Tailoring structural and electrochemical properties of vertical aligned carbon nanotubes on metal foil using scalable wet-chemical catalyst deposition

A scalable process for the synthesis of vertical aligned carbon nanotubes (VA-CNT) with precise control over structural properties is described. Direct growth on metal foils is achieved using a dip-coating step for the wet-chemical catalyst layer deposition and a subsequent chemical vapor deposition step for CNT growth. Two optimized Fe/Co and Fe/Mo 2-ethylhexanoate/2-propanol solutions are applied as precursors for the catalyst layer deposition and the influence of catalyst film thickness on resulting CNT film properties is investigated. The catalyst layer thickness can be controlled by the precursor salt concentration in the dip coating solution. By using a Fe and Co (2:3 ratio) catalyst, the CNT film homogeneity dramatically drops with lowered catalyst concentration due to a strong Ostwald ripening behavior of the catalyst layer. By using the FeMo (47:3 ratio) catalyst system. homogeneous VA-CNT films are obtained and the average CNT diameter can be adjusted in a range of 5-20 nm by the catalyst layer thickness. The electrochemical properties of the CNT electrodes are investigated in a symmetric supercapacitor test cell. The lowest CNT diameters of 5 nm results in a specific double layer capacitance up to 60 Fg(-1), while the density of the films directly correlates with its pore resistance. (C) 2012 Elsevier B.V. All rights reserved.