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Use of an electroactive organic binder as active material for high energy density supercapacitors
C Benoit, D. Belanger, C. Cougnon
To cite this version:
C Benoit, D. Belanger, C. Cougnon. Use of an electroactive organic binder as active material for high energy density supercapacitors. Congrès de la SCF “ Chimie et transition énergétique ”, Jul 2015, Lille, France. �hal-02547234�
Congrès de la Société Chimique de France – 2015 SCF Congress - 2015
Use of an electroactive organic binder as active material for high energy density supercapacitors.
Liant organique modifié pour supercondensateurs à haute densité d’énergie.
C. Benoit1, D. Bélanger2, C. Cougnon1*
1 Laboratoire MOLTECH Anjou, UMR-CNRS 6200, Université d’Angers, 2 Boulevard Lavoisier 49045, Angers Cedex, France
2 Département de Chimie, Université du Québec à Montréal, case postale 8888, succursale centre-ville, Montréal, Québec H3C 3P8, Canada
* Corresponding author: [email protected]
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Résumé :
Grace à leurs propriétés physiques et chimiques uniques, les carbones activés sont un matériau de choix pour la fabrication de supercondensateurs. Ils présentent typiquement des capacités de 100 à 150F/g. Une des stratégies les plus utilisées pour améliorer cette capacité de stockage consiste à greffer des molécules redox sur le substrat carboné. Malheureusement le greffage altère la capacité de double couche du carbone. Nous proposons d’étudier un liant organique modifié avec des unités redox pour améliorer les performances des dispositifs et empêcher la perte de la capacité de double couche.
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Summary:
Activated carbons are attractive materials for supercapacitors due to their physical and chemical proprieties. They present a typical capacitance comprises between 100 and 150F.g-1. One of the most popular strategies to improve the capacitance consists in adding 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 binder with redox molecules instead of carbon, in order to prevent decrease of the double layer capacitance of carbon and improve the performances of devices.
Keywords: Supercapacitors; activated carbon; organic binder; grafting
Les supercondensateurs sont de nos jours utilisés dans de nombreux domaines, comme l’aviation (ouverture d’urgence), l’automobile (récupération d’énergie au freinage) ou encore pour le stockage d’énergie électrique. Ils présentent la capacité à stocker en quelques secondes une quantité importante de charges grâce à leur résistance interne très faible.
Malheureusement leur capacité de stockage encore trop faible limite leur utilisation à grande échelle, et c’est dans ce cadre que s’inscrivent nos recherches
1 Introduction
Activated carbons are attractive material for supercapacitors due to the extremely low separation of ions and electron charges associated with a large specific surface area. However, because it can’t be easily handled as electrodes component, carbon powder are generally mixed to an organic binder and conductive additive to obtain a carbon paste with suitable mechanical and electrical proprieties.
To increase the specific capacitance value of the activated carbon, a popular strategy is to graft redox molecules to add a faradaic contribution to the capacitive one of the carbon. [1,2] In this approach, the binder is considered as a dead- weight for the charge storage. In this work, we propose to use the binder as a charge storage component, by grafting electroactive molecules onto its polymeric skeleton. Such redox binder is expected to have the dual functionality of both binder and active material.
2 Experimental/methodology
Polystyrene used as binder was modified by reaction in THF with O-protected 3,4- dimethoxyaniline in situ diazotized. After 108h stirring at room temperature, the solvent was removed under vacuum. The residue was purified by chromatography on silica gel (eluents CH2CL2/MEOH 99/1, CH2CL2/MEOH 95/5 and pure MEOH) affording a brown powder.
Electrodes were prepared by mixing carbon powder (YP80F, KURAKAY) with modified or raw binder (10 w% in N-methyl pyrrolidinone) and carbon black (superior graphite) with a ratio of 80:10:10. The mixture was stirred for one day until a homogenous ink was obtained. As counter electrodes, unmodified carbon and polystyrene were used and 0,2ml of carbon ink was deposited onto the gold disk. As working electrodes modified and unmodified carbon was mixed with modified or unmodified polystyrene and 0,1ml of the carbon ink was deposited onto a platinum disk. After drying at 120°C for 3 hours, thin films of 1-3 mg were obtained.
Electrochemical measures were performed at room temperature in an aqueous sulfuric acid (1M) electrolyte with a three-electrode test cell ECC-
AQU (EL-ELL, Germany). Potential are referred to Ag/AgCl reference electrode. A potentiostat- galvanostat model VSP (Bio-Logic) monitored by EC-lab software was used.
3 Results and discussion
Here, we propose to reconsider the binder for the charge storage by grafting molecules onto its polymeric skeleton. This original approach was tested with a modified binder prepared by reaction between O-protected 3,4-dimethoxyaniline in situ diazotized and polystyrene. The resultant carbon electrode was compared to an electrode based on modified carbon powder to study the performances according to the way molecules were attached (i.e., onto the organic binder or carbon powder). The scheme in Figure 1 resumes the different combinations of the two modified components used as active materials in this work.
Figure 1 shows typical cyclic voltammograms (CVs) recorded in 1 M H2SO4 on working electrodes prepared from modified binder or modified carbon powder, compared to the response of an unmodified electrode. Note that, just before use, carbon electrodes were first cyclized between 0 V and 1.1 V vs. Ag/AgCl in 1 M H2SO4 to remove the two methyl protecting groups by electrochemical oxidation and restore the well-known redox activity of the catechol. At relative low scan rate, the CV recorded on the unmodified electrode shows a quasi-rectangular shape, which is characteristic of a nearly pure capacitive behavior. With the electrode based on modified carbon, the CV is characterized by an intense reversible electrochemical system centered at around 0.1 V, accompanied to a retarded current when the potential sweep is reversed. When the working electrode contains the modified binder, the CV reveals a similar redox system, whilst the current intensity is highly increased over the entire potential domain scanned.
The global specific capacitance values determined by integrating the area under the CVs are 110 Fg-1 for the unmodified electrode, 180 Fg-1 for the modified-carbon-based electrode and 240 Fg-1 for the modified-binder-based electrode.
As it was expected, when redox molecules are introduced, an additional faradaic capacitance is obtained over a narrow potential window where the redox reaction occurs. However, it is noteworthy that the best result is obtained with the modified- binder-based electrode, which contain only 10 weight % of redox binder, compared to the carbon powder, which is the main component (80 weight
%). This unprecedented result can be explained by the fact that the grafting onto the binder does not damage the double-layer capacitance of the carbon, and by an improved wettability of the composite network that increases the pores accessibility and favors the ions adsorption processes.
-4 -3 -2 -1 0 1 2 3 4
-0.4 -0.2 0 0.2 0.4 0.6
Current (Ag-1)
Potential (V)
unmodified electrode modified carbon modified binder
Fig. 1. Cyclic voltammograms recorded in 1M H2SO4 at 10mV.s-1 on unmodified electrode, modified-carbon-based electrode and modified-binder-based electrode.
4 Conclusions
This work points the interest of using an electroactive organic binder as active material. By this strategy, the total capacitance can be doubled, the equivalent series resistance decreased, while a good stability was obtained.
Acknowledgements
This work is supported by the Centre National de la Recherche Scientifique (CNRS-France) and the Agence National de la Recherche (ANR) through the project ICROSS
References
1. Pognon, G., et al., Catechol-Modified Activated Carbon Prepared by the Diazonium Chemistry for Application as Active Electrode Material in Electrochemical Capacitor. ACS Applied Materials &
Interfaces, 2012. 4(8): p. 3788-3796.
2. Pognon, G., et al., Performance and stability of electrochemical capacitor based on anthraquinone modified activated carbon. Journal of Power Sources, 2011. 196(8): p. 4117-4122.
