Electrochemical Improvement of the MWCNT/Al Electrodes for Supercapacitors.

Evgeny N Kabachkov,Arkady N Redkin,Eugene E Yakimov,Alena A Mitina

doi:10.3390/ma14247612

Abstract

An original technique of chemical deposition (CVD) by catalytic pyrolysis of ethanol vapor was used to directly grow multiwall carbon nanotubes (MWCNTs) layers on aluminum foil. The grown nanotubes had excellent adhesion and direct electrical contact to the aluminum substrate. This material was perfect for use in electrochemical supercapacitors. In this work, the possibility of a significant increase in the specific capacity of MWCNTs by simple electrochemical oxidation was investigated. The optimal conditions for improving the characteristics of the MWCNT/Al electrodes were found. Electrochemical treatment of MWCNT/Al electrodes in a 0.005 M Na2SO4 solution at a potential of 4–5 V for 20–30 min increased the specific capacity of MWCNTs from 30 F/g to 140 F/g. The properties of modified nanotubes were investigated by X-ray photoelectron spectroscopy, cyclic voltammetry (CV), and impedance spectroscopy. A significant increase in the concentration of oxygen-containing functional groups on the surface of MWCNTs was found as a result of electrochemical oxidation. The modified MWCNT/Al electrodes maintained excellent stability to multiple charge–discharge cycles. After 20,000 CVs, the capacity loss was less than 5%. Thus, the results obtained significantly expanded the possibilities of using MWCNT/Al composite materials obtained by the method of direct deposition of carbon nanotubes on aluminum foil as electrodes for supercapacitors.

Highlights

Numerous useful properties of carbon nanomaterials, such as a large specific surface area, low specific gravity, excellent chemical resistance, low cost and abundant supply of starting materials for their production, make them very attractive for widespread use in various fields of practical application [1,2,3]
A continuous homogeneous layer with an average surface mass of multiwall carbon nanotubes (MWCNTs) of 0.3–0.4 mg/cm2 was deposited on the surface of the aluminum foil
The MWCNT structure consists of many sp2-carbon basal planes (0001) which are visible in the tube image (Figure 1d) as a series of parallel lines with an average spacing of 0.36 nm

Summary

Introduction

Numerous useful properties of carbon nanomaterials, such as a large specific surface area, low specific gravity, excellent chemical resistance, low cost and abundant supply of starting materials for their production, make them very attractive for widespread use in various fields of practical application [1,2,3]. Carbon nanomaterials are often applied to promising energy sources [4,5,6] They are of particular interest for developing electric double layer capacitors (EDLCs) or supercapacitors, as their characteristics directly depend on the surface area of the working electrodes increased by carbon nanomaterials. In this regard, carbon nanotubes (CNTs) are of constant interest in this field of application, since they possess all the properties required (e.g., high specific surface area, low electrical resistance and chemical stability) for use in supercapacitors [7,8,9]. There have been methods reported [13,14,15,16] for achieving significant improvements in the characteristics of CNTs involving surface functionalization

Methods

Results

Conclusion