Nanostructure Material for Supercapacitor Application
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ABSTRACT Transition metal nitrides and carbonitride materials were fabricated via sol-gel technology. The transition metal amides were sythesized by two methods: chemical route and electrolysis. The transition metal amides were then further polymerized, sintering to high temperature in an inert or reduced atmosphere. Transition metal nitrides and carbonitrides powders with surface area up to 160 m2/g were obtained. The resultant electrode material showed high specific capacitance as crystalline ruthenium oxide.
I. INTRODUCTION Capacitive energy storage devices based on double-layer capacitance, or pseudocapacitance, have a wide range of potential applications. Currently, these capacitors are being used as the power back-up for memory devices in electronic equipment or for electrical actuators. Because of their high energy, power densities and long cycle life, their potential applications include pulse power, bridge power, load leveling, and stand-by power. The potential power density and cycle life of electrochemical capacitors are 2 orders of magnitude higher than those of rechargeable batteries[l]. Studies have shown that the projected battery life could be extended as much as 10 times by power conditioning a battery in electric or hybrid vehicles [2]. The electrochemical capacitor possesses electrodes, electrolyte, and a seperator. Several types of electrode materials have been developed. Activated carbon or foam represents one type of electrode material. Typical capacitance obtained from a electric double layer is in the range of 20 - 40 i.tF/cm 2 [3]. Certain transition metal oxides such as RuO 2 and IrO2 possess pseudocapacitance. Pseudocapacitance arises from highly reversible reactions, such as redox reactions, which occur at or near the electrode surfaces. Capacitance of 150 - 200 p±F/cm 2 has been observed for RuO 2 films [4]. Recently developed ruthinum hydroxide shows even higher energy storage density[5]. The third type consists of metallic bodies which are mechanically or chemically etched to provide a roughened surface and high specific surface area. High surface area metal electrodes are limited by electrochemical stability. Metals are generally unstable in oxidazing environments, therefore their use is limited as to the positive, reducing electrode or anode. The fourth type contains metal nitride. Metal nitrides are, in general, conductive and exhibit pseudocapacitance. Especially molybdenum nitride is an exanple of high energy density.[6] Among these four types of electrode materials, nitride electrodes have the greatest potential for supercapacitor application due to a higher energy density than carbon and metal, similar energy density as crystalline RuO 2 and a low cost. In this paper, the sol-gel process developed in Chemat Tecnology, Inc. for fabrication of nitride electrode materials is discussed. Nitride based electrode material showed same the order of energy density with ruthenium oxide crystalline materials. The voltage window of the sol-gel prepared molybdenum nitride was 1 volt in sulf
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