37 research outputs found
New mixed 3d cation fluorinated materials as positives electrodes for lithium-ions batteries : elaboration, structural characterization and electrochemical properties
Ce travail concerne lâapplication d'une stratĂ©gie de synthĂšse en deux Ă©tapes pour prĂ©parer de nouveaux matĂ©riaux fluorĂ©s Ă base de fer dans lâobjectif de les tester en tant que composĂ© actif dâĂ©lectrodes positives pour batteries Ă ions lithium : Ă©laboration dâun prĂ©curseur suivie dâun traitement thermique adĂ©quat. LâĂ©tude porte dans un premier temps sur les fluorures hydratĂ©s 3D Ă valence mixte de fer, Fe2F5(H2O)2 de structure weberite inverse et Fe3F8(H2O)2. Par traitement thermique sous air, deux hydroxyfluorures sont stabilisĂ©s, FeF2.5(OH)0.5 de structure pyrochlore et FeF2.66(OH)0.34 de structure HTB respectivement. LâĂ©tude de leur comportement Ă©lectrochimique montre dâexcellentes capacitĂ©s â 170 mAh.g-1 (2-4 V). Afin dâĂ©tudier l'impact de la nature des cations 3d sur les performances, les hydrates Ă©quivalents Ă cations mixtes, M2+Fe3+F5(H2O)2 (M = Mn, Ni) et M2+M3+2F8(H2O)2 (M2+ = Mn, Fe, Co, Ni, Cu ; M3+ = V, Fe), ont Ă©tĂ© synthĂ©tisĂ©s en milieu solvothermal dans une seconde partie. Des intermĂ©diaires amorphes oxyfluorĂ©s apparaissent lors de la dĂ©gradation thermique sous air avec en particulier CuFe2F6O, obtenu Ă partir de CuFe2F8(H2O)2, qui prĂ©sente une capacitĂ© remarquable de 310 mAh.g-1 (2-4 V). Enfin, des fluorures dâammonium Ă cations mixtes NH4M2+Fe3+F6 (M = Mn, Co, Ni, Cu), obtenus par mĂ©canosynthĂšse et la voie solvothermale, ont conduit aux premiers fluorures Ă cations mixtes trivalents M0.5Fe0.5F3 (M = Mn, Co, Ni, Cu) de structure pyrochlore par oxydation topotactique sous fluor molĂ©culaire F2 en tempĂ©rature.This work presents an innovative synthetic strategy to develop new fluorinated iron-based materials as positive electrodes for Li-ion batteries. This two-step elaboration method consists in the preparation of fluorinated precursors followed by an appropriate thermal treatment. The study initially focuses on tridimensional mixed valence iron fluorides, Fe2F5(H2O)2 with the inverse weberitestructural type and Fe3F8(H2O)2. The calcination under air leads to the formation of two new hydroxyfluorides, FeF2.5(OH)0.5 and FeF2.66(OH)0.34 with pyrochlore and HTB structural types respectively which present excellent electrochemical capacities â 170 mAh.g-1 (2-4 V). In a second part, the 3d-cation effect on oxyfluorides performances is evaluated from equivalent mixed metal cation hydrates, M2+Fe3+F5(H2O)2 (M = Mn, Ni) and M2+M3+2F8(H2O)2 (M2+ = Mn, Fe, Co, Ni, Cu, M3+ = V, Fe), synthesized solvothermally. Their thermal degradation under air reveals amorphous oxyfluorinated intermediates and among them, CuFe2F6O, obtained from CuFe2F8(H2O)2, with an remarkable capacity of 310 mAh.g-1 (2-4 V). In the last part, mixed ammonium fluorides (NH4)M2+Fe3+F6 (M = Mn, Co, Ni, Cu) are synthesized using mechanochemical and solvothermal routes. Their thermal topotactic oxidation under molecular fluorine F2 leads to the first trivalent mixed-cation fluorides M0.5Fe0.5F3 (M = Mn, Co, Ni, Cu) with pyrochlore typestructure
Nouveaux matériaux fluorés d'électrodes positives à cations 3d mixtes pour batteries à ions lithium : élaboration, caractérisation structurale et propriétés électrochimiques
This work presents an innovative synthetic strategy to develop new fluorinated iron-based materials as positive electrodes for Li-ion batteries. This two-step elaboration method consists in the preparation of fluorinated precursors followed by an appropriate thermal treatment. The study initially focuses on tridimensional mixed valence iron fluorides, Fe2F5(H2O)2 with the inverse weberitestructural type and Fe3F8(H2O)2. The calcination under air leads to the formation of two new hydroxyfluorides, FeF2.5(OH)0.5 and FeF2.66(OH)0.34 with pyrochlore and HTB structural types respectively which present excellent electrochemical capacities â 170 mAh.g-1 (2-4 V). In a second part, the 3d-cation effect on oxyfluorides performances is evaluated from equivalent mixed metal cation hydrates, M2+Fe3+F5(H2O)2 (M = Mn, Ni) and M2+M3+2F8(H2O)2 (M2+ = Mn, Fe, Co, Ni, Cu, M3+ = V, Fe), synthesized solvothermally. Their thermal degradation under air reveals amorphous oxyfluorinated intermediates and among them, CuFe2F6O, obtained from CuFe2F8(H2O)2, with an remarkable capacity of 310 mAh.g-1 (2-4 V). In the last part, mixed ammonium fluorides (NH4)M2+Fe3+F6 (M = Mn, Co, Ni, Cu) are synthesized using mechanochemical and solvothermal routes. Their thermal topotactic oxidation under molecular fluorine F2 leads to the first trivalent mixed-cation fluorides M0.5Fe0.5F3 (M = Mn, Co, Ni, Cu) with pyrochlore typestructure.Ce travail concerne lâapplication d'une stratĂ©gie de synthĂšse en deux Ă©tapes pour prĂ©parer de nouveaux matĂ©riaux fluorĂ©s Ă base de fer dans lâobjectif de les tester en tant que composĂ© actif dâĂ©lectrodes positives pour batteries Ă ions lithium : Ă©laboration dâun prĂ©curseur suivie dâun traitement thermique adĂ©quat. LâĂ©tude porte dans un premier temps sur les fluorures hydratĂ©s 3D Ă valence mixte de fer, Fe2F5(H2O)2 de structure weberite inverse et Fe3F8(H2O)2. Par traitement thermique sous air, deux hydroxyfluorures sont stabilisĂ©s, FeF2.5(OH)0.5 de structure pyrochlore et FeF2.66(OH)0.34 de structure HTB respectivement. LâĂ©tude de leur comportement Ă©lectrochimique montre dâexcellentes capacitĂ©s â 170 mAh.g-1 (2-4 V). Afin dâĂ©tudier l'impact de la nature des cations 3d sur les performances, les hydrates Ă©quivalents Ă cations mixtes, M2+Fe3+F5(H2O)2 (M = Mn, Ni) et M2+M3+2F8(H2O)2 (M2+ = Mn, Fe, Co, Ni, Cu ; M3+ = V, Fe), ont Ă©tĂ© synthĂ©tisĂ©s en milieu solvothermal dans une seconde partie. Des intermĂ©diaires amorphes oxyfluorĂ©s apparaissent lors de la dĂ©gradation thermique sous air avec en particulier CuFe2F6O, obtenu Ă partir de CuFe2F8(H2O)2, qui prĂ©sente une capacitĂ© remarquable de 310 mAh.g-1 (2-4 V). Enfin, des fluorures dâammonium Ă cations mixtes NH4M2+Fe3+F6 (M = Mn, Co, Ni, Cu), obtenus par mĂ©canosynthĂšse et la voie solvothermale, ont conduit aux premiers fluorures Ă cations mixtes trivalents M0.5Fe0.5F3 (M = Mn, Co, Ni, Cu) de structure pyrochlore par oxydation topotactique sous fluor molĂ©culaire F2 en tempĂ©rature
Fluorinated Materials as Positive Electrodes for Li- and Na-Ion Batteries
International audienc
Investigation of Amorphous Mixed-Metal (Oxy)Fluorides as a New Class of Water Oxidation Electrocatalysts
The development
of electrocatalysts for the oxygen evolution reaction (OER) is one of the principal
challenges in the area of renewable energy research. Within this context,
mixed-metal oxides have recently emerged as the highest performing OER
catalysts. Their structural and compositional modification to further boost
their activity is crucial to the wide-spread use of electrolysis technologies.
In this work, we investigated a series of mixed-metal F-containing materials as
OER catalysts to probe possible benefits of the high electronegativity of
fluoride ions. We found that crystalline
hydrated fluorides, CoFe2F8(H2O)2,
NiFe2F8(H2O)2, and amorphous
oxyfluorides, NiFe2F4.4O1.8 and CoFe2F6.6O0.7,
feature excellent activity and stability for the OER in alkaline
electrolyte. Subsequent electroanalytical and spectroscopic characterization
hinted that the electronic structure modulation conferred by the fluoride
ions aided their
reactivity. Finally, the best catalyst of the set, NiFe2F4.4O1.8,
was applied as anode in an electrolyzer comprised solely of earth-abundant
materials.</p
Les charpentes de Notre-Dame de Paris, questionnement du bois dans le patrimoine et premiers apports de lâĂ©tude des restes carbonisĂ©s
International audienc
Les charpentes de Notre-Dame de Paris, questionnement du bois dans le patrimoine et premiers apports de lâĂ©tude des restes carbonisĂ©s
International audienc
Investigation of mixed-metal (oxy)fluorides as a new class of water oxidation electrocatalysts
International audienc
Identification and optical features of the Pb<sub>4</sub>Ln<sub>2</sub>O<sub>7</sub> series (Ln = La, Gd, Sm, Nd); genuine 2D-van der Waals oxides
We report on the identification and survey of the Pb4Ln2O7 series (Ln = La, Gd, Sm and Nd) which turn out to be real van der Waals 2D oxides. In the neutral layers, strong covalent PbâO bonds together with external stereoactive Pb2+ lone pairs, which act as sensitizers, lead to an ideal matrix for enhanced and tunable luminescence by lanthanide emitters, tested here for Sm3+ and Eu3+ doping. DFT calculations and preliminary ex-solution experiments validate the weak bonding between the layers separated by 3.5 Ă
and suggest a indirect to direct crossover realized by isolating the layers
Influence of nitrogen constraint on quantitative resistance to clubroot in Brassica napus
International audienc
Naming, relocating and dating the woods of Notre-Dame âforestâ, first results based on collated data and archaeological surveys of the remains
International audienc