Nouvelles stratégies de production in situ de sels de diazonium pour la modification éléctrochimique de surfaces

Date du colloque : 07/2011</p

Conception et caractérisation d’une batterie organique obtenue par greffage direct de molécules électroactives sur carbone activé

Date du colloque : 07/2013</p

Toward fully organic rechargeable charge storage devices based on carbon electrodes grafted with redox molecules

Activated carbon powders modified with naphthalimide and 2,2,6,6-tetramethylpiperidine-N-oxyl were assembled into a hybrid electrochemical capacitor containing an organic electrolyte. The fully organic rechargeable system demonstrated an increase in specific capacitance up to 51%, an extended operating voltage of 2.9 V in propylene carbonate, compared to 1.9 V for the unmodified system, and a power 2.5 times higher

Effect of the porous texture of activated carbons on the electrochemical properties of molecule-grafted carbon products in organic media

Two commercial activated carbons, different from their texture, were grafted with electroactive molecules and tested for determining what texture is well-suited for the grafting. Microporous and mesoporous carbons, having approximately the same BET surface area, were selected. The electroactive molecule consists in a naphthalimide compound having an amine as surface attachment group. The present work was divided in two parts. In a first part, the modified carbons were characterized by thermal gravimetric analysis, X-ray photoelectron spectroscopy, elemental chemical analysis and nitrogen gas adsorption measurements have been used for studying the impact of the grafting on the textural properties of carbons. In a second part, the electrochemical properties of the modified carbons were studied in propylene carbonate +1 M Bu4NBF4. Results show that the grafting ruins the performances of the microporous carbon, while the mesoporous carbon appears well-suited for the grafting, showing a good compromise between electrolyte-accessibility and ionic transportation

Direct introduction of redox centers at activated carbon substrate based on acid-substituent-assisted diazotization

Redox properties have been imparted to activated carbon with a high degree of functionalization by chemical grafting of 2-amino-4,5-dimethoxybenzoic add in situ diazotized. The diazotization reaction was accomplished in the presence or in the absence of HCl for estimating the positive or negative effect of the carboxylic acid substituent on the grafting yield. Thermal gravimetric analysis, X-ray photoelectron spectroscopy and cyclic voltammetry experiments show that when the carboxylic acid group participates to the diazotization reaction. the grafting yield is improved and becomes even better than when the carboxylic group is not present, increasing the capacitance of pristine carbon electrode from 120 to 200 F/g

Study of the air-formed oxide layer at the copper surface and its impact on the copper corrosion in an aggressive chloride medium

The electrochemical behaviour of pre-oxidized copper surfaces prepared by heating in air at 90°C was studied to evaluate the impact of the air-formed oxide layer at the copper surface on the corrosion in an aggressive chloride medium. In a first part, the evolution of the chemical composition and the structure of the air-formed oxide layer with the heating time were investigated by cyclic voltammetry in an alkaline medium in which the different oxide species can be discriminated, X-ray photoelectrons spectroscopy experiments (XPS) and water contact angle measurements. It was demonstrated that short heating times produce Cu2O-rich films, while CuO-rich films were obtained after long heating-time periods. Furthermore, cyclic voltammetric data strongly support a stratification of the corrosion products in the mature oxide layer. In a second part, the protection efficiency of air-formed films, aged from 1 to 22 days, against the copper corrosion was study using a potentiodynamic technique and the electrochemical impedance spectroscopy (EIS) in an aerated 0.2 M NaCl aqueous electrolyte. Results demonstrate that the chemical composition of the air-formed oxide layer has an important impact in the overall corrosion process. Results are tentatively explained in terms of composition and structure of the oxide layer

Impedance spectroscopy study of a catechol-modified activated carbon electrode as active material in electrochemical capacitor

Modified activated carbon (Norit S-50) electrodes with electrochemical double layer (EDL) capacitance and redox capacitance contributions to the electric charge storage were tested in 1 M H2SO4 to quantify the benefit and the limitation of the surface redox reactions on the electrochemical performances of the resulting pseudo-capacitive materials. The electrochemical performances of an electrochemically anodized carbon electrode and a catechol-modified carbon electrode, which make use both EDL capacitance of the porous structure of the carbon and redox capacitance, were compared to the performances obtained for the pristine carbon. Nitrogen gas adsorption measurements have been used for studying the impact of the grafting on the BET surface area, pore size distribution, pore volume and average pore diameter. The electrochemical behavior of carbon materials was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The EIS data were discussed by using a complex capacitance model that allows defining the characteristic time constant, the global capacitance and the frequency at which the maximum charge stored is reached. The EIS measurements were achieved at different dc potential values where a redox activity occurs and the evolution of the capacitance and the capacitive relaxation time with the electrode potential are presented. Realistic galvanostatic charge/discharge measurements performed at different current rates corroborate the results obtained by impedance

Modeling interannual dense shelf water export in the region of the Mertz Glacier Tongue (1992-2007)

1] Ocean observations around the Australian-Antarctic basin show the importance of coastal latent heat polynyas near the Mertz Glacier Tongue (MGT) to the formation of Dense Shelf Water (DSW) and associated Antarctic Bottom Water (AABW). Here, we use a regional ocean/ice shelf model to investigate the interannual variability of the export of DSW from the Adélie (west of the MGT) and the Mertz (east of the MGT) depressions from 1992 to 2007. The variability in the model is driven by changes in observed surface heat and salt fluxes. The model simulates an annual mean export of DSW through the Adélie sill of about 0.07 ± 0.06 Sv. From 1992 to 1998, the export of DSW through the Adélie (Mertz) sills peaked at 0.14 Sv (0.29 Sv) during July to November. During periods of mean to strong polynya activity (defined by the surface ocean heat loss), DSW formed in the Adélie depression can spread into the Mertz depression via the cavity under the MGT. An additional simulation, where ocean/ice shelf thermodynamics have been disabled, highlights the fact that models without ocean/ice shelf interaction processes will significantly overestimate rates of DSW export. The melt rates of the MGT are 1.2 ± 0.4 m yr−1 during periods of average to strong polynya activity and can increase to 3.8 ± 1.5 m/yr during periods of sustained weak polynya activity, due to the increased presence of relatively warmer water interacting with the base of the ice shelf. The increased melting of the MGT during a weak polynya state can cause further freshening of the DSW and ultimately limits the production of AABW

Etude d’un dispositif hybride rechargeable entièrement organique pour le stockage électrochimique de l’électricité

Le développement de nouveaux dispositifs de stockage de l’électricité est un élément essentiel pour corriger l’intermittence des énergies éolienne et photovoltaïque, et garantir ainsi une bonne maîtrise des flux. Une stratégie prometteuse consiste à introduire des molécules organiques électroactives à la surface de carbones activés pour ajouter une contribution faradique au stockage de la charge électrique.[1] Cependant, les exemples de dispositifs hybrides tout organique sont encore très rares et la plupart des molécules sélectionnées sont électroactives en milieux aqueux.[2] Dans ce travail, nous avons sélectionné deux molécules électroactives en milieux organiques qui se complètent idéalement pour la préparation d’un dispositif de stockage hybride entièrement organique (Figure 1). Chaque électrode est conçue pour fonctionner sur un domaine de potentiel optimal afin de maximiser la densité d’énergie. Les performances de ce dispositif ont été évaluées dans une cellule Swagelok® à trois électrodes et comparées à celles d’un dispositif symétrique carbone-carbone constitué de poudre de carbone non-modifiée.[3] References [1] Pognon, G., Brousse, T., Demarconnay, L., Belanger, D. J. Power Sources 2011, 196, 4117. [2] Algharaibeh, Z.; Pickup, P.G. Electrochem. Commun. 2011, 13, 147. [3] Lebègue, E.; Brousse, T.; Gaubicher, J.; Retoux, R.; Cougnon, C. J. Mater. Chem. A 2009, 2, 8599

Spontaneous chemical modification of activated carbon powders by reduction of diazonium salts in situ generated by self-diazotization for energy storage applications

Date du colloque : 06/2011</p