Elsevier

Materials Letters

Volume 85, 15 October 2012, Pages 40-43
Materials Letters

Nano iron oxide (Fe2O3)/carbon black electrodes for electrochemical capacitors

https://doi.org/10.1016/j.matlet.2012.06.109Get rights and content

Abstract

In this research, nano iron oxide (Fe2O3)/carbon black electrodes are prepared by mechanical pressing method and evaluated as possible electrodes for electrochemical capacitors. Electrochemical properties of the produced electrodes are studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests in 2 M KCl electrolyte at different scan rates. Scanning electron microscopy (SEM) is also used to characterize the microstructure and nature of the produced electrodes. Electrochemical stability of the electrodes is investigated by switching the electrode back and forth for 500 cycles at 20 mV s−1.The results obtained show a specific capacitance of as high as 40.07 F g−1 for 30:60:10 (carbon black:Fe2O3:polytetrafluoroethylene) electrode in 2 M KCl at 10 mV s−1. The proposed electrode exhibits good cyclic stability and maintains 80% of the capacitance after 500 cycles. SEM images confirm the porous structure of Fe2O3/carbon black electrodes.

Highlights

► Fe2O3/CB nanocomposite has been suggested as supercapacitors electrode material. ► 30:60:10 (CB:Fe2O3:PTFE) electrode has as high as 40.07 F g−1 specific capacitance. ► Electrodes show porous surfaces, improve charge storage and delivering capability. ► Cycling tests confirm reversibility and increase the resistance after 500 cycles. ► CV curves reveal a low current response on voltage reversal at high scan rates.

Introduction

Although the need for energy and energy storage will be far greater in the future, the problem of ensuring power quality is already upon us. Energy storage is being widely regarded as one of the potential solutions to deal with the variations of variable renewable electricity sources and it is the key to unlocking the door renewable energy. Among different energy storage systems, electrochemical capacitors store the electrical energy in interfaces formed at a solid/electrolyte interface. Positive and negative ionic charges within the electrolyte accumulate at the surface of the solid electrode and compensate the electronic charge at the electrode surface [1]. High cycle life, high life time, high energy efficiency ranging from 85% up to 98% and high self-discharge rate are some of the characteristics of supercapacitors [2], [3]. Today, many laboratories are actively engaged in development of well-known type of supercapacitors, viz., electrochemical double-layer, pseudo and hybrid supercapacitors, and most researches have been focused on the development of different electrode materials [4], [5].

The aim of this work is to fabricate nano Fe2O3/carbon black electrodes using mechanical pressing as a fast method. Then the products were evaluated as possible candidate electrode for electrochemical capacitors using cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy.

Section snippets

Experimental

Materials: High purity (>99%) nano iron oxide (Fe2O3) (<50 nm), nickel foil (99.99% with 0.125 mm thickness) and polytetrafluoroethylene (<2 μm) were purchased from Aldrich, USA. All other chemicals used in this study were purchased from Merck, Germany. In order to prepare the electrodes, the mixture containing different wt% Fe2O3 and carbon black (CB) and 10 wt% polytetrafluoroethylene (PTFE) was mixed well in ethanol to form a paste and then was pressed onto the nickel foil (25 MPa), which served

Results and discussion

Specific surface area and porosity are two important parameters to prepare high efficient electrodes for electrochemical capacitors. The morphology and the nature of the as-prepared electrodes were analyzed using SEM. As shown in Fig. 1, images show good dispersion of the nanoparticles on the surface of the electrodes. This increases the specific surface area and makes the surface of the electrodes porous. This porous surface greatly improves the charge storage and charge delivering capability

Conclusions

In summary, nano Fe2O3/carbon black is a good candidate electrode material for electrochemical capacitors at low scan rates. This is based on the good electrochemical performance observed in the potential range from −0.3 to 0.25 V (vs. SCE) in 2 M KCl electrolyte. The surface showed a porous structure that greatly improves charge storage and charges' delivery of electrode capability. It shows a pseudo-capacitance characteristic and low ratio of the outer charge to total charge (qO/qT) of 0.3.

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