On the importance of the structure in the electrical conductivity of fishbone carbon nanofibers

Carbon nanofibers (CNFs) have a remarkable electrical conductivity resulting highly attractive for different applications such as composites or electronics due to their high quality/price ratio. Although it is known that their graphitic character provides a high conductivity, very little is known about the influence of the nanofibers structure on that property. In this study, CNFs characterized by different physical properties are prepared at diverse synthesis temperatures within a range (550ºC-750ºC) in which significant structural and dimensional changes are accomplished and homogeneous nanofiber growth takes place. The electrical conductivity is determined on the powdery as-grown materials modifying the compaction degree by applying pressure. Because of a combination of structural features, the apparent electrical conductivity increases with synthesis temperature of CNFs, ranging from 50 S m-1 for the worst conducting CNFs at a low compaction degree (25% of solid volume fraction), to 3·103 S m-1 for the best conducting CNFs at a high compaction degree (60% of solid volume fraction). Further analysis is carried out applying the percolation theory to analyze the experimental data and the results suggest that both the orientation of the graphenes and the filament diameter distribution play a determining role in the intrinsic electrical conductivity, with values in the interval 1.5·103 to 1.3·104 S m-1. These intrinsic values of electrical conductivity are found between one and two orders of magnitude higher than that of the powder, highlighting the also important effect of porosity.