Pseudoeffects from Heteroatoms in the Carbon Network

The beneficial effect of nitrogen in the composite with an incorporated nanotubular backbone has been clearly demonstrated. Melamine was the carbon precursor rich in nitrogen (45 wt%) hence, polymerized blends of melamine with formaldehyde allow various nitrogenated composites to be prepared. The carbon composites have been obtained by polymerization of melamine with formaldehyde (without any catalyst) in the presence of a controlled amount of multiwalled carbon nanotubes. Such a polymerized blend was carbonised at 750°C for 1 h under nitrogen flow. The final carbonization product was named M-l-F (i.e., melamine and formaldehyde without carbon nanotubes), whereas Nt- -M-l-F means composite with carbon nanotubes 2M and 3M stand for a twofold and threefold melamine proportion in the blend, respectively. The results of elemental analysis showed that the nitrogen content varied in the final product from 7.4 to 21.7 wt% (Table 9.1). The oxygen content was calculated by difference and its amount was comparable in all the samples varying from 5.9 to 7.8 wt%. The 

It is important to stress that the values from elemental analysis and from XPS are very comparable, which is a proof of the same perfect distribution of nitrogen in the bulk of the carbon network 

The nitrogen adsorption/desorption isotherms allow the specific surface area, pore size distribution as well as the micro/meso ratio to be estimated. The total surface area is quite similar for the investigated samples and it ranges from 329 to 403 m /g being the most developed for the Nt+3M+F composite as shown in Fig. 9.6. The nitrogen adsorption isotherms showed that the carbon materials are typically mesoporous (apart from the material M+F, that is, without nanotubes), and the amount of micropores is very moderate. The micropore volume values for all the samples are comparable var3dng from 0.152 to 0.174 cm /g. The porosity characteristics of all the composites are illustrated in Table 9.1. 

The electrochemical performance of the nitrogen-enriched composites used as electrodes in supercapacitors is determined by the 

Trials were undertaken to explain the electrochemical behavior of both electrodes separately. For that, a two-electrode capacitor was charged/discharged at 1 A/g current load by controlling simultaneously the potential for both electrodes. Such characteristics for the Nt+2M+F composite operating in acidic medium are shown in Fig. 9.8. It is interesting to note that the capacitance of the total capacitor is equal to 148 F/g, whereas the positive electrode shows 133 F/g and the negative one 166 F/g. (All values are expressed per electrode). It shows that both electrodes have a different contribution to the total capacitance. 

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