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See detailA Mössbauer spectral study of degradation in La0.58Sr0.4Fe0.5Co0.5O3−x after long-term operation in solid oxide electrolysis cells
Mahmoud, Abdelfattah ULiege; Al Daroukh, Mahmoud; Lipinska-Chwalek, Marta et al

in Solid State Ionics (2017), 312

Degradation processes of oxygen electrodes in solid oxide electrolysis cells (SOECs) were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ... [more ▼]

Degradation processes of oxygen electrodes in solid oxide electrolysis cells (SOECs) were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Mössbauer spectroscopy. La0.58Sr0.4Fe0.5Co0.5O3−x (LSCF) anodes (oxygen electrode) were analyzed after different longterm operations durations of 1774, 6100 and 9000 h. The results were compared with a cell in the initial state. Besides the LSCF anode, the SOECs were composed of a Ce0.8Gd0.2O1.9 barrier layer between the anode and electrolyte, yttria-stabilized zirconia (YSZ) as electrolyte and Ni-YSZ as cathode (hydrogen electrode). Mössbauer spectra of the iron-containing anode were acquired in order to determine the alteration of the iron oxidation state and its local environment during operation. Mössbauer spectroscopy yields indirect information about the degradation mechanism, especially in combination with SEM, TEM, and XRD. XRD and TEM revealed the appearance of Co3O4 during the SOEC operation and SEM analyses confirmed the formation of SrZrO3 at the electrode/electrolyte interface. The spectral analysis confirmed the reduction of iron from Fe(IV) to Fe(III) in LSCF after long-term operation. The fraction of Fe(IV) in the electrode decreased with time and 18, 15, 13 and 11% were obtained for 0, 1774, 6100, and 9000 h of operation, respectively. [less ▲]

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See detailA SPRAY DRYING METHOD FOR THE PREPARATION OF Na2FePO4F/CB AND Na2FePO4F/CNT COMPOSITES CATHODE FOR LITHIUM-ION BATTERIES
Mahmoud, Abdelfattah ULiege; Berardo, Loris ULiege; Brisbois, Magali et al

Poster (2017, September 18)

Fluorophosphates are considered among the most interesting series of cathode material for Li/Na-ion batteries1. Na2FePO4F (space group Pbcn), with its layered structure and two-dimensional pathways for ... [more ▼]

Fluorophosphates are considered among the most interesting series of cathode material for Li/Na-ion batteries1. Na2FePO4F (space group Pbcn), with its layered structure and two-dimensional pathways for facile Na+/Li+ transport, exhibits minimal structural changes upon reduction/oxidation. The average working voltage is 3.3 V vs. Li/Li+. Intercalation/deintercalation results in a volume change of only 3.7%. However, one of the key drawbacks of Na2FePO4F electrodes is their low intrinsic electronic conductivity. In order to study the effect of the carbon black and carbon nanotubes on the electrochemical performance of Na2FePO4F cathode material for lithium-ion batteries, Na2FePO4F, Na2FePO4F/CB and Na2FePO4F/CNT were prepared by a spray-drying method with different ratios of CB and CNT (10 and 20%). The crystal and local structure were analyzed by XRD and Mössbauer spectroscopy. The electrochemical properties were studied by galvanostatic cycling in lithium cells. The electrochemical performance is markedly better in the case of Na2FePO4F/CNT (20 wt%), with specific capacities of about 100 mAh/g (Na2FePO4F/CNT) at C/4 rate2 vs. 50 mAh/g for Na2FePO4F/CB. The characterization of Na2FePO4F/CB particles by electron microscopy revealed a carbon-poor surface and a good carbon dispersion for Na2FePO4F/CNT particles attributed to better diffusion of carbon nanotubes in the droplets during drying. References : 1-N. Eshraghi, S. Caes, A. Mahmoud, R. Cloots, B. Vertruyen, F. Boschini, Electrochim. Acta, 228 (2017) 319–324. 2-M. Brisbois, S. Caes, M-T. Sougrati, B. Vertruyen, A. Schrijnemakers, R. Cloots, N. Eshraghi, R-P. Hermann, A. Mahmoud, F. Boschini, Solar Energy Materials & Solar Cells 148 (2015) 67-72. [less ▲]

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See detailSpray-drying as a tool to disperse conductive carbon inside Na2FePO4F particles by addition of carbon black or carbon nanotubes to the precursor solution
Mahmoud, Abdelfattah ULiege; Caes, Sebastien; Brisbois, Magali et al

in Journal of Solid State Electrochemistry (2017)

In this work, Na2FePO4F-carbon composite powders were prepared by spray-drying a solution of inorganic precursors with 10 and 20 wt% added carbon black (CB) or carbon nanotubes (CNTs). In order to compare ... [more ▼]

In this work, Na2FePO4F-carbon composite powders were prepared by spray-drying a solution of inorganic precursors with 10 and 20 wt% added carbon black (CB) or carbon nanotubes (CNTs). In order to compare the effect of CB and CNTwhen added to the precursor solutions, the structural, electrochemical, and morphological properties of the synthesized Na2FePO4F-xCB and Na2FePO4F-xCNT samples were systematically investigated. In both cases, X-ray diffraction shows that calcination at 600 °C in argon leads to the formation of Na2FePO4F as the major inorganic phase. 57Fe Mössbauer spectroscopy was used as complementary technique to probe the oxidation states, local environment, and identify the composition of the iron-containing phases. The electrochemical performance is markedly better in the case of Na2FePO4F-CNT (20 wt%), with specific capacities of about 100 mAh/g (Na2FePO4F-CNT) at C/4 rate vs. 50 mAh/g for Na2FePO4F-CB (20 wt%). SEM characterization of Na2FePO4F-CB particles revealed different particle morphologies for the Na2FePO4F-CNT and Na2FePO4F-CB powders. The carbon-poor surface observed for Na2FePO4FCB could be due to a slow diffusion of carbon in the droplets during drying. On the contrary, Na2FePO4F-CNT shows a better CNT dispersion inside and at the surface of the NFPF particles that improves the electrochemical performance. [less ▲]

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See detailAnalysing operando Mössbauer spectra of battery materials: a chemometric approach to the study of NaFeO2 as positive electrode material for Na-ion batteries
Stievano, Lorenzo; Sougrati, Moulay Tahar; Darwiche, Ali et al

Conference (2017, May 19)

Among the possible positive electrode materials for Na-ion batteries, iron-based oxides have been regarded as promising solids for the reversible insertion/deinsertion of Na on the basis of their ... [more ▼]

Among the possible positive electrode materials for Na-ion batteries, iron-based oxides have been regarded as promising solids for the reversible insertion/deinsertion of Na on the basis of their abundance in the Earth’s crust. In particular, O3-type NaFeO2, easily prepared from the reaction of iron oxide and Na2CO3 at 600°C, has been identified as the most interesting one from the viewpoint of both gravimetric and volumetric energy density.[1–3] Na/NaFeO2 cells cycle through a relatively flat potential plateau between 3.3 and 3.4 V vs. Na+/Na, commonly associated with the Fe4+/Fe3+ redox couple. However, if cycling is extended above 3.5 V, other irreversible reaction plateaux appear, which completely inactivate the material. 57Fe Mössbauer spectroscopy is thus a method of choice for the study of both (1) the cycling mechanism and (2) the irreversible reactions occurring above 3.5 V. In this work, operando 57Fe Mössbauer spectra were collected during the electrochemical cycling of NaFeO2 vs. Na metal using a specifically designed in situ cell,[4] and analysed using an alternative and innovating data analysis approach based on chemometric tools such as Principal Component Analysis (PCA) and multivariate curve resolution (MCR).[5,6] This approach, which allows the unbiased extraction of all possible information from the operando data, enabled the stepwise reconstruction of the “real” spectral components occurring during the cycling of NaFeO2. In this way, a clear description of the electrochemically active iron species could be obtained, allowing a clearer comprehension of the cycling mechanisms of this material vs. sodium. Références : [1] J. Zhao, L. Zhao, N. Dimov, O. Shigeto, T. Nishida, J. Electrochem. Soc. 160 (2013) A3077. [2] H. Yoshida, N. Yabuuchi, S. Komaba, in:, ECS Meet. Abstr. MA2012-02, ECS, Honolulu, 2011, p. 1850. [3] P. Barpanda, Chem. Mater. 28 (2016) 1006. [4] J.-B. Leriche, S. Hamelet, J. Shu, M. Morcrette, C. Masquelier, G. Ouvrard, M. Zerrouki, P. Soudan, S. Belin, E. Elkaïm, F. Baudelet, J. Electrochem. Soc. 157 (2010) A606. [5] R. Tauler, Chemom. Intell. Lab. 30 (1995) 133. [6] A. Voronov, A. Urakawa, W. van Beek, N.E. Tsakoumis, H. Emerich, M. Rønning, Anal. Chim. Acta 840 (2014) 20. [less ▲]

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See detailStudy of the photocatalytic activity of Fe3+, Cr3+, La3+ and Eu3+ single-doped and co-doped TiO2 catalysts produced by aqueous sol-gel processing
Malengreaux, Charline; Pirard, Sophie ULiege; Léonard, Géraldine ULiege et al

in Journal of Alloys and Compounds (2017), 691

An aqueous sol-gel process, previously developed for producing undoped and Cu2+, Ni2+, Zn2+ or Pb2+ doped TiO2 photocatalysts with remarkably high photocatalytic activity without requiring any calcination ... [more ▼]

An aqueous sol-gel process, previously developed for producing undoped and Cu2+, Ni2+, Zn2+ or Pb2+ doped TiO2 photocatalysts with remarkably high photocatalytic activity without requiring any calcination step, has been adapted to produce Fe3+, Cr3+, La3+ or Eu3+ single-doped TiO2 photocatalysts as well as La3+-Fe3+ and Eu3+-Fe3+ co-doped TiO2 catalysts. The physicochemical properties of the obtained catalysts have been characterized using a suite of complementary techniques, including ICP-AES, XRD, UV-Vis spectroscopy, nitrogen adsorption-desorption and Fe-57 Mössbauer. The active crystalline phase is obtained without requiring any calcination step and all the different catalysts are composed of nanocrystallites of anatase with a size of 6-7 nm and a high specific surface area varying from 181 to 298 m² g-1. In this study, the effect of the NO3:Ti(IV) mole ratio used to induce the peptisation reaction during the synthesis has been studied and the results revealed that this ratio can influence significantly the textural properties of the resulting catalyst. A screening of the photocatalytic activity of the undoped and Fe3+, Cr3+, La3+ or Eu3+ single-doped and co-doped photocatalysts has been performed by evaluating the degradation of 4-nitrophenol under UV-Visible light (330 nm < λ < 800 nm). This study suggests that the photocatalytic activity is significantly influenced by the dopant nature and content with an optimal dopant content being observed in the case of Fe3+ or La3+ single-doped as well as in the case of La3+-Fe3+ and Eu3+-Fe3+ co-doped catalysts. In the case of Cr3+ single-doped catalysts, a detrimental effect of the dopant on the photocatalytic degradation of 4-nitrophenol has been observed while no significant influence of the dopant has been detected in the case of Eu3+ single-doped catalysts. The role of the different dopants in modulating the photocatalytic activity is discussed. [less ▲]

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See detailFeNCN as new molecular negative electrode materials for Li- and Na-ion
Sougrati, Moulay Tahar; Darwiche, Ali; Liu, Xiaohiu et al

Poster (2016, September 21)

We report evidence for the electrochemical activity of transition metal carbodiimides versus lithium and sodium1. In particular, the iron carbodiimide FeNCN can be efficiently used as a negative electrode ... [more ▼]

We report evidence for the electrochemical activity of transition metal carbodiimides versus lithium and sodium1. In particular, the iron carbodiimide FeNCN can be efficiently used as a negative electrode material for alkali-metal-ion batteries (Li and Na), similarly to its oxide analogue FeO. Based on 57Fe Mössbauer and infrared spectroscopy (IR) data, the electrochemical reaction mechanism can be explained by the reversible transformation of the Fe–NCN into Li/Na–NCN bonds during discharge and charge processes. These new electrode materials exhibit higher capacity compared to well-established negative electrode references such as graphite or hard carbon. Contrary to its oxide analogue, iron carbodiimide does not require heavy treatments (nanoscale tailoring, sophisticated textures, coating etc.) to obtain long cycle life with density current as high as 9 A/g for hundreds of charge/discharge cycles. Similar to the iron compound, several other transition metal carbodiimides (MxNCNy with M = Mn, Cr, Zn) can cycle successfully versus lithium and sodium. Their electrochemical activity and performances open the way to the design of a novel family of anode materials for both Li- and Na-ion batteries. [less ▲]

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See detailTRANSITION METAL CARBODIIMIDES, A NEW CLASS OF ANODE MATERIALS
Hermann, Raphaël ULiege; Sougrati, Moulay Tahar; Darwiche, Ali et al

Conference (2016, September 05)

Battery technology is central to the development of improved transportation and communication systems. The market is hungry for improved energy storage devices which motivate sustained efforts in finding ... [more ▼]

Battery technology is central to the development of improved transportation and communication systems. The market is hungry for improved energy storage devices which motivate sustained efforts in finding new anode, cathode, or electrolyte materials. In this context it is thus surprising to stumble across entirely unchartered territory as happened with our work on iron carbodiimide, FeNCN. Transition metal carbodiimides have been investigated only in the last fifteen years, although the material class is known since CaNCN was first synthesized in 1877. CaNCN is still the best known family member and has been used intensively as fertilizer. The transition metal carbodiimides can be thought of as equivalent to transition metal oxides, where the O2- is replaced by the (–N=C=N–)2- moiety. The rigid character of this carbodiimide group leads to unique structural properties, and, amazingly, for some transition metals, magnetism survives.The intriguing magnetic properties of FeNCN led us to investigate this material by iron-57 Mössbauer spectroscopy [1]. A quite complex spectrum is observed below the Néel temperature of 345 K. The spectrum consists of 5 visible lines and simplifies to an asymmetric doublet upon further cooling to 6 K, see Fig. 1, left. An in depth analysis reveals that the magnetic hyperfine field is perpendicular to the principal axis of the electric field gradient and decreases with temperature because the orbital contribution is reduced through thermal depopulation. The interesting rather open framework of the structure, of NiAs type with As replaced by NCN, with prominent diffusive channels prompted us to investigate electrochemical properties. The result of the electrochemical testing with combined in-situ XRD and Mössbauer spectroscopy reveals an outstanding reversible capacities of 600 and 400 mAh/g against Li and Na respectively and excellent resilience against high current rate cycling (9 A/g at 32 C) [2]. The scenario that emerges from combining XRD, Mössbauer and infrared spectral data is that the material undergoes a conversion mechanism that can be formulated as FeNCN(s) + 2 Li(s) ⇌ Fe(s) + Li2NCN(s). Interestingly, although the diffractograms after cycling do not exhibit any peak of the starting FeNCN material, Mössbauer spectral data confirms that a magnetic FeNCN spectrum is recovered. These observations indicate nanometric crystalline FeNCN as the endpoint Several Mx(NCN)y carbodiimides with M = Mn, Cr, Zn where investigated electrochemically and exhibit similar promising performance and cyclability. This investigation thus opens the way to the design of a whole novel family of anode materials where O is replaced by NCN and a corresponding patent[3] has been filed. References [1] M. Herlitschke, et al., New J. Chem. 2014, 38, 4670–4677. [2] M. T. Sougrati, et al., Angew. Chemie Int. Ed. 2016, 55, 5090-5095. [3] M. T. Sougrati, et al., Metal Carbodiimides and Metal Cyanamides as New Active Electrode Materials, EP15305888 (2015), European Patent pending. [less ▲]

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See detailCalcium-Iron Oxide as Energy Storage Medium in Rechargeable Oxide Batteries
Berger, Cornelius M.; Mahmoud, Abdelfattah ULiege; Hermann, Raphaël ULiege et al

in Journal of the American Ceramic Society (2016)

Rechargeable oxide batteries (ROB) comprise a regenerative solid oxide cell (rSOC) and a storage medium for oxygen ions. A sealed ROB avoids pumping loss, heat loss, and gas purity expenses in comparison ... [more ▼]

Rechargeable oxide batteries (ROB) comprise a regenerative solid oxide cell (rSOC) and a storage medium for oxygen ions. A sealed ROB avoids pumping loss, heat loss, and gas purity expenses in comparison with conventional rSOC. However, the iron oxide base storage medium degrades during charging– discharging cycles. In comparison, CaFe3O5 has improved cyclability and a high reversible oxygen storage capacity of 22.3 mol%. In this study, we analyzed the redox mechanism of this compound. After a solid-state synthesis of CaFe3O5, we verified the phase composition and studied the redox reaction by means of X-ray diffraction, Mossbauer spectrometry, and scanning electron microscopy. Results show a great potential to operate the battery with this storage material during multiple charging–discharging cycles. [less ▲]

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See detailStudy of Sn and Fe based electrode materials for Alkali-ion batteries by in situ Mössbauer spectroscopy
Mahmoud, Abdelfattah ULiege; Sougrati, Moulay Tahar; Hermann, Raphaël ULiege et al

Conference (2016, July 19)

Li-ion batteries are widely used for electrochemical energy storage, because of their high energy density and efficiency. The most significant challenges in the development of advanced Li-ion batteries ... [more ▼]

Li-ion batteries are widely used for electrochemical energy storage, because of their high energy density and efficiency. The most significant challenges in the development of advanced Li-ion batteries concern the electrode materials. Indeed, the electrodes properties critically determine the capacity, performance, and durability of alkali-ion batteries. In the past five decades, Mössbauer spectroscopy has been an important analytical technique for investigating the structural, magnetic and electronic properties of energy materials. Mössbauer spectroscopy allows simultaneous investigation of bulk and surface characteristics. It is a non-destructive technique that can follow the behavior of electrode materials during the reaction process in situ and operando [1]. Its high resolution enables the observation of all Mössbauer active phases and the measure of their relative quantities . Iron and tin containing materials are of considerable interest as electrode material for Li-ion batteries [2, 3]. In this presentation, we report in situ and operando measurements of new electrode materials based on Fe and Sn during electrochemical cycling by combining Mössbauer spectroscopy with complementary techniques (X-ray diffraction, magnetic measurements, impedance spectroscopy, etc.) to study and investigate the electrochemical behavior of the electrode materials. [less ▲]

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See detailStructure Characterization and Properties of K‑Containing Copper Hexacyanoferrate
Ojwang, Dickson O.; Grins, Jekabs; Wardecki, Dariusz et al

in Inorganic Chemistry (2016), 55

Copper hexacyanoferrate, CuII[FeIII(CN)6]2/3·nH2O, was synthesized, and varied amounts of K+ ions were inserted via reduction by K2S2O3 (aq). Ideally, the reaction can be written as CuII[FeIII(CN)6]2 ... [more ▼]

Copper hexacyanoferrate, CuII[FeIII(CN)6]2/3·nH2O, was synthesized, and varied amounts of K+ ions were inserted via reduction by K2S2O3 (aq). Ideally, the reaction can be written as CuII[FeIII(CN)6]2/3·nH2O + 2x/3K+ + 2x/3e− ↔ K2x/3CuII[FeIIxFeIII1−x(CN)6]2/3·nH2O. Infrared, Raman, and Mössbauer spectroscopy studies show that FeIII is continuously reduced to FeII with increasing x, accompanied by a decrease of the a-axis of the cubic Fm3̅m unit cell. Elemental analysis of K by inductively coupled plasma shows that the insertion only begins when a significant fraction, ∼20% of the FeIII, has already been reduced. Thermogravimetric analysis shows a fast exchange of water with ambient atmosphere and a total weight loss of ∼26wt % upon heating to 180 °C, above which the structure starts to decompose. The crystal structures of CuII[FeIII(CN)6]2/3·nH2O and K2/3Cu[Fe(CN)6]2/3·nH2O were refined using synchrotron X-ray powder diffraction data. In both, one-third of the Fe(CN)6 groups are vacant, and the octahedron around CuII is completed by water molecules. In the two structures, difference Fourier maps reveal three additional zeolitic water sites (8c, 32f, and 48g) in the center of the cavities formed by the −Cu−N−C−Fe− framework. The K-containing compound shows an increased electron density at two of these sites (32f and 48g), indicating them to be the preferred positions for the K+ ions. [less ▲]

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See detailTransition-Metal Carbodiimides as Molecular Negative Electrode Materials for Lithium- and Sodium-Ion Batteries with Excellent Cycling Properties
sougrati, Moulay Tahar; Darwiche, Ali; Liu, Xiaohiu et al

in Angewandte Chemie International Edition (2016), 55(16), 5090-5095

We report evidence for the electrochemical activity of transition-metal carbodiimides versus lithium and sodium. In particular, iron carbodiimide, FeNCN, can be efficiently used as negative electrode ... [more ▼]

We report evidence for the electrochemical activity of transition-metal carbodiimides versus lithium and sodium. In particular, iron carbodiimide, FeNCN, can be efficiently used as negative electrode material for alkali-metal-ion batteries, similar to its oxide analogue FeO. Based on 57Fe Mossbauer and infrared spectroscopy (IR) data, the electrochemical reaction mechanism can be explained by the reversiblevtransformation of the FeNCN into Li/NaNCN bonds during discharge and charge. These new electrode materials exhibit higher capacity compared to well-established negative electrode references such as graphite or hard carbon. Contrary to its oxide analogue, iron carbodiimide does not require heavy treatments (such as nanoscale tailoring, sophisticated textures, or coating) to obtain long cycle life with current density as high as 9 Ag-1 for hundreds of charge–discharge cycles. Similar to the iron compound, several other transition-metal carbodiimides Mx(NCN)y with M=Mn, Cr, Zn can cycle successfully versus lithium and sodium. Their electrochemical activity and performance open the way to the design of a novel family of anode materials. [less ▲]

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See detailÜbergangsmetallcarbodiimide als molekulare negative Elektroden- materialien für Li- und Na-Ionenbatterien mit hervorragendem Zyklisierungsverhalten
Sougrati, Moulay T.; Darwiche, Ali; Liu, Xiaohiu et al

in Angewandte Chemie (2016), 128(16), 5174--5179

Wir weisen die elektrochemische Aktivität von Übergangsmetallcarbodiimiden gegenüber Lithium und Natrium nach. Insbesondere das Eisencarbodiimid FeNCN läßt sich effektiv als negatives Elektrodenmaterial ... [more ▼]

Wir weisen die elektrochemische Aktivität von Übergangsmetallcarbodiimiden gegenüber Lithium und Natrium nach. Insbesondere das Eisencarbodiimid FeNCN läßt sich effektiv als negatives Elektrodenmaterial für Alkalimetallionenbatterien verwenden, ähnlich dem Oxidanalogon FeO. Auf der Basis von 57Fe-Mößbauer- und infrarotspektroskopischen (IR) Daten kann der elektrochemische Reaktionsmechanismus bei Entladung und Beladung durch die reversible Umwandlung von Fe-NCN- in Li/Na-NCN-Bindungen erklärt werden. Diese neuen Elektrodenmaterialien weisen höhere Kapazitäten als die etablierten negativen Referenzelektroden wie Graphit oder Hartkohlenstoff auf. Im Gegensatz zu seinem Oxidanalogon benötigt Eisencarbodiimid keine aufwendige Vorbehandlung (Nanopräparation, spezielle Texturen, Beschichtung usw.), um eine lange Lebensdauer bei Stromdichten bis zu 9 A g−1 für hunderte von Lade-/Entladezyklen zu erreichen. Ähnlich zur Eisenverbindung können einige andere Übergangsmetallcarbodiimide Mx(NCN)y mit M=Mn, Cr, Zn ebenso erfolgreich gegen Lithium und Natrium zyklisieren. Ihre elektrochemische Aktivität und Leistung öffnet den Weg zum Design einer neuartigen Klasse von Anodenmaterialien. [less ▲]

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See detailToward understanding the lithiation/delithiation process in Fe0.5TiOPO4/C electrode material for lithium-ion batteries
Lasri, K.; Mahmoud, Abdelfattah ULiege; Saadoune, I. et al

in Solar Energy Materials & Solar Cells (2016), 148

Fe0.5TiOPO4/C composite was used as anode material for LIB and exhibits excellent cycling performance when the electrode is cycled in two different voltage ranges [3.0-1.3 V] and [3.0-0.02 V] where ... [more ▼]

Fe0.5TiOPO4/C composite was used as anode material for LIB and exhibits excellent cycling performance when the electrode is cycled in two different voltage ranges [3.0-1.3 V] and [3.0-0.02 V] where different insertion mechanisms were involved. A detailed in situ XANES spectroscopy study coupled to the electrochemical analyses, clearly established that the structure of Fe0.5TiOPO4/C electrode materials is preserved when cycled between 3.0 and 1.3 V. Furthermore, a formation of new phase at the end of first discharge was evidenced, with a reversible capacity of 100 mA h g-1 after 50 cycles at C/5 rate. At highly lithiated states, [3.0-0.02 V] voltage range, a reduction-decomposition reaction highlights the Li-insertion/extraction behaviors, and low phase crystallinity is observed during cycling, in addition an excellent rate behavior and a reversible capacity of 250 mA h g-1 can still be maintained after 50 cycles at high cycling rate 5C. © 2015 Elsevier B.V. [less ▲]

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See detailMaterial properties of perovskites in the quasi-ternary system LaFeO3-LaCoO3-LaNiO3
Tietz, F.; Arul Raj, I.; Ma, Q. et al

in Journal of Solid State Chemistry (2016), 237

An overview is presented on the variation of electrical conductivity, oxygen permeation, and thermal expansion coefficient as a function of the composition of perovskites in the quasi-ternary system ... [more ▼]

An overview is presented on the variation of electrical conductivity, oxygen permeation, and thermal expansion coefficient as a function of the composition of perovskites in the quasi-ternary system LaFeO3-LaCoO3-LaNiO3. Powders of thirteen nominal perovskite compositions were synthesized under identical conditions by the Pechini method. The powder X-ray diffraction data of two series, namely La(Ni0.5Fe0.5)1-xCoxO3 and LaNi0.5-xFexCo0.5O3, are presented after the powders had been sintered at 1100 °C for 6 h in air. The measurements revealed a rhombohedral structure for all compositions except LaNi0.5Fe0.5O3 for which 60% rhombohedral and 40% orthorhombic phase was found. The maximum DC electrical conductivity value of the perovskites at 800 °C was 1229 S cm-1 for the composition LaCoO3 and the minimum was 91 S cm-1 for the composition LaCo0.5Fe0.5O3. The oxygen permeation of samples with promising conductivities at 800 °C was one order of magnitude lower than that of La0.6Sr0.4Co0.8Fe0.2O3 (LSCF). The highest value of 0.017 ml cm-2 min-1 at 950 °C was obtained with LaNi0.5Co0.5O3. The coefficients of thermal expansion varied in the range of 13.2×10-6 K-1 and 21.9×10-6 K-1 for LaNi0.5Fe0.5O3 and LaCoO3, respectively. 57Fe Mössbauer spectroscopy was used as probe for the oxidation states, local environment and magnetic properties of iron ions as a function of chemical composition. The substitution had a great influence on the chemical properties of the materials. © 2016 Elsevier Inc. All rights reserved. [less ▲]

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See detailFe3+/Iron Oxide/SiO2 Xerogel Catalysts for p-nitrophenol Degradation by Photo-Fenton Effects: Influence of Thermal Treatment on Catalysts Texture
Mahy, Julien ULiege; Tasseroul, Ludivine ULiege; Herlitscke, Marcus et al

in Materials Today: Proceedings (2016), 3(2), 464-469

Three iron xerogel catalysts were synthesized by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ... [more ▼]

Three iron xerogel catalysts were synthesized by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ions. Four thermal treatments were applied to catalysts: drying, drying-autoclaving, calcination and calcination-autoclaving. Textural characterizations show that the specific surface area is increased by calcination while materials microporosity completely collapse when using autoclaving. Based on Mössbauer spectroscopy and magnetometry measurements, only Fe3+ species were observed in xerogel catalysts. The photo-Fenton effect of these catalysts was evaluated on the degradation of p-nitrophenol in aqueous media. In the presence of H2O2, results show that this effect reachs 99% of degradation after 24 h. Mössbauer and catalytic tests are presented in another paper. [less ▲]

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See detailNa2FePO4F/multi-walled carbon nanotubes for lithium-ion batteries: Operando Mössbauer study of spray-dried composites
Brisbois, Magali; Caes, Sébastien ULiege; Sougrati, M.T. et al

in Solar Energy Materials & Solar Cells (2016), 148

In order to favor electronic conductivity in sodium iron fluorophosphate electrodes for lithium- or sodium-ion batteries, composites of Na2FePO4F with multi-walled carbon nanotubes (CNTs) were prepared by ... [more ▼]

In order to favor electronic conductivity in sodium iron fluorophosphate electrodes for lithium- or sodium-ion batteries, composites of Na2FePO4F with multi-walled carbon nanotubes (CNTs) were prepared by pilot-scale spray drying. Addition of multi-walled CNTs in the solution results in an excellent dispersion of the CNTs within the volume of Na2FePO4F and not only at the surface of the particles. Following a heat treatment at 600°C in argon in order to reach crystallization, X-ray diffraction and ex situ Mössbauer spectroscopy revealed the presence of significant amounts of Fe(III) and maghemite (γ-Fe2O3) in the powder. However, Na2FePO4F/CNTs composites exhibit good electrochemical performance when cycling against lithium, with a discharge capacity of 104mAhg-1 at C/10 rate and 90mAhg-1 at 1C rate. Therefore, operando 57Fe transmission Mössbauer spectroscopy analyses were carried out in order to investigate the evolution of the iron oxidation state during cycling. During the first discharge, all the Fe(III) is reduced to Fe(II), explaining the good electrochemical performance. [less ▲]

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See detailThermoelectric properties of the unfilled skutterudite FeSb3 from first principles and Seebeck local probes
Lemal, Sébastien ULiege; Ngoc, Nguyen; de Boor, Johannes et al

in Physical Review. B: Condensed Matter and Materials Physics (2015), 92

Using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid ... [more ▼]

Using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid functional approach for exchange-correlation. The ground state is determined to be anti-ferromagnetic with an atomic magnetic moment of 1.6 μB/Fe. The Néel temperature Tn is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33 meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6 μV/K, slightly lower than the theoretical result. The theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers. [less ▲]

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See detailCrystal structure and high-temperature properties of the Ruddlesden–Popper phases Sr3−xYx(Fe1.25Ni0.75)O7−δ (0≤x≤0.75)
Samain, Louise ULiege; Amshoff, Philipp; Biendicho, Jordi J. et al

in Journal of Solid State Chemistry (2015), 227

Abstract Ruddlesden–Popper n=2 member phases Sr3−xYxFe1.25Ni0.75O7−δ, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mössbauer spectroscopy. Both samples as ... [more ▼]

Abstract Ruddlesden–Popper n=2 member phases Sr3−xYxFe1.25Ni0.75O7−δ, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mössbauer spectroscopy. Both samples as-prepared at 1300°C under N2(g) flow and samples subsequently air-annealed at 900°C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mössbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mössbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4ppmK−1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones. [less ▲]

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