Experimental and theoretical studies of tetramethoxy-p-benzoquinone: infrared spectra, structural and lithium insertion properties

International audienceIn the search for low-polluting electrode materials for batteries, the use of redox-active organic compounds represents a promising alternative to conventional metal-based systems. In this article we report a combined experimental and theoretical study of tetramethoxy-p-benzoquinone (TMQ). In carbonate-based electrolytes, electrochemical behaviour of this compound is characterized by a reversible insertion process located at approximately 2.85 V vs. Li+/Li0. This relatively high potential reactivity, coupled with our effort to develop computational methodologies in the field of organic electrode materials, prompted us to complement these experimental data with theoretical studies performed using density functional theory (DFT). Single crystals of TMQ were synthesized and thoroughly characterized showing that this quinonic species crystallised in the P21/n space group. The experimental crystal structure of TMQ was then used to assess various DFT methods. The structural features and vibrational spectra were thus predicted by using as a whole five common density functionals (PBE, LDA, revPBE, PBEsol, B3PW91) with and without a semi-empirical correction to account for the van der Waals interactions using either Grimme's (DFT-D2) or Tkatchenko-Scheffler (TS) scheme. The most reliable combination of the DFT functional and the explicit dispersion correction was chosen to study the Li-intercalated molecular crystal (LiTMQ) with the view of indentifying Li insertion sites. A very close agreement with the experiment was found for the average voltage by using the most stable relaxed hypothetical LiTMQ structure. Additionally, a comparison of vibrational spectra gained either for TMQ molecule and its dimer in gas phase or through periodic calculation was undertaken with respect to the experimentally measured infrared spectra. The topological features of the bonds were also investigated in conjunction with estimates of net atomic charges to gain insight into the effect of chemical bonding and intermolecular interaction on Li intercalation. Finally, π-electron delocalization of both quinone and alkali salts of p-semiquinone were determined using the Harmonic Oscillator model of Aromaticity (HOMA) or aromatic fluctuation index (FLU) calculations

Systèmes hybrides organique/ inorganique fonctionnels basés sur des formes moléculaires de chalcogénures de rhénium (III) à cluster octaédrique

The chemistry of octahedral rhenium chalcogenide molecular cluster is a field at the crossroads of organic/inorganic hybrid materials and solid state chemistry. These compounds are known for their electronic and photo-active properties. The first part of this work is concerned with the use of [Re6Se8(CN)6]4- as an octahedral nanonode in order to direct the extended structure of radical cation salts based on tetrathiafulvalene (TTF) derivatives, also exploiting the ability of cyanide groups to direct crystal structures through directional CN-...I halogen bonds. The efficiency of these weak bonds is evidenced in a ternary radical cation salt where a neutral dihalogenated organic molecule acts as a spacer between two clusters. The anionic structural organization of the salt affects the electronic properties of the material. Further to this result, synthesis of other dihalogenated spacers has been carried out followed by electrocristallization experiments. The second part of this work is, in the one hand, dedicated to the exploration of the molecular form [Re6Se8(CH3CN)6](SbF6)2 reactivity towards acetylenide. This approach takes part to the current debate concerning the nature of the electronic structure of these clusters. In another hand, we consider the well known reactivity of pyridine derivatives towards the former cluster to investigate new functional ligands based on this moiety. Ligand functionalization confers novel interesting properties to the cluster, depending on the nature of the terminal group.La chimie des formes moléculaires électro et photo-actives de chalcogénures à clusters octaédriques de Re(III) est un domaine frontière au carrefour des matériaux hybrides organiques/inorganiques et de la chimie du solide. La première partie de ce travail de thèse concerne l'utilisation du cluster [Re6Se8(CN)6]4- comme noeud octaédrique pour orienter l'organisation de la structure étendue de sels de radicaux cations de dérivés du tétrathiafulvalène (TTF). Les groupements cyano sont connus en ingénierie cristalline pour leur aptitude à diriger les structures cristallines par le biais de liaisons halogène directionnelles CN-...I. Ces liaisons faibles ont été mises en oeuvre dans un sel de radical cation ternaire, où une molécule organique neutre di-halogénée joue le rôle d'espaceur entre deux clusters. L'organisation de la structure anionique du sel peut modifier les propriétés électroniques du matériau. Ce résultat a conduit à synthétiser d'autres espaceurs polyhalogénés et à les engager dans des expériences d'électrocristallisation. La seconde partie de ce travail est, pour une part, consacrée à l'exploration de la réactivité des formes moléculaires [Re6Se8(CH3CN)6](SbF6)2 vis-à-vis de ligands acétylénures. Cette approche est motivée par le débat actuel sur la nature de la structure électronique de ces formes moléculaires. D'autre part, la réactivité établie de ce cluster avec des dérivés de la pyridine nous a conduits à développer de nouveaux ligands fonctionnels basés sur ce motif. La fonctionnalisation des ligands confère au cluster de nouvelles propriétés qui dépendent de la nature du groupement terminal

Voltage Gain in Lithiated Enolate-Based Organic Cathode Materials by Isomeric Effect

International audienceLi-ion batteries (LIBs) appear nowadays as flagship technology able to power an increasing range of applications starting from small portable electronic devices to advanced electric vehicles. Over the past two decades, the discoveries of new metal-based host structures, together with substantial technical developments, have considerably improved their electrochemical performance, particularly in terms of energy density. To further promote electrochemical storage systems while limiting the demand on metal-based raw materials, a possible parallel research to inorganic-based batteries consists in developing efficient and low-polluting organic electrode materials. For a long time, this class of redoxactive materials has been disregarded mainly due to stability issues but, in recent years, progress has been made demonstrating that organics undeniably exhibit considerable assets. On the basis of our ongoing research aiming at elaborating lithiated organic cathode materials, we report herein on a chemical approach that takes advantage of the positive potential shift when switching from para to ortho-position in the dihydroxyterephthaloyl system. In practice, dilithium (2,3-dilithium-oxy)-terephthalate compound (Li4C8H2O6) was first produced through an eco-friendly synthesis scheme based on CO2 sequestration, then characterized, and finally tested electrochemically as lithiated cathode material vs. Li. This new organic salt shows promising electrochemical performance, notably fast kinetics, good cycling stability and above all an average operating potential of 2.85 V vs. Li+/Li (i.e., +300 mV in comparison with its para-regioisomer), verifying the relevance of the followed strategy

A rechargeable lithium/quinone battery using a commercial polymer electrolyte

The present study reports superior electrochemical performance with capacity doubled for organic positive electrodes based on a small redox-active molecule when using the Lithium Metal Polymer (LMP) technology. Particularly, the simple use of the regular solid polymer electrolyte currently employed in commercial LMP cells allows obtaining for the first time an efficient two-electron cycling of tetramethoxy-p-benzoquinone with high-rate capability at temperatures as high as 100 °C. With no optimization, the restored capacity represents 80% of the theoretical value (190 mAh/g) after 20 cycles operated at a C rate. On the contrary, when cycled in conventional carbonate-based electrolytes, this quinone compound exhibits quite poor electrochemical features such as a very limited depth of discharge (~50% of the theoretical capacity in the first cycle) followed by rapid capacity decay. After cycling, preliminary post-mortem characterizations did not evidence any obvious degradation in the cell. Although the adverse effect of the diffusion of the active material is not fully inhibited, the coulombic efficiency is close to 100% while the Li/electrolyte interface appears stable. Keywords: Organic electroactive material, Organic battery, Solid polymer electrolyte, Li-battery, Tetramethoxy-p-benzoquinon

Pyrolysis reaction of squaric acid: A one-step method for producing expanded foam of mesoporous carbon

International audienceA template-free approach is described for the synthesis of expanded foams of mesoporous carbon exhibiting high surface areas ranging from 550 to 1100 m2/g. The procedure is based on the exceptional carbonization reaction that occurs with squaric acid (H2C4O4), a strained four-membered carbocycle belonging to the oxocarbon acids. Indeed the pyrolysis reaction proceeds just above 300°C through an amazing one-step and sharp exothermic phenomenon coupled with a weight loss of 90%, thereby promoting a porous structure. This massive gas release behaves also as a "fluid" template during the carbon production, which explains the formation of expanded foams. This particular thermal behaviour seems related to the phase transition that occurs in H2C4O4 crystals at Tc=121°C. Below Tc the planar squaric acid molecules exhibit a fully ordered structure in a monoclinic system whereas for T>Tc the structure undergoes a disordered tetragonal structure where all C-O bonds of squaric acid become statistically equivalent in a perfect square, making a discrete thermal decomposition reaction possible

The low/room-temperature forms of the lithiated salt of 3,6-dihydroxy-2,5-dimethoxy-p-benzoquinone: a combined experimental and dispersion-corrected density functional study

International audienceFollowing our first experimental and computational study of the room temperature (RT) form of the tetrahydrated 3,6-dihydroxy-2,5-dimethoxy-p-benzoquinone dilithium salt (Li2DHDMQ?4H2O), we have researched the occurrence of hydrogen ordering in a new polymorph at lower temperature. The study of polymorphism for the Li2DHDMQ?4H2O phase employs both experimental (single crystal X-ray diffraction) and theoretical approaches. While clues for disorder over one bridging water molecule were observed at RT (b form), a fully ordered model within a supercell has been evidenced at 100 K (a form) and is discussed in conjunction with the features characterizing the first polymorphic form reported previously. Density functional theory (DFT) calculations augmented with an empirical dispersion correction (DFT-D) were applied for the prediction of the structural and chemical bonding properties of the a and b polymorphs of Li2DHDMQ?4H2O. The relative stability of the two polymorphic systems is evidenced. An insight into the interplay of hydrogen bonding, electrostatic and van der Waals (vdW) interactions in affecting the properties of the two polymorphs is gained. This study also shows how information from DFT-D calculations can be used to augment the information from the experimental crystal diffraction data and can so play an active role in crystal structure determination, especially by increasing the reliability and accuracy of H-positioning. These more accurate hydrogen coordinates allowed for a quantification of H-bonding strength through a topological analysis of the electron density (atoms-in-molecules theory)

A green Li-organic battery working as a fuel cell in case of emergency

International audienceThe routine access to electricity always means a drastic change in terms of quality of life making it easierand safer. Consequently, the global electric demand both on and off-the-grid is growing and calls for ongoing innovation to promote reliable, clean and safe power supplies. In this context, the development of new chemistries for batteries and fuel cells could play a critical role. From our prospects aiming at fostering the concept of sustainable organic batteries, we report in this article on the peculiar properties of dilithium (2,5-dilithium-oxy)-terephthalate salt, a novel redox-active material. Based on an oriented retrosynthetic analysis, we have succeeded in elaborating this organic electrode material through an original and low-polluting synthesis scheme, which includes both chemical and biochemical CO2 sequestration in conjunction with a closed-loop solution for recycling products. Beyond its remarkable electrochemical performance vs. Li, especially as a lithiated cathode material, this compound behaves also like an oxygen scavenger. This dual electrochemical/chemical reactivity makes the self-recharging of a Li cell based on this organic salt possible by opening it to air ensuring an electrical power reserve when a conventional electrical recharge is not possible. In such a case, the pristine rechargeable Li-organic battery operates as a sort of "Li/O2 fuel cell"

High-Potential Reversible Li Deintercalation in a Substituted Tetrahydroxy-p-benzoquinone Dilithium Salt: An Experimental and Theoretical Study

International audiencePromoting the emergence of efficient organic Li-ion batteries requires notably air-stable lithiated organic structures able to reversibly deintercalate Li at high enough potential values. To date, most of cathode materials reported in the literature are typically synthesized in their fully oxidized form, which restricts the operating potential of such materials and supposes the use of an anode material in its lithiated state. Reduced forms of quinonic structures could represent examples of lithiated organic-based cathode able to deintercalate Li+ at potentials higher than 3 V thanks to substituent effects. Having previously recognized the unique electrochemical properties of the C6O6-type ring, we have designed then elaborated through a simple three-step method the lithiated salt of 3,6-dihydroxy-2,5-dimethoxy-p-benzoquinone, a new redox amphoteric system deriving from the tetralithium salt of tetrahydroxy-p-benzoquinone. Electrochemical investigations have particularly revealed that such an air-stable salt may reversibly deintercalate one Li+ upon charging with a practical capacity of about 100 mAh g1 at near 3 V with, however, a polarization effect. Better capacity retention was successfully obtained by simply adding an adsorbing additive. A tetrahydrated form of the studied salt was also characterized from XRD and first-principles calculations. Various levels of theory were probed including DFT with classical functionals (LDA, GGA, PBEsol, revPBE) and models for dispersion corrections to DFT. One of the modified dispersion-corrected DFT schemes, related to a rescaling of both van der Waals radii and s6 parameter, provides significant improvements for the description of this crystal kind over other treatments. We then applied this optimized approach to the screening of hypothetical frameworks for the delithiated phases and to the search for the anhydrous structure

Electrochemical properties of crystallized dilithium squarate: insight from dispersion-corrected density functional theory.

International audienceThe stacking parameters, lattice constants, and bond lengths of solvent-free dilithium squarate (Li(2)C(4)O(4)) crystals were investigated using density functional theory with and without dispersion corrections. The shortcoming of the GGA (PBE) calculation with respect to the dispersive forces appears in the form of an overestimation of the unit cell volume up to 5.8%. The original Grimme method for dispersion corrections has been tested together with modified versions of this scheme by changing the damping function. One of the modified dispersion-corrected DFT schemes, related to a rescaling of van der Waals radii, provides significant improvements for the description of intermolecular interactions in Li(2)C(4)O(4) crystals: the predicted unit cell volume lies then within 0.9% from experimental data. We applied this optimised approach to the screening of hypothetical framework structures for the delithiated (LiC(4)O(4)) and lithiated (Li(3)C(4)O(4)) phases, i.e. oxidized and reduced squarate forms. Their relative energies have been analysed in terms of dispersion and electrostatic contributions. The most stable phases among the hypothetical models for a given lithiation rate were selected in order to calculate the corresponding average voltages (either upon lithiation or delithiation of Li(2)C(4)O(4)). A first step towards energy partitioning in view of interpretating crystal phases relative stability in link with (de)-intercalation processes has been performed through the explicit evaluation of electrostatic components of lattice energy from atomic charges gained with the Atoms in Molecules (AIM) method

Monitoring systems for resistance to plant protection products across the world: Between redundancy and complementarity

International audienceBACKGROUND Monitoring resistance to plant protection products (PPPs) is crucial for understanding the evolution of resistances in bioagressors, thereby allowing scientists to design sound bioagressor management strategies. Globally, resistance monitoring is implemented by a wide range of actors that fall into three distinct categories: academic, governmental, and private. The purpose of this study was to investigate worldwide diversity in PPP resistance monitoring systems and to shed light on their different facets.RESULTS A large survey involving 162 experts from 48 countries made it possible to identify and analyze 250 resistance monitoring systems. Through an in-depth analysis, the features of the different monitoring systems were identified. The main factor differentiating monitoring systems was essentially the capabilities (funding, manpower, technology, etc.) of the actors involved in each system. In most countries, and especially in those with a high Human Development Index, academic, governmental, and private monitoring systems coexist. Overall, systems focus far more on monitoring established resistances than on the detection of emerging resistances. Governmental and private resistance monitoring systems generally have considerable capacities to generate data, whereas academic resistance monitoring systems are more specialized. Governmental actors federate and enroll a wider variety of stakeholders.CONCLUSION The results show functional complementarities between the coexisting actors in countries where they coexist. We suggest PPP resistance monitoring might be enhanced if the different actors focus more on detecting emerging resistances (and associated benefits) and increase collaborative and collective efforts and transparency