EDLC electrodes from cellulose-based carbon aerogels : influence of the carbon surface chemistry
Résumé
This work investigates the influence of the carbon surface chemistry on the carbon's electrochemical performance if used as EDLC electrode material. Carbon aerogels were synthesized by crosslinking cellulose acetate through a non-toxic isocyanate and subsequent drying in supercritical CO2 and pyrolysis in inert atmosphere (1000°C, nitrogen atmosphere). Subsequently, the surface chemistry of the carbon aerogels was modified by oxidation (in H2O2) or by nitrogen introduction (impregnation with melamine and co-pyrolysis). Thus the carbon material's surface chemistry was modified depending on the modification method, while the morphology remained similar. All carbon samples were analyzed in terms of morphology (by nitrogen adsorption and mercury porosimetry), composition (elemental analysis), and surface chemistry (Boehm titration and pHPZC). For electrochemical analysis, carbon aerogels were tested in the form of EDLC electrodes in a symmetric test assembly in aqueous electrolyte (cyclic voltammetry and galvanostatic cycling). Results show that the carbon's capacitance can be increased by the introduction of heteroatoms. However, the type of functional groups present on the carbon surface seems to really determine capacitance as opposed to the mere presence of oxygen or nitrogen atoms.
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