Institut des Matériaux Jean Rouxel

International audience

Electrochemical capacitors, so-called supercapacitors, play an important role in energy storage and conversion systems.

The methodology presented within this work is a result of years of interactions between many junior and senior X-ray Photoelectron Spectroscopy (XPS) users operating within the CasaXPS spectral processing and interpretation program framework. In particular, discussions arising from a series of workshops have been a significant source for developing the overall XPS data processing concept and are the motivation for creating this work. These workshops organized by the Institut des Matériaux Jean Rouxel (IMN), Nantes gather both experienced and novice users of XPS for a week of discourse in conceptual experiment design and the resulting data processing. However, the framework constructed and utilized within these workshops encouraged the dissemination of knowledge beyond XPS data analysis and emphasized the importance of a multi-disciplinary collaborative approach to surface analysis problem-solving. The material presented here embodies data treatment originating from data made available to the first CNRS Thematic Workshop presented at Roscoff 2013. The methodology described here has evolved over the subsequent workshops in 2016 and 2019 and currently represents the philosophy used in CasaXPS spectral data processing paradigm.

The current interest in ionic liquids (ILs) is motivated by some unique properties, such as negligible vapour pressure, thermal stability and non-flammability, combined with high ionic conductivity and wide electrochemical stability window. However, for material applications, there is a challenging need for immobilizing ILs in solid devices, while keeping their specific properties. In this critical review, ionogels are presented as a new class of hybrid materials, in which the properties of the IL are hybridized with those of another component, which may be organic (low molecular weight gelator, (bio)polymer), inorganic (e.g. carbon nanotubes, silica etc.) or hybrid organic-inorganic (e.g. polymer and inorganic fillers). Actually, ILs act as structuring media during the formation of inorganic ionogels, their intrinsic organization and physicochemical properties influencing the building of the solid host network. Conversely, some effects of confinement can modify some properties of the guest IL, even though liquid-like dynamics and ion mobility are preserved. Ionogels, which keep the main properties of ILs except outflow, while allowing easy shaping, considerably enlarge the array of applications of ILs. Thus, they form a promising family of solid electrolyte membranes, which gives access to all-solid devices, a topical industrial challenge in domains such as lithium batteries, fuel cells and dye-sensitized solar cells. Replacing conventional media, organic solvents in lithium batteries or water in proton-exchange-membrane fuel cells (PEMFC), by low-vapour-pressure and non flammable ILs presents major advantages such as improved safety and a higher operating temperature range. Implementation of ILs in separation techniques, where they benefit from huge advantages as well, relies again on the development of supported IL membranes such as ionogels. Moreover, functionalization of ionogels can be achieved both by incorporation of organic functions in the solid matrix, and by encapsulation of molecular species (from metal complexes to enzymes) in the immobilized IL phase, which opens new routes for designing advanced materials, especially (bio)catalytic membranes, sensors and drug release systems (194 references).

As the world moves toward electromobility and a concomitant decarbonization of its electrical supply, modern society is also entering a so-called fourth industrial revolution marked by a boom of electronic devices and digital technologies. Consequently, battery demand has exploded along with the need for ores and metals to fabricate them. Starting from such a critical analysis and integrating robust structural data, this review aims at pointing out there is room to promote organic-based electrochemical energy storage. Combined with recycling solutions, redox-active organic species could decrease the pressure on inorganic compounds and offer valid options in terms of environmental footprint and possible disruptive chemistries to meet the energy storage needs of both today and tomorrow. We review state-of-the-art developments in organic batteries, current challenges, and prospects, and we discuss the fundamental principles that govern the reversible chemistry of organic structures. We provide a comprehensive overview of all reported cell configurations that involve electroactive organic compounds working either in the solid state or in solution for aqueous or nonaqueous electrolytes. These configurations include alkali (Li/Na/K) and multivalent (Mg, Zn)-based electrolytes for conventional "sealed" batteries and redox-flow systems. We also highlight the most promising systems based on such various chemistries relying on appropriate metrics such as operation voltage, specific capacity, specific energy, or cycle life to assess the performances of electrodes.

We present a comparative vibrational study of leucoemeraldine, emeraldine, and pernigraniline bases: fully reduced, half oxidized, and fully oxidized forms of polyaniline, respectively. By performing a general vibrational calculation based on the symmetrized dynamical matrix, we determine the force constants, the potential-energy distribution, and the Cartesian displacements for the three forms of polyaniline and associated model compounds. We discuss the assignment of the fundamental Raman and ir vibrational modes of the polymers. The modifications of the frequencies and consequently of the main force constants observed from one compound to the other are analyzed by considering the quinoid and aromatic characters along the chain. In this way, we determine a force field with physical significance which may be used to interpret the electronic modification between neutral and protonated as well as photoexcited emeraldine forms. This comparative analysis demonstrates the important changes of the electronic distribution around the nitrogen atom, which plays a major role in the conduction mechanism in this class of conducting polymers.

Using a new electrolyte composition, which is stable against oxidation up to 5 V, the full electrochemical deintercalation of lithium from the spinel is studied. The origin of two new reversible oxidation‐reduction peaks near 4.5 and 4.9 V are examined. The capacity associated with these peaks depends on both the nominal composition in and the synthesis conditions (annealing temperatures and cooling rates), and thereby can be used as an indicator for electrochemically optimized powders. We present evidence that these peaks are related to local structural defects. Thermogravimetric measurements (TGA) on powders show a reversible loss of oxygen that can reach 5% at 1000°C. We find that some of this weight loss is associated with the conversion of cubic to a new tetragonal spinel phase and then to the decomposition of this phase into the orthorhombic phase plus other products. This new tetragonal spinel is prepared as a single phase, and its electrochemical properties are reported.

The vibrational properties of poly(3,4-ethylenedioxythiophene) (PEDT) have been studied by means of UV−vis−NIR optical absorption spectroscopy and resonance Raman scattering (RRS) spectroscopy with two excitation lines: green (514 nm) and infrared (1064 nm). The two-step oxidative doping process does not induce a drastic change for the Raman bands, but the changes that occur are clearly evidenced. During doping, new bands appear, indicating a modification of the electronic structure of the polymer. Vibrational calculations were carried out using a symmetrized dynamical matrix model and the results were compared with experimental data, especially in the 1200−1600 cm-1 range, where the CαCβ and Cβ−Cβ stretching vibrations are active. It appears that PEDT seems to have an intermediate electronic structure, between the quinoid and benzoid structures.

The existing mechanisms proposed to explain the phosphorescence of SrAl2O4:Eu2+,Dy3+ and related phosphors were found to be inconsistent with a number of important experimental and theoretical observations. We formulated a new mechanism of phosphorescence on the basis of the facts that the d orbitals of Eu2+ are located near the conduction band bottom of SrAl2O4, that the Eu2+ concentration decreases during UV excitation, and that trace amounts of Eu3+ are always present in these phosphors. In our mechanism, some Eu2+ ions are oxidized to Eu3+ under UV, and the released electrons are trapped at the oxygen vacancy levels located in the vicinity of the photogenerated Eu3+ cations. The phosphorescence arises from the recombination of these trapped electrons around the photogenerated Eu3+ sites with emission at 520 nm. The codopant Dy3+ enhances the phosphorescence by increasing the number and the depth of electron traps, and the codopant B3+ enhances the phosphorescence by increasing the depth of electron traps. We also probed the origin of another emission at 450 nm of SrAl2O4:Eu2+ that occurs at low temperatures. Our analysis indicates that this emission is caused by a charge transfer from oxygen to Eu3+ cations and is associated with a hole trapping.

Cellulosic colloidal nanorods of different origins were used in order to investigate the effect of various elongated shapes adsorbed at the oil–water interface for Pickering emulsion characteristics. Nanocrystals of length ranging from 185 nm to 4 μm were obtained from the hydrolysis of cellulose microfibrils of three different biological origins: cotton (CCN), bacterial cellulose (BCN) and Cladophora (ClaCN) leading to aspect ratios ranging from 13 to 160. These nanocrystals are irreversibly adsorbed at the oil–water interface and form ultrastable emulsions. Individual droplets of similar diameter were obtained under diluted conditions, illustrating both similar wetting properties and nanocrystal flexibility for the three different types of nanocrystals. However, it was shown that the aspect ratio directly influences the coverage ratio giving rise, on the one hand to a dense organisation (coverage >80%) with short nanocrystals and on the other hand to an interconnected network of low covered droplets (40%) when longer nanocrystals are used. An estimation is made showing that for the longer nanocrystals, 55% of the nanocrystals introduced are involved in the network of the material. The capillary force that promotes attractive interactions between nanocrystals was also addressed. These results lead to a better understanding of the adsorption process for rod-like particles of various aspect ratios for the elaboration of a controlled surface architecture, from a homogeneous monolayer to interconnected porous multilayered interfaces.

The use of peak fitting to extract information from x-ray photoelectron spectroscopy (XPS) data is of growing use and importance. Due to increased instrument accessibility and reliability, the use of XPS instrumentation has significantly increased around the world. However, the increased use has not been matched by the expertise of the new users, and the erroneous application of curve fitting has contributed to ambiguity and confusion in parts of the literature. This guide discusses the physics and chemistry involved in generating XPS spectra, describes good practices for peak fitting, and provides examples of appropriate use along with tools for avoiding mistakes.

International audience

A new polyaniline/multi-wall carbon nanotube (PANI/MWNT) composite has been successfully synthesized by an “in-situ” polymerisation process; Raman studies indicate a site-selective interaction between the quinoid ring of the polymer and the MWNTs opening the way for charge transfer processes; transport measurements clearly reveal drastic changes in the electronic behaviour confirming the formation of a true composite material with enhanced electronic properties.

Carbon nanohorns (sometimes also known as nanocones) are conical carbon nanostructures constructed from an sp(2) carbon sheet. Nanohorns require no metal catalyst in their synthesis, and can be produced in industrial quantities. They provide a realistic and useful alternative to carbon nanotubes, and possibly graphene, in a wide range of applications. They also have their own unique behavior due to their specific conical morphology. However, their research and development has been slowed by several factors, notably during synthesis, they aggregate into spherical clusters ∼100 nm in diameter, blocking functionalization and treatment of individual nanocones. This limitation has recently been overcome with a new approach to separating these "dahlia-like" clusters into individual nanocones. In this review, we describe the structure, synthesis, and topology of carbon nanohorns, and provide a detailed review of nanohorn chemistry.

The potential distribution through plastic Li‐ion cells during electrochemical testing was monitored by means of three‐ or four‐electrode measurements in order to determine the origin of the poor electrochemical performance (namely, premature cell failure, poor storage performance in the discharged state) of /C Li‐ion cells encountered at 55°C. Several approaches to insert reliably one or two reference electrodes that can be either metallic lithium or an insertion compound such as into plastic Li‐ion batteries are reported. Using a reference electrode, information regarding the evolution of (i) the state of charge of each electrode within a Li‐ion cell, (ii) their polarization, and (iii) their rate capability can be obtained. From these three‐electrode electrochemical measurements, coupled with chemical analyses, X‐ray diffraction, and microscopy studies, one unambiguously concludes that the poor 55°C performance is mainly due to the instability of the phase toward Mn dissolution in ‐type electrolytes. A mechanism, based on Mn dissolution, is proposed to account for the poor storage performance of /C Li‐ion cells.

The fabrication of miniaturized electrochemical energy storage systems is essential for the development of future electronic devices for Internet of Thing applications. This paper aims at reviewing the current micro-supercapacitor technologies and at defining the guidelines to produce high performance micro-devices with special focuses onto the 3D designs as well as the fabrication of solid state miniaturized devices to solve the packaging issue.

The phase diagram of the organic superconductor kappa-(ET)2Cu[N(CN)2]Cl has been accurately measured from 1H NMR and ac susceptibility techniques under helium gas pressure. The domains of stability of antiferromagnetic and superconducting orders in the pressure vs temperature plane have been determined. Both phases overlap through a first-order boundary that separates two regions of inhomogeneous phase coexistence. The boundary curve merges with the first-order line of the metal-insulator transition which ends with a critical point at higher temperature. The whole phase diagram features a point-like region where metallic, insulating, antiferromagnetic, and non-s-wave superconducting phases all meet.

Cu2ZnSnS4 (CZTS) is an interesting material for sustainable photovoltaics, but efficiencies are limited by the low open-circuit voltage. A possible cause of this is disorder among the Cu and Zn cations, a phenomenon which is difficult to detect by standard techniques. We show that this issue can be overcome using near-resonant Raman scattering, which lets us estimate a critical temperature of 533 ± 10 K for the transition between ordered and disordered CZTS. These findings have deep significance for the synthesis of high-quality material, and pave the way for quantitative investigation of the impact of disorder on the performance of CZTS-based solar cells.

Understanding the failure mechanism of silicon based negative electrodes for lithium ion batteries is essential for solving the problem of low coulombic efficiency and capacity fading on cycling and to further implement this new very energetic material in commercial cells. To reach this goal, several techniques are used here: post mortem7Li MAS NMR and SEM, electrochemical impedance spectroscopy (EIS) and three-electrode-based electrochemical analysis. 7Li MAS NMR analyses of the charged batteries demonstrate that the major part of the lithium lost during the charge of batteries is not trapped in LixSi alloys but instead at the surface of the Si particles, likely as a degradation product of the liquid electrolyte. Observed by SEM, a dead electrode has a thick “SEI” layer at its surface. EIS and incremental capacity analyses demonstrate that the growth of this layer is responsible for the failure of the electrode through a continuous decrease of its active surface area associated with a rise of the electrode polarization. It is demonstrated that the main cause of capacity fade of Si-based negative electrodes is the liquid electrolyte degradation in the case of nano Si-particles formulated with the carboxymethyl cellulose (CMC) binder. This degradation results in the formation of a blocking layer on the active mass, which further inhibits lithium diffusion through the composite electrode.

Abstract The aim of the present contribution is to give a review on the recent work concerning Cd‐free buffer and window layers in chalcopyrite solar cells using various deposition techniques as well as on their adaptation to chalcopyrite‐type absorbers such as Cu(In,Ga)Se 2 , CuInS 2 , or Cu(In,Ga)(S,Se) 2 . The corresponding solar‐cell performances, the expected technological problems, and current attempts for their commercialization will be discussed. The most important deposition techniques developed in this paper are chemical bath deposition, atomic layer deposition, ILGAR deposition, evaporation, and spray deposition. These deposition methods were employed essentially for buffers based on the following three materials: In 2 S 3 , ZnS, Zn 1 − x Mg x O. Copyright © 2010 John Wiley & Sons, Ltd.