About the octopus-like growth mechanism of carbon nanofibers over graphite supported nickel catalyst

Carbon nanofibers (CNFs) with a uniform diameter of ca. 30 nm and a productivity of 50 g/(gNih) were grown by catalytic decomposition of a C2H6/H2 mixture over a nickel (1 wt%) catalyst supported on graphite microfibers, which constitutes the macroscopic shape of the final C/C composite. The catalyst particle size and dispersion before CNF growth was characterized by high-resolution scanning electron microscopy (SEM). The resulting composite consisting of a weblike network of CNFs covering the starting catalyst was characterized by SEM and transmission electron microscopy to gain more insight into the relationship between the starting nickel catalyst particles and the as-grown CNFs. Apparently, CNF growth proceeds from different mechanisms: a base-growth mechanism, involving especially the large nickel particles; a tip-growth mechanism, involving mostly the smaller nickel particles; and a tip/octopus-growth mechanism (the most common), involving all particles. In all cases, restructuring of the nickel particle from a globular to a more faceted structure seems to be the key step in producing an extremely large quantity of CNFs with yields up to 100 wt%.