Initiation of Carbon Nanofiber Growth on Polycrystalline Nickel Foam under Low Ethylene Pressure

The initiation of carbon nanofiber (CNF) growth on polycrystalline Ni foam was investigated by using a combination of ex situ and in situ methods, which include SEM, XRD, and Raman spectroscopy. Experiments were performed at a low hydrocarbon partial pressure to slow down the initiation process. Very little to no CNFs were observed on reduced samples, which is caused by diffusion of C to the bulk of the Ni foam. This prevents the formation of Ni₃C as a precursor of Ni nanoparticles at a low hydrocarbon partial pressure from acting as active particles for CNF formation. CNF growth was significant on oxidized samples and the initiation was slowed down by using an extremely low ethylene pressure. Ni nanoparticles are able to catalyze CNF growth, provided these are isolated from the Ni bulk by unreduced NiO, which results from the incomplete reduction of the NiO layer.