Vertically Aligned and Tree-like Carbon Nanostructured for Electrode of Electrochemical Capacitors

Abstract

Vertically aligned and tree-like nanostructures of carbon are grown by using plasma enhanced chemical vapour deposition (PECVD) method using electron cyclotron resonance (ECR) plasma system. These nanostructures consist of a multiwalled carbon nanotube which is aligned perpendicular to the surface of the substrate with carbon films attached to it like “branches” of a tree giving the structure a tree like appearance. The thin film of these nanostructures is deposited in a ECR plasma system on a nickel seed layer with a microwave power of 500 W using acetylene and hydrogen gas in 2:1 ratios as the source gases, at a working pressure of 7x10-4 mbar in presence of a negative substrate bias of 200 V 1. As the material with its vertical alignment and tree-like morphology has a very high exposed surface area, this material was speculated to act as a high-performance electrode of electrochemical capacitors (EC) or supercapacitors. The unique three-dimensional morphology of the material gives a high surface area with less areal footprint of the material. The electrochemical performance of the material as electrode of EC has been studied by depositing the material of thickness 1 μm on circular stainless-steel substrates of diameter 12 mm (area 1.13 cm2). 1 M Na2SO4 solution in deionised water is used as the electrolyte for the EC with absorbed glass mat as the separator between the two nanostructured electrodes. The entire assembly is done inside Swagelok type cell for testing the electrochemical performance. The EC showed a specific capacity of 920 μF/cm2 (9.2 mF/cc) at a scan rate 0.1 V/s which is higher than the reported values for vertically aligned carbon nanotube.2–4 A rectangular cyclic voltammetry curve is observed even at a voltage of 1 V/s. The results indicate that this material is a promising candidate for electrode material of supercapacitor. References M. Ghosh and G. M. Rao, Carbon 133, 239–248 (2018).B. Hsia, J. Marschewski, S. Wang, J Bin In, C. Carraro, D. Poulikakos, C. P. Grigoropoulos and R. Maboudian Nanotechnology, 25, 055401(9pp) (2014)T. Chen, H. Peng, M. Durstock, and L. Dai, Sci. Rep., 4, 1–7 (2014).C. L. Pint et al., Carbon N. Y., 49, 4890–4897 (2011) Figure 1