References of "Mahmoud, Abdelfattah"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailHydrothermal self-assembly of sodium manganese iron phosphate particles: Growth mechanism and electrochemical performance in lithium-ion battery
Karegeya, claude; Mahmoud, Abdelfattah ULiege; Vertruyen, Bénédicte ULiege et al

in Solid State Ionics (2017), 312

Na2Mn1.5Fe1.5(PO4)3 (NMFP) dandelion sphere-like particles were successfully synthesized via a hydrothermal route without addition of any templates or surfactants (laboratory and pilot scales). The ... [more ▼]

Na2Mn1.5Fe1.5(PO4)3 (NMFP) dandelion sphere-like particles were successfully synthesized via a hydrothermal route without addition of any templates or surfactants (laboratory and pilot scales). The hydrothermal reactor (pilot scale) is equipped with stirrer for continuous agitation of reagents during the reaction. The obtained materials were characterized by X-ray diffraction, Mössbauer spectroscopy and Scanning electron microscopy. Results show that Na2Mn1.5Fe1.5(PO4)3 samples obtained from the reaction performed at laboratory scale have hierarchical dandelion sphere-like morphology and the dandelions consist of micro-/nano-rods. On the other hand, we obtained the self-assembly nano-rods morphology for the particles prepared using hydrothermal reactor. On the basis of the experimental results, a growth mechanism of Na2Mn1.5Fe1.5(PO4)3 self-assembly and dandelion sphere-like particles was proposed. Temperature and time of hydrothermal reaction are found to be crucial parameters in controlling the growth of Na2Mn1.5Fe1.5(PO4)3 particles. In addition, investigation of the effect of continuous stirring during the hydrothermal reaction shows that the reaction time can be optimized to obtain Na2Mn1.5Fe1.5(PO4)3 with small particles size. The influence of stirring on the NMFP morphology has been clearly evidenced. Indeed, the stirring leads to homogeneous particles. Cycling studies have shown that the synthesized Na2Mn1.5Fe1.5(PO4)3 dandelions materials exhibit specific discharge capacities of about 62 and 57 mAh g−1 equivalent to about 1.2 and 1.05 lithium ions de-intercalated at C/15 and C/10 current density respectively. [less ▲]

Detailed reference viewed: 7 (1 ULiège)
Full Text
See detailElectrode materials for Li/Na-ion batteries: Improving electrochemical performance through carbon addition during synthesis
Mahmoud, Abdelfattah ULiege; Karegeya, Claude; Eshraghi, Nicolas ULiege et al

Poster (2017, October 12)

Lithium-ion batteries have been widely applied as a power source for portable and stationary energy storage systems. Na-ion batteries are considered to be an alternative to Li-ion batteries owing to the ... [more ▼]

Lithium-ion batteries have been widely applied as a power source for portable and stationary energy storage systems. Na-ion batteries are considered to be an alternative to Li-ion batteries owing to the natural abundance of sodium. New electrode materials are required to increase the energy density of Li/Na-ion batteries. In this study, we show that the addition of the carbon sources during the synthesis leads to control the particles size and morphology and improve their conductivity properties that enhance the electrochemical performance [1-5]. In order to study the effect of the carbon on the structural, morphological and electrochemical properties of the prepared materials by a spray-drying [1-3] or hydrothermal methods [4, 5]. The crystal and local structure were analyzed by XRD and Mössbauer spectroscopy. The morphological properties were characterized by SEM and TEM. The carbon content was determined by TG/TDA and carbon analyzer. The electrochemical properties were studied by impedance spectroscopy and galvanostatic cycling in lithium cells. Finally, the reaction mechanism during cycling was investigated using operando XRD technique. 1- A. Mahmoud, S. Caes, M. Brisbois, R.P. Hermann, L. Berardo, A. Schrijnemakers, C. Malherbe, G. Eppe, R. Cloots, B. Vertruyen, F. Boschini, Spray-drying as a tool to disperse conductive carbon inside Na2FePO4F particles by addition of carbon black or carbon nanotubes to the precursor solution, J. Solid State Electrochem. (2017) 1–10. 2- N. Eshraghi, S. Caes, A. Mahmoud, R. Cloots, B. Vertruyen, F. Boschini, Sodium vanadium (III) fluorophosphate/carbon nanotubes composite (NVPF/CNT) prepared by spray-drying: good electrochemical performance thanks to well-dispersed CNT network within NVPF particles, Electrochim. Acta, 228 (2017) 319–324. 3- M. Brisbois, S. Caes, M-T. Sougrati, B. Vertruyen, A. Schrijnemakers, R. Cloots, N. Eshraghi, R-P. Hermann, A. Mahmoud, F. Boschini, Na2FePO4 F/multi-walled carbon nanotubes for lithium-ion batteries: Operando Mössbauer study of spray-dried composites, Solar Energy Materials & Solar Cells 148 (2016) 67-72. 4- C. Karegeya, A. Mahmoud, B. Vertruyen, F. Hatert, R.P. Hermann, R. Cloots, F. Boschini, One-step hydrothermal synthesis and electrochemical performance of sodium-manganese-iron phosphate as cathode material for Li-ion batteries, J. Solid State Chem.253 (2017) 389–397. 5- C. Karegeya, A. Mahmoud, R. Cloots, B. Vertruyen, F. Boschini, Hydrothermal synthesis in presence of carbon black: Particle-size reduction of iron hydroxyl phosphate hydrate for Li-ion battery, Electrochimica Acta. Electrochim. Acta 250 (2017) 49–58. [less ▲]

Detailed reference viewed: 87 (12 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 12 (3 ULiège)
Full Text
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 ▲]

Detailed reference viewed: 22 (4 ULiège)
Full Text
Peer Reviewed
See detailComparison of the electrochemical performance of Li4Ti5O12 spinel as negative electrodes for lithium-ion batteries prepared by sol gel and spray drying methods
Mahmoud, Abdelfattah ULiege; Piffet, Caroline ULiege; Berardo, Loris ULiege et al

Poster (2017, September 05)

Energy is considered as the lifeblood of modern society. Rechargeable batteries are the most promising to meet the human needs concerning the energy storage thanks their high energy density and high ... [more ▼]

Energy is considered as the lifeblood of modern society. Rechargeable batteries are the most promising to meet the human needs concerning the energy storage thanks their high energy density and high energy efficiency. Most difficult challenges of the development of promising rechargeable batteries concern the electrode materials. Li4Ti5O12 (LTO) is one the most promising anode materials for Li-ion batteries, as it demonstrates very stable cycling stability and excellent safety. Its high operating potential (~1.5 V) allows to avoid the formation of SEI during the first cycle. The three-dimensional structure offers LTO excellent reversibility due to the near zero volume strain during the Li+ ion intercalation and deintercalation cycling. The main objective of this study on LTO samples was to evidence the effect of synthesis method and thermal conditions on their structural, morphological and electrochemical properties [1, 2]. The results demonstrate the strong influence of the synthesis route (Sol-Gel and spray-drying methods) and the thermal treatment on the capacity, cyclability and rate capability of the LTO spinel in Li-half-cell and Li-ion full-cell (see Figure 1). References [1] A. Mahmoud, J. M. Amarilla, K. Lasri, I. Saadoune, Electrochim. Acta 93 (2013) 163-172. [2] A. Mahmoud, J. M. Amarilla, I. Saadoune, Electrochim. Acta 163 (2015) 213-222. [less ▲]

Detailed reference viewed: 50 (11 ULiège)
Full Text
See detailElectrochemical Mechanism of TiMnSn4 as Anode Material for Li-ion Batteries
Lippens, Pierre-Emmanuel; Jumas, Jean-claude; Olivier-Fourcade, Josette et al

Conference (2017, September 04)

Li-ion batteries are widely used in portable electronic devices, electric vehicles or energy storage systems for intermittent energy sources, due to their high energy density, light weight and long cycle ... [more ▼]

Li-ion batteries are widely used in portable electronic devices, electric vehicles or energy storage systems for intermittent energy sources, due to their high energy density, light weight and long cycle life. However, the performances must be continuously improved, which requires the development of new electrode materials. Carbon is commercially used for the anode but its specific capacity is limited to 372 mAh g-1 due to the electrochemical insertion mechanism involving only 1 Li per 6 C. In order to increase the specific capacity, Sn was considered as electrochemically active element although it is about ten times heavier than C. This is due to the alloying/dealloying mechanism with up to 4.4 Li per Sn, providing a theoretical capacity of 992 mAh g-1. However, the Sn ↔ Li4.4Sn reversible transformations are associated with large volume variations responsible for capacity fading.Tin intermetallic compounds of the form MSnx, where M is a transition metal, were proposed to overcome this problem. The first lithiation transforms the pristine material into Li7Sn2/M nanocomposites where the M nanoparticles are expected to buffer the volume variations [1]. However, the delithiation process is more complex involving a possible back reaction of M with Sn, which could play a crucial role in the cycling stability. Such reaction was observed for Ni3Sn4 [2] and MnSn2 [3] but not for FeSn2 [4]. In addition, TiSnx intermetallics show very poor electrochemical activity [5]. The present work concerns the tin based ternary phase TiMnSn4 as new anode material for Li-ion batteries. This compound is of particular interest because it contains two different transition metals that are expected to react differently with Sn during delithiation, if we consider the previous results obtained for MnSnx and TiSnx. TiMnSn4 was obtained by mechanosynthesis to optimize the microstructure and characterized by different experimental tools and DFT (density functional theory) calculations. We propose an analysis of the reaction mechanism based on operando X-ray diffraction and 119Sn Mössbauer spectroscopy combined with a DFT interpretation of the electrochemical potential curve. References 1) M. Chamas, M.T. Sougrati, C. Reibel, P.E. Lippens, Chem. Mater. 25, 2410 (2013). 2) K.K.D. Ehinon, S. Naille, R. Dedryvère, P.E. Lippens, J.C. Jumas, D. Gonbeau, Chem. Mater. 20, 5388 (2008). 3) A. Mahmoud, M. Chamas, J.C. Jumas, B. Philippe, R. Dedryvère, D. Gonbeau, I. Saadoune, P.E. Lippens, J. Power Sources 244, 246 (2013). 4) M. Chamas, P.E. Lippens, J.C. Jumas, K. Boukerma, R. Dedryvère, D. Gonbeau, J. Hassoun, S. Panero, B. Scrosati, J. Power Sources 196, 7011 (2011). 5) A. Ladam, L. Aldon, P.E. Lippens, J. Olivier-Fourcade, J.C. Jumas, C. Cenac-Morthe, Hyperfine Interact. 237, 51 (2016). [less ▲]

Detailed reference viewed: 26 (6 ULiège)
See detailUp-scalable spray-drying synthesis of Na2Ti3O7
Piffet, Caroline ULiege; Vertruyen, Bénédicte ULiege; Mahmoud, Abdelfattah ULiege et al

Poster (2017, September)

Detailed reference viewed: 26 (5 ULiège)
Full Text
See detailPreparation and characterization of Silicon-carbon composite powders using recycled Silicon from solar cells as anode material in Li-ion batteries
Eshraghi, Nicolas ULiege; Mahmoud, Abdelfattah ULiege; Berardo, Loris ULiege et al

Poster (2017, September)

Currently, silicon (Si) coming from the recycling of solar cells is a non-valued fraction. The principal aim of this work is the development of silicon recovered during the dismantling of solar panels as ... [more ▼]

Currently, silicon (Si) coming from the recycling of solar cells is a non-valued fraction. The principal aim of this work is the development of silicon recovered during the dismantling of solar panels as electrode material for Li-ion batteries. The main technological challenge associated with the use of silicon in this type of application is to control the volume expansion during charge/discharge cycles. This drawback could be avoided through the formation of Silicon/carbon composites in which the size of the silicon particles and their dispersion must be controlled. In this research, we develop a carbon matrix consisting of graphene or carbon nanotubes (CNT) that allow the incorporation of silicon particles coated with a carbon layer (Si@C/C). The process is divided in two main steps : I) the grinding of leached Si wafer pieces in order to extract pure Si powder and then a mixed aqueous suspension of this recycled Si and an organic carbon source (Acetic acid, Ascorbic acid or Lactose) is spray-dried followed by heat treatment to generate the coating of silicon particles with carbon (Si@C). Then, II) aqueous suspension of Si@C and graphene/CNT is spray dried and calcined to obtain the final composite structure (Si@C/C). The morphology of composite materials is analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical performance of Si@C/C composites are characterized by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy (EIS). [less ▲]

Detailed reference viewed: 23 (4 ULiège)
Full Text
See detailRecycling of silicon used in solar cells to prepare silicon-carbon composite powders as anode material in li-ion batteries
Eshraghi, Nicolas ULiege; Mahmoud, Abdelfattah ULiege; Berardo, Loris ULiege et al

Poster (2017, September)

Currently, silicon (Si) coming from the recycling of solar cells is a non-valued fraction. The principal aim of this work is the development of silicon recovered during the dismantling of solar panels as ... [more ▼]

Currently, silicon (Si) coming from the recycling of solar cells is a non-valued fraction. The principal aim of this work is the development of silicon recovered during the dismantling of solar panels as an electrode material for lithium or sodium batteries. The main technological challenge associated with the use of silicon in this type of application is to control the volume expansion during charge/discharge cycles. This problem could be solved through the synthesis of Silicon/carbon composites in which the size of the silicon particles and their dispersion must be controlled [1–4]. We develop a carbon matrix consisting of graphene or carbon nanotubes (CNT) that allow the incorporation of silicon particles coated with a carbon layer (Si@C/C). The process is divided in two main steps. In the first step, Si wafer pieces are ground to prepare Si powder and then a mixed suspension of Si and an organic carbon source (Acetic acid, Ascorbic acid or Lactose) is spray-dried followed by heat treatment to generate the coverage of silicon particles with carbon (Si@C). In the second step, aqueous suspension of Si@C and graphene/CNT is spray dried and heat treated to obtain the final composite structure. The morphology of composite materials is analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical performance of Si@C/C composites are characterized by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy (EIS). [less ▲]

Detailed reference viewed: 42 (8 ULiège)
Full Text
Peer Reviewed
See detailExperimental and theoretical investigation of SrFe12O19 nanopowder for permanent magnet application
Abraime, Brahim; Ait tamerd, Mohamed; Mahmoud, Abdelfattah ULiege et al

in Ceramics International (2017)

Strontium M-type hexagonal ferrites were synthesized at different calcination temperatures (800 °C, 1000 °C and 1100 °C) using sol-gel autocombustion method. Thermogravimetric analysis (TGA), X-ray ... [more ▼]

Strontium M-type hexagonal ferrites were synthesized at different calcination temperatures (800 °C, 1000 °C and 1100 °C) using sol-gel autocombustion method. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy (MS) and superconducting quantum interference device magnetometer (SQUID) techniques were used to characterize crystal structure, phase composition, morphology and magnetic properties. TGA gives T = 800 °C as beginning of suitable calcination. Hexaferrite structure of single phase is obtained according to XRD results for all samples with crystallite size between 28 nm and 35 nm. SEM images show the growth of grain size with increasing of annealing temperature. (BH)max is calculated based on SQUID results and shows an enhancement between T = 800 °C and T = 1000 °C of 25%. The magnetic properties observed at low temperature are explained and confirmed by ab-initio calculations [less ▲]

Detailed reference viewed: 25 (3 ULiège)
Full Text
Peer Reviewed
See detailHydrothermal synthesis in presence of carbon black: Particle-size reduction of iron hydroxyl phosphate hydrate for Li-ion battery
Karegeya, Claude ULiege; Mahmoud, Abdelfattah ULiege; Cloots, Rudi ULiege et al

in Electrochimica Acta (2017), 250

Iron hydroxyl phosphate hydrate Fe1.19(PO4)(OH)0.57(H2O)0.43 (FPHH) was obtained by hydrothermal synthesis at 220 °C for 6 hours. Addition of carbon black to the solution before hydrothermal treatment led ... [more ▼]

Iron hydroxyl phosphate hydrate Fe1.19(PO4)(OH)0.57(H2O)0.43 (FPHH) was obtained by hydrothermal synthesis at 220 °C for 6 hours. Addition of carbon black to the solution before hydrothermal treatment led to a reduction of the FPHH particle size from ∼10 μm in the carbon-free compound to ∼300–500 nm in the FPHH-10%C and FPHH-20%C composite with a good dispersion of conducting carbon black. X-ray diffraction, 57Fe Mossbauer spectroscopy and a thermal decomposition study showed that the addition of carbon black did not interfere with the formation of the FPHH phase. Thanks to its favorable microstructural characteristics, the FPHH-10%C and FPHH-20%C material exhibited good performance as positive electrode for Li-ion battery, with high initial discharge capacities of 150, 128 and 112 mAh g−1 at 0.25C, 0.5C and 1C rates respectively and 99% capacity retention after 150 cycles at 2C. These results show that addition of solid carbon directly into the solution prior to hydrothermal treatment is a simple and effective way to reduce particle size and also to improve electronic conductivity by dispersing conductive carbon around the active material. This approach is easily transferable to other compounds prepared by hydrothermal synthesis, in order to control particle size while retaining the advantage of crystallization at low temperature. [less ▲]

Detailed reference viewed: 28 (5 ULiège)
Full Text
Peer Reviewed
See detailCation Distribution Dependent Magnetic Properties in CoCr 2-x Fe x O 4 (x= 0.1 to 0.5): EXAFS, Mӧssbauer and Magnetic Measurements
Kumar, Durgesh; Banerjee, Alok; Mahmoud, Abdelfattah ULiege et al

in Dalton Transactions (2017), 46

In this report, we have examined the evolution of the structure and rich magnetic transitions such as a paramagnetic to ferrimagnetic phase transition at the Curie temperature (TC), spiral ordering ... [more ▼]

In this report, we have examined the evolution of the structure and rich magnetic transitions such as a paramagnetic to ferrimagnetic phase transition at the Curie temperature (TC), spiral ordering temperature (TS) and lock-in temperature (TL) observed in the CoCr2O4 spinel multiferroic after substituting Fe. The crystal structure, microstructure and cation distribution among the tetrahedral (A) and octahedral (B) sites in the spinel lattice are characterised by X-ray diffraction, transmission electron microscopy, Extended X-ray Absorption Fine Structure (EXAFS) and Mössbauer spectroscopy. Due to the same radial distances of the first coordination shell in both tetrahedral and octahedral environments observed in EXAFS spectra, the position of the second coordination shell specifies the preference of more Fe ions towards the A site at x = 0.1. At x = 0.5, more Fe ions favour the B site. The cation distribution quantitatively obtained from the Mössbauer spectral analysis shows that while 60% of Fe ions occupy the A site in x = 0.1, 40% occupy it in x = 0.5. Surprisingly at x = 0.3, Fe ions are distributed equally among the A and B sites. dc magnetization reveals an increase in TC from 102 K to 200 K and in TS from 26 to 40 K with an increase in Fe concentration, indicating an enhancement in A–B exchange interaction at the expense of B–B. No report has until now demonstrated such an enhancement in TS either in pure or in doped CoCr2O4. Furthermore, frequency-dependent ac susceptibility (χ) data fitted with different phenomenological models such as the Néel–Arrhenius, Vogel–Fulcher and power law confirm a spin-glass and/or cluster-glass behaviour in nanoparticles of CoCr2−xFexO4. [less ▲]

Detailed reference viewed: 15 (3 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 33 (12 ULiège)
Full Text
Peer Reviewed
See detailHighly efficient doped nanocristalline TiO2 for water Treatment
Mahy, Julien ULiege; Léonard, Géraldine ULiege; Zubiaur, Anthony ULiege et al

Conference (2017, July 13)

Detailed reference viewed: 37 (9 ULiège)
Full Text
Peer Reviewed
See detailOne-step hydrothermal synthesis and electrochemical performance of sodium-manganese-iron phosphate as cathode material for Li-ion batteries
Karegeya, Claude ULiege; Mahmoud, Abdelfattah ULiege; Vertruyen, Bénédicte ULiege et al

in Journal of Solid State Chemistry (2017), 253

The sodium-manganese-iron phosphate Na2Mn1.5Fe1.5(PO4)3 (NMFP) with alluaudite structure was obtained by a one-step hydrothermal synthesis route. The physical properties and structure of this material ... [more ▼]

The sodium-manganese-iron phosphate Na2Mn1.5Fe1.5(PO4)3 (NMFP) with alluaudite structure was obtained by a one-step hydrothermal synthesis route. The physical properties and structure of this material were obtained through XRD and Mössbauer analyses. X-ray diffraction Rietveld refinements confirm a cationic distribution of Na+ and presence of vacancies in A(2)’, Na+ and small amounts of Mn2+ in A(1), Mn2+ in M(1) , 0.5 Mn2+ and Fe cations (Mn2+,Fe2+ and Fe3+) in M(2), leading to the structural formula Na2Mn(Mn0.5Fe1.5)(PO4)3. The particles morphology was investigated by SEM. Several reactions with different hydrothermal reaction times were attempted to design a suitable synthesis protocol of NMFP compound. The time of reaction was varied from 6 to 48 hours at 220°C. The pure phase of NMFP particles was firstly obtained when the hydrothermal reaction of NMFP precursors mixture was maintained at 220°C for 6 hours. When the reaction time was increased from 6 to 12, 24 and 48 hours, the dandelion structure was destroyed in favor of NMFP micro-rods. The combination of NMFP (NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H) structure refinement and Mössbauer characterizations shows that the increase of the reaction time leads to the progressive increment of Fe(III) and the decrease of the crystal size. The electrochemical tests indicated that NMFP is a 3 V sodium intercalating cathode. The comparison of the discharge capacity evolution of studied NMFP electrode materials at C/5 current density shows different capacities of 48, 40, 34 and 34 mAhg-1 for NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H respectively. Interestingly, all samples show excellent capacity retention of about 99 % during 50 cycles. [less ▲]

Detailed reference viewed: 35 (5 ULiège)
Full Text
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 ▲]

Detailed reference viewed: 103 (3 ULiège)
Full Text
See detailStructural and Magnetic Properties of Nanosized strontium Hexaferrite Powders: Experimental and theoretical investigation
Abraime, Brahim; Ait Tamerd, Mohamed; Mahmoud, Abdelfattah ULiege et al

Poster (2017, May 18)

Strontium M-type hexagonal ferrites were synthesized at different calcination temperatures (800 °C, 1000°C and 1100 °C) using sol-gel autocombustion method. Thermogravimetric analysis (TGA), X-ray ... [more ▼]

Strontium M-type hexagonal ferrites were synthesized at different calcination temperatures (800 °C, 1000°C and 1100 °C) using sol-gel autocombustion method. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy (MS) and superconducting quantum interference device magnetometer (SQUID) techniques were used to characterize crystal structure, phase composition, morphology and magnetic properties. TGA gives T=800 °C as beginning of suitable calcination. Hexaferrite structure of single phase is obtained according to XRD results for all samples with crystallite size between 28 nm and 35 nm. SEM images show the growth of grain size with increasing of annealing temperature. (BH)max is calculated based on SQUID results and shows an enhancement between T=800°C and T= 1000°C of 25%. The magnetic properties observed at low temperature are explained and confirmed by ab-initio calculations. [less ▲]

Detailed reference viewed: 58 (2 ULiège)
Full Text
See detailMécanismes de vieillissement des anodes à base de FeSn2 pour batteries Li-ion
Chamas, Mohamad; Mahmoud, Abdelfattah ULiege; Tang, junlei et al

Poster (2017, May 18)

Les intermétalliques d’étain ont été proposés comme matériaux d’anode pour batteries Li-ion à forte densité d’énergie car leur capacité spécifique est bien supérieure à celle des anodes commerciales à ... [more ▼]

Les intermétalliques d’étain ont été proposés comme matériaux d’anode pour batteries Li-ion à forte densité d’énergie car leur capacité spécifique est bien supérieure à celle des anodes commerciales à base de carbone. Le mécanisme électrochimique est basé sur la transformation irréversible de FeSn2 en un composite formé de nanoparticules de fer et de Li3.5Sn lors de la première lithiation, puis de réactions réversibles modifiant la composition de Li3.5Sn, les particules de fer assurant la dispersion de ces particules à base d’étain [1]. Cependant, nous avons observé que l’électrode lithiée était instable dans le temps conduisant à l’autodécharge progressive de la batterie [2]. Ce phénomène de vieillissement a été caractérisé par spectrométrie Mössbauer du 57Fe et de 119Sn, par spectroscopie d’impédance et par mesures magnétiques (Figure 1). On montre que le composite Fe/Li3.5Sn se délithie progressivement au cours du temps conduisant à un composite faiblement lithié Fe/LixSn avec x<1. Les nanoparticules de fer sont stables et ne réagissent pas avec LixSn. Les atomes de lithium libérés réagissent avec l’électrolyte et modifient la morphologie de la couche SEI (Surface Electrolyte Interphase) située à la surface des particules LixSn du composite.[1] M. Chamas, M. T. Sougrati, C. Reibel, P.E. Lippens, Chem. Mater. 25, 2410 (2015). [2] M. Chamas, A. Mahmoud, J. Tang, S. Panero, M. T. Sougrati, P. E. Lippens, J. Phys Chem. C 121, 217 (2017). [less ▲]

Detailed reference viewed: 29 (3 ULiège)
Full Text
See detailAn easy route to synthesis black phosphorus at low pressure and soft conditions
Tiouitchi, Ghassane; Hamedoun, Mohammed; El Kenz, Abdallah et al

Conference (2017, May 11)

Black phosphorus a promising candidate for large application, due to his variety of structural and physical properties, can be prepared by a very low-coast reaction route with high purity and ... [more ▼]

Black phosphorus a promising candidate for large application, due to his variety of structural and physical properties, can be prepared by a very low-coast reaction route with high purity and crystallinity. Black phosphorus is prepared from red phosphorus at 873K under reduced pressure using a simple and low cost catalytic system. The quality of crystal with lattice parameters a=3.31Å, b=10.48Å, c=4.37Å can be approved by a series of characterizations like scanning microscopy electron (SEM), energy dispersive spectrometry (EDX), Raman spectroscopy and powder X-rays. The new preparation method of black phosphorus represents an easy, effective and low cost approach to avoid complicated preparative setups, toxic catalysts, or “dirty” flux methods and is of general interest in elemental chemistry. [less ▲]

Detailed reference viewed: 118 (4 ULiège)