PORE STRUCTURE AND CAPACITOR PERFORMANCE OF N-ENRICHED CARBON FOAM

摘要

Nitrogen-enriched carbons are now regarded as a noteworthy candidate for supercapacitor electrode. Substitutionally placed nitrogen atom in carbon framework can display notable additional capacitance (～200F/g) based on the faradaic mechanisms especially in acid medium. Moreover, an exceptionally high cyclic durability can be realized despite the pseudo capacitive regime. The origin of such a high capacitance of N-enriched carbon seems to be due to the interaction between proton and nitrogen atom. However, this explanation is not wholly convincing. Actually, this sort of carbon also develops rather high capacitance in alkaline electrolytes. The capacitance is not so high as in acids, but beyond expectation.Another remarkable feature of N-enriched carbon electrode is less indispensability for pore structure. The capacitance obtained using N-enriched carbons is often very far from the value expected by its BET specific surface area estimated by nitrogen adsorption at 77K (BET-SSA-N_2) which is practically standardized method for evaluation of porous electrode materials. Even if taking into account the electrochemical interactions, the obtained capacitance per unit surface area is abnormally enormous. This fact compels us to find persuasive argument. Accordingly, in the present system, we should notice that BET-SSA-N_2 is not always comparable for the effective surface area of porous electrodes. For several years, we have been interested in electrochemical performance of a series of nitrogen-enriched carbons prepared from nitrogen containing organic precursors by carbonization . Recently, we have reported N-enriched carbon foams can be realized by the carbonization of melamine foams, which are mass-produced as washing sponge . The obtained carbon foams appeared representative electrochemical properties of this sort, for instance, almost rectangular shape of cyclic voltammograms and high capacitance going up to over 250F/g. In this way, the carbon foam can be considered as a suitable electrode material for discussing the electrochemistry of N-enriched carbon into details; besides good productivity and convenient handling are advantageous factor from an experimental aspect. The present study describes electrochemical properties of N-enriched carbon foam mainly from the viewpoint of the surface characteristics of electrode.