Multidisciplinary investigation on cold seeps with vigorous gas emissions in the Sea of Marmara (MarsiteCruise): Strategy for site detection and sampling and first scientific outcome

MarsiteCruise was undertaken in October/November 2014 in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the collected gas bubbles. The in situ Raman spectroscopy was used as a decision-making tool to evaluate the need for continuing with the sampling of gases from the discovered seep, or to move to another one. Push cores were gathered to study buried carbonates and pore waters at the surficial sediment, while CTD-Rosette allowed collecting samples to measure dissolved-methane concentration within the water column followed by a comparison with measurements from samples collected with the submersible Nautile during the Marnaut cruise in 2007. Overall, the visited sites were characterized by a wide diversity of seeps. CO2- and oil-rich seeps were found at the westernmost part of the sea in the Tekirdag Basin, while amphipods, anemones and coral populated the sites visited at the easternmost part in the Cinarcik Basin. Methane-derived authigenic carbonates and bacterial mats were widespread on the seafloor at all sites with variable size and distributions. The measured methane concentrations in the water column were up to 377 μmol, and the dissolved pore-water profiles indicated the occurrence of sulfate depleting processes accompanied with carbonate precipitation. The pore-water profiles display evidence of biogeochemical transformations leading to the fast depletion of seawater sulfate within the first 25-cm depth of the sediment. These results show that the North Anatolian Fault and inherited faults are important migration paths for fluids for which a significant part is discharged into the water column, contributing to the increase of methane concentration at the bottom seawater and favoring the development of specific ecosystems

Raman and FTIR Spectroscopy investigations of carbon-coated LixFePO4 materials

Raman and Fourier transform infrared (FTIR) spectroscopy investigations were performed on carbon-coated LiFePO4 materials differing by the temperature of their thermal treatments (575 and 800°C) and by their electrochemical performance, with that obtained at a higher temperature showing larger reversible capacity and better capacity retention at high rates. Raman spectra gave information on the carbon located at the surface of the LiFePO4 particles, which was shown for the two samples to be highly disordered with small in-plane correlation lengths (<3 nm). A UV Raman study has shown that these carbon coatings contain almost no sp3-type carbon hybridization. This study has also highlighted again that the sp3-type C/sp2-type C ratio cannot be determined straightforwardly from Raman spectra recorded with visible excitation (such as 632.8 nm), and thus that no direct correlation can be done between the Raman band intensity ratio ID/IG and the sp3-type C/sp2-type C ratio; a UV Raman study is necessary to get the true information on the sp3-type C contribution. The baseline and absolute intensity of the FTIR spectra were shown to be sensitive to changes in the electronic conductivity of the C-LiFePO4 samples. Furthermore, good crystallinity was maintained for LixFePO4 materials upon cycling, showing good reversibility of the lithium deintercalation/intercalation reaction

Spinel materials for Li-ion batteries: new insights obtained by operando neutron and synchrotron X-ray diffraction

International audienceIn the last few decades Li-ion batteries changed the way we store energy, becoming a key element of our everyday life. Their continuous improvement is tightly bound to the understanding of lithium (de)intercalation phenomena in electrode materials. Here we address the use of operando diffraction techniques to understand these mechanisms. We focus on powerful probes such as neutrons and synchrotron X-ray radiation, which have become increasingly familiar to the electrochemical community. After discussing the general benefits (and drawbacks) of these characterization techniques and the work of customization required to adapt standard electrochemical cells to an operando diffraction experiment, we highlight several very recent results. We concentrate on important electrode materials such as the spinels Li1 + xMn2 − xO4 (0 ≤ x ≤ 0.10) and LiNi0.4Mn1.6O4. Thorough investigations led by operando neutron powder diffraction demonstrated that neutrons are highly sensitive to structural parameters that cannot be captured by other means (for example, atomic Debye–Waller factors and lithium site occupancy). Synchrotron radiation X-ray powder diffraction reveals how LiMn2O4 is subject to irreversibility upon the first electrochemical cycle, resulting in severe Bragg peak broadening. Even more interestingly, we show for the first time an ordering scheme of the elusive composition Li0.5Mn2O4, through the coexistence of Mn3+:Mn4+ 1:3 cation ordering and lithium/vacancy ordering. More accurately written as Li0.5Mn3+0.5Mn4+1.5O4, this intermediate phase loses the [Fd\overline 3m] symmetry, to be correctly described in the P213 space group

New spinel cobalt oxides, potential conductive additives for the positive electrode of Ni-MH batteries

Temperature plays a key role in the formation of the cobalt-based conductive network at the positive electrode of alkaline batteries during the first charge. Electrodes pasted with CoO were oxidized in various concentrated alkaline media, in order to understand the phenomena involved. In these conditions, the experiments show the formation of a Co3O4 type phase with defects. The presence of lithium in the electrolyte is proven to play an important role in the conductivity of the synthesized phases. Especially in 2.5 M LiOH, a pure phase is isolated that has a spinel structure close to Co3O4 but containing H and Li. This phase is shown to be a good conductor and is also observed in (KOH, NaOH, LiOH) ternary industrial electrolyte. It could hence take part to the improvement of the properties of nickel electrodes observed when the beginning of the first charge is performed at high temperature

A new null matrix electrochemical cell for Rietveld refinements of in-situ or operando neutron powder diffraction data

In-situ techniques proved to be exceptionally useful tools to understand electrode materials for Li-ion batteries but in-situ neutron diffraction (ND) during battery operation knew a slow development, due to the intrinsic difficulties it held. We have designed a new electrochemical cell, manufactured with a completely neutron-transparent (Ti,Zr) alloy. Such a cell is able to combine, for the first time, good electrochemical properties and the ability to collect neutron diffraction patterns operando, with good statistics and no other Bragg peaks than those of the electrode material of interest. This allows detailed structural determinations of electrode materials by Rietveld refinement during operation. First case studies hereby reported are the olivine LiFePO4 and the overstoichiometric spinel Li1.1Mn1.9O4, investigated at the D20 diffractometer of ILL (Grenoble), and compared to pure powder patterns obtained from the high-resolution D2B diffractometer. These studies demonstrate the feasibility and reliability of such experiments and open the field to a wide range of investigations on battery electrode materials

Unravelling the morphological dependency of the LiNi0.6Mn0.2Co0.2O2 layered oxide reactivity in Li-ion batteries

International audienceLiNi0.6Mn0.2Co0.2O2 is one of the most promising positive electrode material for Li-ion batteries. Platelet-shaped particles of 17 nm and 86 nm thickness were obtained, with the required composition and a structure close to the ideal 2D layered structure (less than 5.2% Ni2+ ions in Li+ sites). The electrochemical performances and surface reactivity of the materials were characterized in Li-ion batteries and compared to that of 280 nm particles with a more conventional morphology. Post-cycling analyses revealed a particular reactivity at high potential for the platelets compared to the conventional particles. X-Ray photoelectron spectroscopy and ex situ XRD analyses were performed to characterize the composition of the positive electrode/electrolyte interface and the structural changes undergone by the three materials upon cycling respectively. This study showed that, as well as the particles’ composition, their morphology plays a significant role regarding the reactivity and the structural changes occurring during cycling at high potential

How the physicochemical and structural properties of globular proteins affect their behavior at the air-solution interface and their foaming properties

We have been studying the behavior of several globular food proteins at the air-solution interface and their capacity to stabilize aqueous foams. Our aim is to understand the relation of foaming ability to the properties of the adsorbed protein layer, and to understand the relation of the properties of the adsorbed protein layer to the structural and physicochemical characteristics of the adsorbed protein(s). We used a combination of techniques providing insight in the adsorption kinetics (ellipsometry, surface tension), in the interfacial shear rheology and in the molecular conformational rearrangements of adsorbed proteins (polarization-modulation infrared reflection-absorption spectroscopy, PM-IRRAS). We compared proteins with distinctive molecular features, native and chemically or physically modified forms of one protein, and studied the interfacial behavior of proteins in binary solutions. We found that depending on the physicochemical adsorption conditions, different proteins form qualitatively different interfacial layer, as regards monolayer or multilayer adsorption, or the interfacial shear rheology. Strikingly, very minor structural modifications prior to adsorption to the air-solution interface could lead to dramatic changes in the interfacial behavior, in parallel to dramatic changes in the foaming ability. We also showed that in the case of binary solutions of oppositely charged proteins, a clear co-adsorption occurs, leading to very high surface concentrations and to deeply modified interfacial film properties, which cannot be extrapolated from the addition of individual behaviors. In addition, preliminary results about the osmotic pressure of bulk, very highly concentrated protein solutions suggest that in interfacial studies, due to the protein crowding close to the interface, intermolecular interactions could be of prominent importance in the understanding of interfacial properties

High rate performance for carbon‐coated Na3V2(PO4)2F3 in Na‐Ion Batteries

The electrochemical and structural properties of a series of three different Na3V2(PO4)2F3 samples (with or without carbon coatings of different natures), obtained via different synthesis methods, are compared through operando high‐resolution synchrotron X‐ray diffraction. The pristine materials all possess negligible quantities of oxygen defects, as probed by the b/a lattice parameters ratios and solid‐state NMR. Operando X‐ray diffraction recorded during charge at C/2 reveals subtle differences between the samples (of different particle size, morphology, and carbon‐coating nature) in the crystallinity of the intermediate compositions formed within the Na3V2(PO4)2F3–NaV2(PO4)2F3 phase diagram. A new temperature‐controlled operando cell is used to determine this phase diagram at 0 °C, mostly unchanged compared to that of recorded at 25 °C. Very high charging and discharging rates are demonstrated and intermediate compositions can be spotted operando even up to 25 C rate at which the compositional phase diagram is only slightly altered compared to that recorded under equilibrium conditions. Optimized carbon‐coated Na3V2(PO4)2F3 shows exceptional rate and electrochemical cycling capabilities, as demonstrated by hard carbon//Na3V2(PO4)2F3 18650 prototypes of 75 Wh kg−1 that can be charged or discharged 4000 times at 1 C rate.Batteries à ions sodium pour des robots télécommandésLaboratory of excellency for electrochemical energy storag

Evidence and age estimation of mass wasting at the distal lobe of the Congo deep-sea fan

International audienceOn continental margins, sulfate reduction occurs within the sedimentary column. It is coupled with the degradation of organic matter and the anaerobic oxidation of methane. These processes may be significantly disturbed by sedimentary events, leading to transient state profiles for the involved chemical species. Yet, little is known about the impact of turbidity currents and mass wasting on the migration of chemical species and the redox reactions in which they are involved. Due to its connection to the River, the Congo deep-sea fan continuously receives huge amount of organic matter-rich sediments primarily transported by turbidity currents, which impact on the development of the associated ecosystems (Rabouille et al., 2016). Thus, it is well suited to better understand causal relationships between sedimentary events and fluid flow path, with consequences on the zonation of early diagenesis sequences. Here, we combined sedimentological observations with geochemical analyses of pore-water and sediment samples to explore how sedimentary instabilities affected the migration of methane and the distribution of organic matter within the sedimentary column. The results unveiled mass wasting processes affecting recent turbiditic and pelagic deposits, and are interpreted as being slides/ slumps and debrites. Two slides were responsible for the exhumation of an organic matter-rich sedimentary block of more than 5 m thick and the movement of a methane-rich sedimentary block, while turbidity currents enable the intercalation of sandy intervals within a pelagic clay layer. The youngest slide promoted the development of two Sulfate Methane Transition Zones (SMTZ), and may have possibly triggered a lateral migration of methane. Numerical simulation of the sulfate profile indicates that the youngest sedimentary event has occurred around a century ago. Our study emphasizes that turbidity currents and sedimentary instabilities can significantly affect the transport paths and the distribution of both methane and organic matter in the terminal lobe complex, with consequences on geochemical zonation of the sequential early diagenetic processes within the sedimentary column