Influence of the nature of the metal hydroxide in the porosity development of carbon nanofibers

In this study, highly porous carbon nanofibers (CNFs) were prepared by chemical activation in order to develop promising energy storage materials. The activation was performed at a temperature of 850 °C by using different metal hydroxides as the activating agents. Pore structures of the CNFs were analyzed using N2/77 K adsorption isotherms. The presence of oxygen groups was analyzed by means of acid–base titration. The structural order (crystallinity) of the materials was studied by XRD and TGA analysis and the morphology and diameter distributions by means of TEM. The use of hydroxide of alkaline metals of low melting and boiling points (K, Rb, and Cs) led to the best results of porosity development. On the contrary, the pore opening was lower if the alkaline metal had a high boiling point (Na) or when alkali earth cations were used as activating agents. After the activation, the porous CNFs showed a decrease in diameter and scratches on their surfaces, as a consequence of the surface oxidation and opening of the graphitic layers, respectively. It was found that the specific surface area of the porous CNFs prepared using KOH and RbOH was more than 400 and 280 m2 g−1, respectively, without loss of their fiber shape.

The proportions of ultramicropores, supermicropores, and mesopores of activated carbon nanofibers depend on the metal used for activation. The porosity development was higher when metals with low boiling points were used as activating agent.Figure optionsDownload as PowerPoint slide