With the growing demand for air travel and the urgent need for a sustainable future, adopting technologies enabling carbon-neutral flying is essential. In this context, the EU-funded HYdrogen eLectrical Engine Novel Architecture (HYLENA) project aims to reshape aviation by advancing energy systems, materials science, and transportation technologies. HYLENA addresses this challenge by developing a novel engine concept that integrates Solid Oxide Fuel Cells (SOFCs) into an aircraft engine (Figure 1), utilizing the high exergetic waste heat of the SOFC in a downstream turbine in addition to the electrical energy. The design combines an electric motor, a turbomachinery and H 2 -fueled SOFCs to achieve unparalleled performance with no CO 2 emissions and low NO x levels, while increasing efficiency by up to 65 % related to the shaft power. The HYLENA consortium includes AIRBUS, three leading European universities (LEPMI/GRENOBLE-INP, Leibniz University Hannover, and Technische Universiteit Delft), and two renowned research institutes (Bauhaus Luftfahrt and German Aerospace Center), supported by an advisory board to ensure market and societal impact. Key objectives include identifying optimal SOFC technologies throughout experimental, simulation and scouting activities for sustainable aviation, determining compact and lightweight stack designs, performing thermodynamic cycle simulations to evaluate the efficiency and low hydrogen requirements of the concept while minimizing weight and complexity. To ensure optimal performance, durability, and integration, it is essential to investigate the SOFC’s performance under various conditions and explore new architectures. A critical challenge is component degradation, which is driven by complex mechanisms influenced by operating parameters. This work investigates the performance of state-of-the-art anode-supported single SOFCs (Ni-YSZ/YSZ/GDC/LSCF) as a function of H 2 /air gas inlet rates, temperature (700 – 850 o C), and cathode inlet gas composition (O 2 , H 2 O, CO 2 , and SO 2 ). Experiments were performed to investigate the short-term influence of these parameters on SOFC performance using electrochemical impedance spectroscopy (EIS), and steady-state i-V-P curves. Insufficient hydrogen or air supply can limit cell performance and therefore tests were performed in a 3:1 O 2 :H 2 ratio to ensure excess oxygen. The power density increased with gas flow rates up to 20/60 mL·min -1 ·cm -2 , reaching 1.1 W·cm -2 with a 65 % of H 2 utilization at 0.75 V. No further significant improvements were observed at higher rates. Indeed, higher H 2 flow reduced the fuel utilization factor and negatively affected system economics without enhancing performance. At lower temperatures, the lower YSZ electrolyte conductivity yielded an increased cell ohmic resistance and reduced its power output. Additionally, the activation overpotential, reflecting irreversible phenomena related to electrochemical reactions, was more significant. Figure 2 shows i-V-P curves and impedance spectra under polarization (cell voltage = 0.75 V) recorded at 800 °C for pO 2 varying between 0.05 atm and 0.21 atm. At 800 o C and pO 2 = 0.21 atm, a power density of 1 W·cm -2 was achieved with a 45 % O 2 utilization. Reducing pO 2 to 0.05 atm lowered the power density to 0.5 W·cm -2 with an 85 % O 2 utilization. This highlights the effect of concentration overpotential (due to gas conversion losses and diffusion overpotentials) on SOFC performance as shown by the limiting current density in Figure 2a. This effect is also evident in the impedance spectra (Fig. 2b), as polarization resistances increase with decreasing pO 2 . At 0.21 atm, the total resistance increased from ~ 0.2 Ω·cm 2 to 3 Ω·cm 2 at 0.05 atm. Post-mortem X-ray diffraction and electron microscopy were used to investigate structure and microstructure changes in the SOFC. Overall, the results indicate that surface reaction kinetics on the electrodes vary with different operating parameters and gas composition. The collected experimental performance data will be used to validate SOFC (single cell and stack) modeling, including multi-physics analysis, performance evaluation, and future projections. Figure 1

CO 2 levels in the atmosphere are rising at an ever-increasing rate, from 0.5 to 2 ppm/year [1] in the last fifty years. It is therefore urgent to reduce the concentration of CO 2 in the atmosphere. Currently, several methods have been developed to address this issue, one of which is the capture and conversion of CO 2 into low-carbon chemicals. Among these different CO 2 conversion technologies, Solid Oxide Electrolysis Cells (SOECs) have been identified as one of the most promising devices for the direct electrolysis of CO 2 into CO [2-3] with high efficiency [4 -5]. The most critical component in these cells is the cathode material. Indeed, carbon deposition is observed on Ni-YSZ electrodes during high temperature electrolysis. Our aim is to improve the cathodic performance of SOECs by using strontium-doped lanthanum ferrite (La 0.8 Sr 0.2 ) 0.95 FeO 3- δ (LSF) as the cathode material. The electrochemical activity and stability of screen-printed LSF on a 1 mm thick dense electrolyte membrane (ZrO 2 ) 0.95 (Y 2 O 3 ) 0.08 (YSZ, Yttria Stabilized Zirconia) were characterized in a three-electrodes configuration symmetrical cell. Electrochemical impedance spectroscopy diagrams at Open Circuit Potential (OCP) and under cathodic polarization as well as steady-state i-V curves were recorded in three atmospheres (Air, Argon and CO 2 ) between 600 and 800°C. At low P(O 2 ) (Argon et CO 2 ), the polarization resistance cannot be accurately determined for the chosen measuring frequency range. For such a determination, a cathodic polarization higher than 0.6 V must be applied (Fig. 1). Similar characterizations were performed on a single electrolysis cell based on YSZ electrolyte by using a screen-printed LSM (La 0.7 Sr 0.3 MnO 3 ) as the anode material. The anode chamber contains synthetic air and CO 2 was fed into the cathode chamber at a gas flow rate of 40 and 20 mL.min -1 .cm -2 (synthetic air, CO 2 ). The cell polarization resistance was of 4.88 W.cm 2 at a voltage of 1.8 V and a current density of 65 mA.cm -2 was measured at 800°C for a cell voltage of 1.8 V (Fig 2), corresponding to a CO 2 conversion of 9%. It is worth noting that the reduction of CO 2 was likely to begin for a cell voltage higher than 0.8 V (Fig. 2), in agreement with results from three-electrode measurements. Finally, the exsolution of iron from the B site of LSF perovskite has been investigated. This involves reducing LSF in hydrogen to trigger the displacement of iron from the bulk to the surface of LSF as metallic particles in order to activate and enhance the electrochemical properties of ceramic oxides [6]. The properties of reduced and unreduced LSF electrodes will be compared and the effect of Fe for CO 2 electrolysis will be discussed. [1] J. G. Canadell, et al ., Proc Natl Acad Sci U S A . 2007 , 104(47), 18866. [2] S.B. Liu, et al. , J. Mater. Chem. A 2016 , 4, 17521. [3] S. Liu, et al. , J. Mater. Chem. A 2017 , 5, 2673. [4] J.T.S. Irvine et al ., Nat.Energy 2016 , 1, 15014. [5] A. Butler and H. Spliethoff, Renewable and Sustainable Energy Reviews 2018 , 82, 2440. [6] Shiqing Hu Journal of Power Sources 485 2021 229343 This work has benefited from government funding managed by the Agence Nationale de la Recherche under the IDEX Grenoble Alpes University Agreement (reference ANR-15-IDEX-02) and the Centre of Excellence for Multifunctional Architectural Materials (reference ANR-10-LABX-44-01) of the « Investments for the Future » program. Figure 1

The limited resources of lithium stimulated the research work to develop new polyanionic cathode materials for sodium-ion batteries. The Na2M22+Fe3+(PO4)(3) (M = Mn, Ni and Co) phases were prepared by autocombustion method assisted by glycine. Structural, morphology, thermal, electrical and electrochemical properties have been investigated. Its structures were determined using Xray powder diffraction and Rietveld method refinements. The two compounds Na2M22+Fe3+(PO4)(3) (M = Mn and Co) are alluaudite-type. Both compounds crystallize in monoclinic system with the space group C2/c and similar parameters: a = 12.0337(3) angstrom, b = 12.6268(3) angstrom, c = 6.5070(1) angstrom, beta = 114.563(2)degrees for Na2M22+Fe3+(PO4)(3) (NMFP) and a = 11.7597(3) angstrom, b = 12.4579(3) angstrom, c = 6.4607(1) angstrom, beta = 113.968(1)degrees for Na2Co2Fe(PO4)(3) (NCFP). The NaNiFe2(PO4)(3) (NNFP) compounds crystallize in orthorhombic system with the space group Imma and unit cell parameters: a = 10.3993(1) angstrom, b= 13.1966(1) angstrom, c = 6.4955(1) angstrom. The composition and morphology of the compounds were checked by energy dispersive spectroscopy coupled with scanning electron microscope. The thermal analysis confirmed the allotropic transition of the three materials from monoclinic to orthorhombic symmetry with the changing of divalent transitions metal ion. The electrical conductivity results of indicated that NNFP has the lowest value of activation energy of value= 0.63 eV owing to the large size of open channels existed in the orthorhombic symmetry. The electrochemical cycling results showed that NMFP cathode delivered the maximum storage capacity of about 94.2 mAh/g which correspond to coloumbic efficiency of about 75.5% after the initial cycling. (C) 2022 Elsevier B.V. All rights reserved.

Cu and Ni substitutions are investigated at spinel MFCO (Manganese Iron Cobalt Oxide) components using a variety of characterization techniques, including XRD, XPS, RAMAN spectroscopy, SEM, TGA, dilatometer measurements, and electrochemical investigations. MnCu0.25Fe0.25Ni0.5CoO4 and MnCu0.5Fe0.25Ni0.25CoO4 spinel oxides were prepared and evaluated as a copper-nickel MFCO protective coating layer on the com-mercially available 316 L stainless steel interconnect for intermediate temperature solid oxide fuel cells (IT-SOFCs). XRD analysis indicates that both powder samples contain a single phase with a cubic structure. In both compounds, mixed Mn3+/Mn4+, Co2+/Co3+, and Cu+/Cu2+ couples are found, showing that co-doping of Ni and Cu into the MFCO spinel resulted in the redistribution of Mn and Co ions (Mn3+, Mn4+, Co2+, and Co3+) into the octahedral sites, which contributed to the increase in electrical conductivity. MnCu0.5Fe0.25Ni0.25CoO4 exhibited a maximum conductivity of 54 S cm-1 at 750 degrees C. Following the area -specific resistance (ASR) of the scale/coating during heating and cooling cycles was used to evaluate the protective action of the coating applied to 316 L stainless steel. Postmortem microstructural analysis of the screen-printed coatings showed good protection against chromium diffusion.

Substitution of Cu and Ni at spinel MFCO materials is investigated by various characterization techniques such as XRD, XPS, RAMAN spectroscopy, SEM, TGA, dilatometer measurements and electrochemical measurements. MnCu0.25Fe0.25Ni0.5CoO4 and MnCu0.5Fe0.25Ni0.25CoO4 spinel oxides were prepared and evaluated as a copper-nickel MFCO protective coating layer on the commercially available 316L stainless steel interconnect for intermediate temperature solid oxide fuel cells (IT-SOFCs). Single phase of both powder samples with cubic structure are identified using XRD. XPS results confirm that mixed Mn3+/Mn4+, Co2+/Co3+ and Cu+/Cu2+ in couples exist in both compounds, and revealed that co-doping of Ni and Cu into the MFCO spinel resulted in redistribution of Mn and Co ions (Mn3+, Mn4+, Co2+ and Co3+) into the octahedral sites, which increased the electrical conduction by enhanced small polaron hopping and a maximum conductivity of 54 S cm-1 in MnCu0.5Fe0.25Ni0.25CoO4 is achieved at 750 °C. The protective action of the coating applied on 316L stainless steel is evaluated by following the area specific resistance (ASR) of the scale/ coating during heating and cooling cycles. The coating was prepared by screen printing. Post mortem microstructural characterization performed on the both coated samples shows good protection against chromium diffusion.

One approach to increase the energy density of Li-ion batteries is to use high potential cathode material like LiNi0.5Mn1.5O4 (LNMO). However, it suffers from low coulombic efficiency, self-discharge and poor cyclability in carbonates-based electrolytes. Many mechanisms to explain degradation such as HF generation, surface catalytic activity and transition metals dissolution have been suggested to explain these behaviors. By comparison with a non-fluorinated environment, we demonstrated that hydrofluoric acid is not the main reason of capacity loss. A comparison of electrolyte degradation on model thin-film and composite electrodes proved that electrolyte oxidation is catalyzed on the active material surface of LNMO and not on the carbon. A Tafel like behavior of the electrolyte oxidation was obtained thanks to the measure of the steady state current at different potentials. The low coulombic efficiency is essentially related to the self-discharge mechanism. Finally, the capacity fading has been quantitatively correlated to the electrolyte oxidation: at 25 degrees C, about 4% of oxidized electrolyte molecules leads to the degradation of the material, probably due to the dissolution of surface transition metal. By lowering the operating temperature, the electrolyte degradation kinetics decreased, leading proportionally to better cycling stability. Perspectives of this work are also drawn.

The novel bi-molybdate beta-Li0.87Na0.13Cr(MoO4)(2) was prepared by solid state reaction route. Single crystal X-ray diffraction experiment revealed that the compound crystallizes in the triclinic system, in P -1 space group with a = 6.715 (2), b = 7.160 (3), c = 7.237 (1) angstrom, alpha = 91.16 degrees (3), beta = 110.59 degrees (2), gamma = 105.54 degrees (3). Its crystal structure is isotypic to LiCr(MoO4)(2) which has interesting magnetic and electrochemical properties [1-3]. Bond valence sum (BVS) and charge distribution (CHARDI) validation tools supported the structural model. The electrical properties were systematically studied by impedance spectroscopy. The ionic conductivity measurements are performed on pellets of 82% and 87% relative density for LiCr(MoO4)(2) and beta-Li0.87Na0.13Cr(MoO4)(2) respectively. AC impedance spectroscopy studies show that the highest overall conductivity is sigma(326 degrees C) = 7.86 x 10(-7) S cm(-1) Probable diffusion pathways of Li+ ions in the both structures were simulated using the bond valence sum BVS maps method. This analysis shows that the ionic transport in these materials is essentially due to simple hopping of Li+ ions parallel to (101) plane. For beta-Li0.87Na0.13Cr(MoO4)(2) compound, the in-situ High Temperature X-Ray Diffraction (HTXRD), in the temperature range from 25 to 650 degrees C, were also performed and Unit-cell thermal expansion has been discussed. The magnetic study show that these compounds present an antiferromagnetic order below the temperatures T-N = 16 and 30 K for LiCr(MoO4)(2) and beta-Li0.87Na0.13Cr(MoO4)(2) respectively. (C) 2020 Elsevier B.V. All rights reserved.

La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) electrode deposited on Gadolinium Doped Ceria (GDC) has been characterized by cyclic voltammetry and impedance spectroscopy in the temperature range of 300-700 degrees C. We demonstrate that the LSCF microstructure has a strong influence on the shape of the voltammograms and on the variation of the series resistance, R-s, measured on the impedance diagrams as a function of the dc bias. LSCF was deposited with two different microstructures, either porous layer (similar to 10 mu m thick) by screen-printing (SP) or almost dense layer (similar to 2 mu m thick) by Electrostatic Spray Deposition (ESD). For the denser film, one cathodic peak and one reverse anodic peak were evidenced under air at 300 and 500 degrees C. The R-s value was also found to increase with the dc cathodic bias. On the contrary, no peak was observed with the porous film under the same conditions and R-s was independent on the applied potential from 300 to 700 degrees C. Decreasing the oxygen partial pressure allowed the peaks to be evidenced and R-s to vary. The results are discussed in terms of oxygen exchange rate at the LSCF/gas interface, which depends on the LSCF specific surface area and the oxygen partial pressure. (C) 2019 Published by Elsevier Ltd.

In order to increase the energy density of lithium-ion batteries, there are two levels; one is the increase of the specific capacity of both positive and negative active materials (i. e. in Li/S8 technology) and/or the increase of the battery voltage. The most simple solution a promising solution is theo use of positive active materials with high potential (up to 5V vs Li + / Li) [1] because it does not change the technology conception. Among the different materials, The spinel LiNi1/2Mn3/2O4 has a theoretical capacity of 147 mAh/g and a potential of 4.8 V vs Li+/Li, which enable a high energy density [2] (at least 20% more than standard LiCoO2). In the literature, a wide range of values for diffusion coefficient have been reported and only few studies reports values for exchange current density [3,4,5] . This work intended to highlight the impact of thermodynamic factor on the diffusion and to bring new values for the exchange current density, measured by impedance spectroscopy. The study of thin film of spinel LiNi1/2Mn3/2O4 enables to use simplified equations for extracting kinetics and thermodynamics values like exchange current density at the interface of the material, values of the diffusion in the thin electrode and thermodynamic factor that affect the mobility in the structure, depending on the state of charge. These results have then been compared to the ones obtained on composite electrodes. Very and good agreement were obtained even using a 1D model on composite electrodes. [1] Tarascon et al. Nature Mater. 2011 [2] Yi et al. J. Power Sources, 2016 [3] Aurbach et al. Electrochim. Acta, 2005 [4] Amin et al. J. Power Sources, 2017 [5] Nishikawa et al. J. Electroanal. Chem. 2017

Since their market introduction in 1991, lithium (Li)-ion battery is the main solution to power electronic portable devices, and after almost three more decades of development this technology is embedded in modern electric and hybrid cars. However, its maturity leaves little gap to increase its energy density in the order of 250 Wh.kg-1. In order to increase their energy density, a promising solution is to use positive materials with high potential (up to 5V vs Li + / Li) [1] . The spinel LiNi 1/2 Mn 3/2 O 4 which owns a capacity of 147 mAh/g and a potential of 4.8 V vs Li + / Li, enables to reach a high energy density (at least 20% higher than the state of the art Li-ion technology), However, this operating potential is largely above the electrochemical stability range of conventional electrolytes based on carbonate solvents [2] . Cycling tests reveals a low coulombic efficiency induced by electrolyte oxidation and capacity loss induced by material degradation [3] . A simple model based on coulombic efficiency has been developed to quantify the solvent decomposition current. By comparing values obtained on thin film and composite electrode, we proved that the electrolyte oxidation mainly happen on the surface of the LNMO, with a main reaction that can simply be written as: Li + + EC + NMO → EC + + LiNMO where EC stand for a solvent electrolyte molecule and EC+ the product of the solvent oxidation. The rate of solvent decomposition is kinetically controlled by the charge-transfer, therefore a simple anodic Tafel expression has been used to model the current density due to this mechanism and has been compared to our model based on coulombic efficiency. Tests at different C rates indicate that the longer the electrode stays at high potential, the higher is the capacity fading, showing that the product of electrolyte oxidation seems to be involved into material degradation. In order to get a more deep insight into these parasitic reactions (oxidation of the electrolyte, active material degradation), cells were tested at different temperatures (10, 25 and 50°C). Especially, we have obtained that coulombic efficiency is strongly improved when the operation temperature is decreased, in full agreement with thermal activation of the electrolyte decomposition Inter estingly, we obtained a lower capacity fading which demonstrates the strong link between faradic efficiency (electrolyte oxidation) and material degradation. [1] Tarascon et al. Nature Mater. 2011 [2] Yi et al. J. Power Sources, 2016 [3] Pieczonka al. J. of Phys. Chemistry, 2013

In order to increase the energy density of lithium-ion batteries, there are two levels; one is the increase of the specific capacity of both positive and negative active materials (i. e. in Li/S8 technology) and/or the increase of the battery voltage. The most simple solution a promising solution is theo use of positive active materials with high potential (up to 5V vs Li + / Li) [1] because it does not change the technology conception. Among the different materials, The spinel LiNi 1/2 Mn 3/2 O 4 has a theoretical capacity of 147 mAh/g and a potential of 4.8 V vs Li + /Li, which enable a high energy density [2] (at least 20% more than standard LiCoO2). In the literature, a wide range of values for diffusion coefficient have been reported and only few studies reports values for exchange current density [3,4,5] . This work intended to highlight the impact of thermodynamic factor on the diffusion and to bring new values for the exchange current density, measured by impedance spectroscopy. The study of thin film of spinel LiNi 1/2 Mn 3/2 O 4 enables to use simplified equations for extracting kinetics and thermodynamics values like exchange current density at the interface of the material, values of the diffusion in the thin electrode and thermodynamic factor that affect the mobility in the structure, depending on the state of charge. These results have then been compared to the ones obtained on composite electrodes. Very and good agreement were obtained even using a 1D model on composite electrodes. [1] Tarascon et al. Nature Mater. 2011 [2] Yi et al. J. Power Sources, 2016 [3] Aurbach et al. Electrochim. Acta, 2005 [4] Amin et al. J. Power Sources, 2017 [5] Nishikawa et al. J. Electroanal. Chem. 2017

Herein we report the studies of different physical properties (structural, magnetic, thermal, morphologic, electrical, and electrochemical) of two new allotropic β-Na2Ni2M(PO4)3 (NNMP) phosphates, with M = Fe and Al. Pure orthorhombic single-phase powders were prepared under air, using an autocombustion synthesis method. They crystallize in the orthorhombic Imma space group with similar unit cell parameters [a = 10.1592(2), b = 13.0321(3), c = 6.4864(2) Å] and [a = 10.3993(1), b = 13.1966(1), c = 6.4955(1) Å] for β-Na2Ni2M(PO4)3 (NNAP) and β-Na2Ni2Fe(PO4)3 (NNFP), respectively. Crystal structures of both compounds were determined using X-ray powder diffraction and Rietveld method refinements, which indicate the occurrence of Ni2+ in the 8g site, and of M3+ in the 4a site of the structure. The structure consists of a three-dimensional anionic framework obtained by the association on MO6, NiO6, and PO4 polyhedra, sharing edges and corners. The resulting three-dimensional structure creates monodimensional channels along the [100] and [010] directions formed by face-shared oxygen polyhedra and occupied by Na+ cations. This nondisordered cationic distribution is confirmed by a significant change of magnetic properties. Thus, both NNAP and NNFP samples show paramagnetic to ferromagnetic transition at 14 and 19 K, respectively. For the two compounds, thermal stability, electrical conductivity, and electrochemical properties have been also investigated. The intercalation/desintercalation properties of NNMP compounds as positive electrode were tested in sodium-ion batteries. The first cycling curves exhibit a significant polarization for both prepared samples.

The kinetic of LiFePO4 chemical delithiation was studied on sintered powders synthesized by precipitation method and partially oxidized using Br2 in acetonitrile. Thorough X-ray diffraction analyses using Rietveld refinements revealed a two-phase reaction with a slight deviation of the lattice parameters. Coherency domains of the two end members were determined using the Thomson-Cox-Hasting function and they linearly increase for the lithium-poor phase at the detriment of the lithium-rich phase. The HRSTEM-EELS measurements on partially delithiated samples validate the Shrinking Core mechanism with a core of LiFePO4 surrounded by a shell of FePO4. Thus, each particle undergoes a two-phased transformation. Furthermore, the HRSTEM-EELS reveals that the grain boundaries (resulting from the heat treatment in order to improve phase crystallinity) strongly hinder the delithiation kinetics. Chemical delithiation triggers agglomerates breaking and particle splitting at grain boundaries. This new aspect may provide information on the impact of microstructure on the electrochemical performances of LiFePO4 materials.

Herein we report the studies of different physical properties (structural, magnetic, morphologic, electrical and electrochemical) of NaNi1/3Mn1/3Co1/3-xFexO2 compounds with x = 0; 0.111; 0.222; 0.333. Pure single-phase powders were prepared under air, using solid state synthesis method. Unit cell parameters of various compounds were refined using X-ray powder diffraction data in O3-type crystal structure and R-3m space group. For all the compounds, magnetic, electrical and electrochemical properties have been also investigated. Temperature dependence of magnetic susceptibilities showed the Curie-Weiss behaviors for all compounds, and a significant change of magnetic property from antiferro- to ferromagnetic comportment with iron substitution. The magnetic hysteresis M(H) loops indicated an increasing saturation magnetization from x = 0 to 0.333. The electrical and electrochemical studies of the four samples also revealed enhanced polarization behavior with the substitution rate of iron.

The LiFePO4 and FePO4 compounds were synthesized by coprecipitation method. The X-ray diffraction and magnetic measurements were used to determine the crystal structure and to investigate the magnetic properties, respectively. From theoretical investigation point of view, self-consistent ab initio calculations, based on Density Functional Theory approach and using Full Potential linearized Augmented Plane Wave (FLAPW) method, were performed to investigate both electronic and magnetic properties of the LiFePO4. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Fe plans. Magnetic moments considered to lie along (010) axes are computed. In addition, average equilibrium voltage over a full cycle (Vcell) of the LiFePO4 battery is estimated from our FLAPW calculations. Computed magnetic moments are used as input for the high temperature series expansion (HTSE) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe–Fe and Fe–O–Fe in LiFePO4 are obtained using the mean field theory. The Néel temperature and critical exponent associated with the magnetic susceptibility are obtained employing HTSEs. The obtained inverse magnetic susceptibility is revealed in good accordance with our experimental data.

Olivine LiFePO4 (de)lithiation mechanism has been largely studied over the past 10 years and is usually observed and interpreted as a two-phase transition. However, recent publications demonstrated that the dynamic transformation from LiFePO4 to FePO4 (and reverse) would go through a metastable solid solution LixFePO4, especially in the case nanoparticles at high charging rate [1-3]. Olivine NaFePO4 (de)sodiation mechanism appears even more complex with the existence of the intermediate phase Na2/3FePO4, leading to two charging plateaus and extended solubility limits [4-6]. This work presents the peculiar (de)insertion mechanism during chemical delithiation and electrochemical sodiation observed by operando XRD. Firstly, ex situ XRD performed on partially chemically delithiated LixFePO4 powders have shown a stabilized solid solution at equilibrium state, which is usually observed under dynamic conditions [3]. Secondly, the Li0,6FePO4 phase obtained by chemical delithiation has been electrochemically characterized in Na half-cell. Associated operando XRD displays a progressive shift of the diffraction peaks (Figure 1), revealing a Li + /Na + co-insertion mechanism via a complete solid solution. These results, reported for the first time, bring new insights on Li + /Na + insertion mechanisms within olivine FePO4 structure.

Electrospun carbon nanofibres (CNFs) containing CNTs were produced by electrospinning and subsequent thermal treatment. This material was evaluated as a bioelectrode for biofuel cell applications after covalent grafting of laccase. Bis-pyrene-modified ABTS was used as a plug to wire laccase to the nanofibres leading to a maximum current density of 100 μA cm(-2).