Self-Organization and Electrochemical Properties of Metal and Alloy-Coated Carbon Nanotubes

• Main Authors: Yun-Wen Chou, 周允文
• Other Authors: Chien-Te Hsieh
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/66684800325652479786

碩士 === 元智大學 === 化學工程與材料科學學系 === 95 === In the present work, we propose an efficient method to fabricate metal particulates deposited on CNTs, which consists of the following steps: (a) implantation of acidic groups, (b) ionic interaction, and (c) heat treatment. In the self-organization nanostructure, the major formation mechanism is to utilize the strong interaction between metal ions and oxygen functional groups and the sidewall of carbon nanomaterials.The paper was divided into two parts: Part 1. The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with Ni nanoparticles was investigated. A surface modification technique enabled different Ni particle densities to coat onto the CNT surface, which was chemically oxidized by nitric acid. It was found that each nickel nanoparticle has an average size of 30–50 nm, and the Ni-attached CNTs still possessed a similar pore size distribution. Cyclic voltammetry measurements in 6 M KOH showed that the electrochemical adsorption and desorption amount of hydrogen is a linearly increasing function of the Ni loading. This enhancement of electrochemical activity was ascribed to a fact that Ni particle acts as a redox site for hydrogen storage, thus leading to a greater specific peak current. According to our calculation, the electrochemical capacitance of nickel nanocatalyst in KOH electrolyte was estimated to be the value of 217 F/g. Charge/discharge cycling demonstrated that the Ni-attached CNT electrode maintains fairly good cycleability during 50 cycles. Part 2. CNT decorated with bimetallic platinum/ruthenium nanocatalysts were fabricated to investigate their electrochemical activity in acid solution. These PtRu/CNT composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and N2 physisorption. The crystalline size of PtRu nanocatalysts generally decreased with Ru atomic ratio, i.e., form 4.34 nm to 2.77 nm. The specific surface areas and pore size distributions of PtRu/CNT composites were slightly altered after the PtRu deposition. Cyclic voltammetry measurements in 1 M H2SO4 and in 0.5 M H2SO4 containing 0.5 M methanol showed that Pt75Ru25/CNT electrode has the greatest activity in electrochemical adsorption and desorption of hydrogen, i.e., the ratio of electrochemical surface coverage: 84.6 %; the higher If/Ib value and lower onset potential. This enhancement of electrochemical activity was attributed to two possible reasons: (a) addition of Ru in the bimetallic catalysts leads to reduce the required potential for water electrolysis and thus the associated carbon oxidation; (b) the presence of Ru in the bimetallic alloys acts an important role in regenerating inactive Pt–COads sties.