron microscopy. To determine the samples specific surface areas, Brunauer-Emmett-Teller (BET) analyses have been performed. In the composition range 0≤x≤0.20, a cubic solid solution with fluorite structure is obtained. For compositions x comprised between 0.30 and 0.90, two types of T' (or β') and T (or β) tetragonal phases, similar to the well-known β' or β Bi₂O₃ metastable structural varieties, are observed. However, the crystal cell volumes of these β' or β Bi₂O₃ phases increase with the composition x in bismuth: this might be due to the presence of defects or substitution by cerium atoms, in the tetragonal lattices. Using X-ray diffraction profile analyses, correlations between bismuth composition x and crystal sizes or lattice distortions have been established. The solid-gas interactions between these polycrystalline materials and air-CH₄ and air-CO flows have been studied as a function of temperature and composition x, using Fourier transform infrared (FTIR) analyses of the conversions of CH₄ and CO gases into the CO₂ gas. The transformations of CH₄ and CO molecules as a function of time and temperature are determined through the intensities of FTIR CO₂ absorption bands. Using the specific surface areas determined from BET analyses, these FTIR intensities have been normalized and compared. For all bismuth compositions, a low catalytic reactivity is observed with air-CH₄ gas flows, while, for the highest bismuth compositions, a high catalytic reactivity is observed with air-CO gas flows. -- Graphical abstract: Catalytic efficiencies of CeO₂-Bi₂O₃system: catalytic actions on methane (on the left) or carbon monoxide (on the right) of (1-x)CeO₂-x/2 Bi₂O₃ samples, as a function of the fraction x, and for fixed temperatures: on the vertical axis, the intensities of CO₂ FTIR absorption bands are reported. Strong efficiency of bismuth rich samples for CO conversion. Display Omitted Research highlights: → Stabilization of metastable polymorph Bi₂O₃ phases in the mix system [(1-x)CeO₂+(x/2)Bi₂O₃] at 600 ^oC. → Solid gas interactions between this system and air-CO or air-CH₄ gas flows at various temperatures and bismuth compositions. → High efficiency of bismuth rich samples to convert CO into CO₂.