Carbon nanostructures: A morphological classification for charge density optimization

Nanostructured carbons offer great promise in numerous electrode applications due to their high surface area and area specific capacitance. With the growing importance of energy applications in particular, a need has emerged to characterize the various forms of activated and nanostructured carbons in the context of their electrochemical charge-storage capacity. However, the use of gravimetric or area specific capacitance can be uninformative or even misleading due to the critical role of exposed linear edge density on charge-transfer processes; edges exhibit approximately 20x greater specific capacitance than basal planes. Thus, a more robust normalization is needed for materials that possess this extreme anisotropy. By classifying nanostructures based on linear edge density, a deeper understanding of materials performance can be obtained and a more informed comparison of nanostructures is enabled. This report provides a classification of carbon nanostructures based on the dimensional organization of their edge structures. Morphological benchmarks of the classification are provided, including a novel graphenated CNT hybrid which increases the linear edge density of nanostructured carbons by an order of magnitude. Geometric consideration of the dimensional nature of the edge organization enables quantification of the edge density per unit nominal area. (C) 2012 Elsevier B.V. All rights reserved.