Direct Synthesis of Nanofibrous Nonwoven Carbon Components: Initial Observations, Capabilities, and Challenges

Abstract

Widespread adoption of carbon nanomaterials has been hindered by inefficient production and utilization. A recently developed method has shown possibility to directly synthesize bulk nanostructured nonwoven materials from catalytically deposited carbon nanofibers (CNFs). The basic manufacturing scheme involves constraining carbon nanofiber growth to create three-dimensionally featured, macroscale products. Although previously demonstrated as a proof of concept, the possibilities and pitfalls of the method at a larger scale have not yet been explored. In this work, the basic foundation for using the constrained formation of fibrous nanostructures (CoFFiN) process is established by testing feasibility in larger volumes (as much as 2000% greater than initial experiments) and by noting the macroscale carbon growth characteristics. It has been found that a variety of factors contribute to determining the basic qualities of the macroscale fiber collection (nonwoven material), and there are tunable parameters at the catalytic and constraint levels. The results of this work have established that monolithic structures of nonwoven carbon nanofibers can be created with centimeter dimensions in a variety of cross-sectional shapes. The only limit to scale noted is the tendency for nanofibers to entangle with one another during growth and self-restrict outward expansion to the mold walls. This may be addressed by pregrowing carbon before placement or selective placement of the catalyst in the mold.

Parametric Effects of Mechanical Alloying on Carbon Nanofiber Catalyst Production in the Ni-Cu System

“…This could be increased significantly through proper scaling. Even at the present rate, the catalyst produced each minute is capable of depositing 200 g (or more) of carbon nanofibers in routine work [24]. Other methods of preparing this particular alloy may be even faster, but the ability to tailor the microstructure in other systems is a distinct advantage of MA, and this work provides general guidance and considerations that may be applied to many catalytic systems.…”

“…BET surface areas of the nanofibers were measured to be 66 m 2 /g (Ni 20 min), 32 m 2 /g (Ni 180 min), 221 m 2 /g (Ni 30% Cu 20 min) and 222 m 2 /g (Ni 30% Cu 180 min). All fibers were previously found to be highly amorphous [24], with little evidence of graphitic structure. …”

“…BET surface areas of the nanofibers were measured to be 66 m 2 /g (Ni 20 min), 32 m 2 /g (Ni 180 min), 221 m 2 /g (Ni 30% Cu 20 min) and 222 m 2 /g (Ni 30% Cu 180 min). All fibers were previously found to be highly amorphous [24], with little evidence of graphitic structure. The Ni and Ni-Cu samples both display significant peak narrowing and an overall increase in intensity after annealing, which indicates the microstructure has coarsened.…”

“…The furnace was ramped to final temperature over a 20 min period and processing was stopped after 1 h at reaction temperature. It was previously demonstrated [24] that catalytic activity was maintained from 1 h to at least 12 h reactions, and therefore catalyst deactivation is not a factor in overall growth rate. After the reaction was complete, samples were cooled under nitrogen.…”

“…The primary use of the catalysts presented here has been the creation of three-dimensional nonwoven nanofibrous carbon structures using the constrained formation of fibrous nanostructures (CoFFiN) process [40], and the fibers deposited from this catalyst have been successfully applied to generate mechanically robust carbon aerogel structures at centimeter scales [41]. The particular advantage is the long lifetime of the catalyst, as it has proven to maintain a constant deposition rate over a 12-h period [24].…”