Search

International audience; We propose here a new method to functionalize carbon materials via a catalyzed Diels–Alder reaction. In a Diels–Alder reaction, carbon materials can be used as a diene or a dienophile. Here, carbon materials are used as dienes and alkyne-terminated derivatives as dienophiles. Different carbon materials, i.e., glassy carbon, carbon powder (carbon black), pyrolytic graphite carbon materials, and graphene, were functionalized by alkyne ferrocene derivatives or perfluoro-tagged alkyne molecules and characterized by electrochemical means, atomic force microscopy, and X-ray photoelectron spectroscopy experiments. This method allows for the rapid functionalization of carbon materials in mild conditions with high surface coverage.

Marennine has long been known as the unique peculiar pigment responsible for the natural greening of oysters. It is specifically produced by the marine diatom Haslea ostrearia and it is a natural blue molecule indeed promising for food industry because of the rarity of such non-toxic, blue-colored pigments. In the search for its still not defined molecular structure, investigation of the color changes with the redox state has been carried out combining different approaches. Reducing and oxidizing chemicals have been added to purified marennine solutions and a stable blue-green color has been confirmed for the oxidized state, while a yellow color corresponded to the reduced unstable state. Raman spectroscopy has been used to monitor changes in the Raman spectra corresponding to the different colored states, and cyclic voltammetry has allowed the detection of a redox system in which protons and electrons are exchanged. These findings show that marennine is a suitable stable blue pigment for use in food applications and help in the elucidation of the chromophore structure.

International audience; Depuis plus de deux décennies, une stratégie pour améliorer les performances des supercondensateurs carbonés consiste à incorporer aux matériaux capacitifs des fonctions redox qui sont le lieu d’échanges électroniques. De cette façon, la charge faradique stockée au niveau des molécules s’ajoute à la capacité de double couche électrochimique du carbone. Pour que la contribution des molécules au stockage électrochimique de la charge soit optimale, il est important de réduire l’impact des molécules sur la texture des carbones activés pour qu’une plus grande surface des micropores reste accessible aux ions de l’électrolyte après modification. En absence de contrôle du greffage, l’introduction d’une faible quantité de molécules s’accompagne d’une perte importante de la surface microporeuse qui contribue le plus efficacement à la capacité de double couche électrochimique. Dans ce travail, des alternatives au greffage du carbone sont proposées pour améliorer l’intégration des molécules. Une première stratégie consiste à utiliser le liant polymère comme plateforme pour le greffage et dans une deuxième approche, l’impact de la modification chimique sur la texture du carbone est réduit en limitant le greffage au dépôt d’une monocouche. Dans cette dernière approche, le carbone activé Norit S50 a été modifié par réaction spontanée avec des sels de diazonium et le greffage des molécules a été contrôlé par la stratégie de «protection/déprotection» récemment publiée par P. Hapiot et Y. Leroux. Nous montrerons que la stratégie de «protection/déprotection» du sel de diazonium permet également d’ajuster les dimensions de la molécule au diamètre moyen des pores du carbone en modulant l’encombrement stérique du groupement protecteur, permettant de généraliser cette approche à des carbones de textures différentes.

International audience

International audience

International audience

International audience

International audience

National audience

International audience; Robust attachment of functional molecules is of increasing interest for tuning the surface properties of a large variety of substrates for applications in energy, environment, and biology. For specific applications, such as electronic organic, a well-ordered deposit is requisite. Unfortunately, the chemical derivatization procedures giving a covalent linkage with the surface often produce disordered multilayers. Here, we report on the attachment of a pi-conjugated aminoferrocene derivative by the oxidation of the amino group assisted by the ferrocene moiety. Comparison of saturated and delocalized bridges between the amino and ferrocene groups, shows that the pi-conjugation improves the electric contact between the ferrocene and the amine, allowing the amine to be indirectly oxidized through an intra-molecular electron transfer after oxidation of the ferrocene part when an unsaturated bridge exists. Results show that the properties of the organic deposit differ depending on whether the electrode derivatization is achieved by direct oxidation of the amine or via the oxidation of the ferrocene group. Based on electrochemistry, AFM, quartz microbalance and XPS results, mechanisms for the surface derivatization are discussed.

International audience; Activated carbons are attractive materials for supercapacitors due to their high specific surface area. A proper selection of activated carbons allows reaching a capacitance of several hundred farads per gram in aqueous electrolytes. To exceed this value, a faradaic contribution to the charge storage can be added to the purely capacitive process by grafting redox molecules. However, the grafting of molecules is often accompanied by a decrease of the intrinsic performance of the carbon, such as the double-layer capacitance. Practically, because carbon powder cannot be used alone to fabricate an electrode, carbon particles are commonly mixed with an organic binder and a conductive additive, such as carbon black, to obtain a carbon paste with suitable mechanical and electrical properties. In such composite electrode, the binder does not contribute to the charge storage process and reduces the gravimetric capacitance. One approach for improving the performances without decreasing the double-layer capacitance contribution of the carbon is to use the binder for the charge storage by grafting molecules onto its polymeric skeleton. In this way, the redox binder is expected to have the dual functionality of both the binder and the active material. Here, this original approach is illustrated with a modified binder prepared by reaction between in situ generated diazonium ions and polystyrene. The charge storage properties of the electrode based on the modified binder are compared to those of an electrode based on modified carbon powder to demonstrate the potentiality of such redox active binder

National audience

National audience; Depuis plus de deux décennies, les dispositifs de stockage électrochimiques de l’électricité ont entamé leur révolution organique. Pseudo-supercondensateurs, supercondensateurs redox et dispositifs hybrides "tout organiques" ont déjà conquis les communautés scientifique et industrielle, même si des efforts importants restent à faire pour améliorer leurs performances et leur stabilité afin de pourvoir les intégrer de manière permanente à des structures de longue durée de vie (aéronautique, automobile, bâtiment, etc…). Une stratégie récente consiste à greffer de petites molécules électroactives à la surface de carbones activés. L’assemblage de ces éléments génériques hautement modulables conduit à un très grand nombre de combinaisons possibles et des règles doivent être respectées pour que le greffage soit bénéfique. Ce travail présente les apports et les limitations de la stratégie du greffage, et se conclut sur une alternative originale au greffage des molécules sur le carbone. L’utilisation d’un liant polymère comme plateforme pour le greffage d’unités catéchol semble être une alternative prometteuse au greffage du carbone, puisqu’il permet de réconcilier la molécule et le carbone en maintenant une bonne capacité spécifique totale, une plus grande surface accessible aux ions de l’électrolyte et une faible résistance au transport des ions dans la porosité du carbone.

International audience

International audience

International audience

International audience

International audience; Activated carbons are attractive materials for supercapacitors due to their physical and chemical proprieties. A proper selection of activated carbons allows reaching a capacitance of several hundred farads per gram in aqueous electrolytes. To exceed this value, a faradaic contribution to the charge storage can be added to the purely capacitive process by grafting redox molecules. It has been reported that with appropriate electroactive molecules, the total capacitance can be doubled in aqueous electrolytes. However, the grafting of molecules is often accompanied by a decrease of the intrinsic performance of the carbon, such as the double-layer capacitance and the ionic transportation within the porous structure. To circumvent these difficulties, we propose to use the organic binder as a platform for the grafting, to increase the overall capacity while minimizing the loading of inactive components in the electrode and preventing damage to the carbon. Practically, because carbon powder cannot be used alone to fabricate an electrode, the carbon powder is commonly mixed with an organic binder and a conductive additive, such as carbon black, to obtain a carbon paste with suitable mechanical and electrical properties. In such composite electrode, the binder does not contribute to the charge storage process and reduces the gravimetric capacitance. One approach for improving performance without decreasing the double-layer capacitance contribution and hindering the ionic transportation is to use the binder for the charge storage by grafting molecules onto its polymeric skeleton. In this way, the redox binder is expected to have the dual functionality of both the binder and the active material.Here, this original approach will be demonstrated with a modified binder prepared by reaction between in situ generated O-protected 3,4-dimethoxybenzenediazonium ions and polystyrene. The charge storage properties of the electrode using the modified binder will be compared to those of an electrode based on modified carbon powder to determine the potential usefulness of such redox active binder.

National audience; Activated carbons are attractive materials for supercapacitors due to their physical and chemical proprieties. They present a typical capacitance comprises between 100 and 150 F.g-1. One of the most popular strategies to improve their specific capacitance consists in adding a faradaic contribution by grafting redox molecules. However, both the double-layer capacitance of the carbon and the internal resistance suffer from the grafting. In this work, we propose to graft the organic binder with redox molecules instead of carbon, in order to concomitantly obtain a large capacitance value and an efficient ionic transportation within the porous structure of the carbon, which is promising for enhancing both energy and power densities.

International audience; Recent developments at IMN will be shared on several research directions out of usual paths for performance improvement of Li-ion batteries. We will focus on innovative surface modifications of electrode components, new electrode compositions and architectures, and failure mechanism upon cycling by in-depth characterization through coupled advanced spectroscopic techniques.A molecular grafting approach has been proposed as a way to modify the interfacial chemical reactivity of oxide materials, which is detrimental to their long-term energy storage properties as electrodes of Li-ion batteries. Surface derivatization of powder oxide materials such as Li1.2V3O8 and Li(Mn,Ni)2O4 was accomplished by in situ electrografting of a diazonium salt during Li-ion intercalation, leading to a covalently bonded organic multilayer. Charge transfer is not impeded, while electrolyte decomposition is inhibited thus increasing the cycle life and decreasing the self-discharge. Carbon additives of classical porous electrodes occupy a large volume fraction which is lost for charge storage. Redox functionalization of the surface of some carbon additives has been successfully achieved through non-covalent grafting chemistry using multi-redox pyrene molecules synthesized on purpose. Such functionalized carbon additives have been used to increase the stored energy and power of C-coated LFP porous electrodes.Thicker electrodes are needed for higher energy density Li-ion batteries. We evaluate different directions in order to design new innovative electrode architectures for such a purpose. Our grafting chemistry has been further developed to achieve molecular junctions between non-carbon-coated LFP and multiwall carbon nanotubes (MWCNT) using a designed thiophene-based conjugated molecule. The strategy enables original architecturing of the cathode of Li-ion batteries, with the individual MWCNT being electronically nanocontacted at the surface of LFP grains. This advancement leads to much higher specific capacity and better capacity retention for non calendared thick electrodes, for which the electronic wiring of the electroactive material grains is a critical issue. Another direction followed is the use of conducting polymer additives in porous electrodes, which are able to act as both conducting fillers and mechanical reinforcement materials. We have synthesized a new form of lithium doped PANI, the excellent properties of which in terms of specific capacity, stability on cycling and rate capability will be presented. The coating of bare LFP particles with thin layers of this new Li-doped PANI allows surpassing the performance of commercial carbon coated LFP thick electrodes. The role of this PANI additive into millimetric thick electrodes of NMC material will also be discussed.Future developments of higher energy density Si-based Li-ion batteries depend on the mastering of side reactions at the Si anode. We will compare the SEI composition and morphology at the Si surface upon cycling in half cell and full Li-ion cell configurations using a combination of 7Li, 19F MAS NMR, XPS, TOF-SIMS and STEM-EELS. The origin of the much faster aging of Si-based full cells versus half cells and future directions for improvement will be discussed