Effect of Roughness of Electroplating Ni Layer on Carbon Film-Coated Stainless Steel Grown by Chemical Vapor Deposition

• Main Authors: Wei-Min Chang, 張威閔
• Other Authors: Shi-Kun Chen
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/76328876987347196732

碩士 === 逢甲大學 === 材料科學所 === 97 === Carbon film-coated stainless steel (CFCSS) has been evaluated as substitute for graphite bipolar plate in polymer electrolyte membrane fuel cell (PEMFC), due to its low-cost and small-volume. The carbon film was synthesized by pyrolysis of acetylene. Pyrolytic carbon molecules form graphite carbon layer through the catalysis of Ni layer deposited by sputtering. In this study, Ni layer was prepared via electroplating due to the low-cost and superior-throwing power. Ni strike solution was chose for deposition, and the current density and electroplating time was manipulated in range of 1 – 10 A/dm2 and 15 – 1200 second, respectively. Carbon film was then deposited deposits at 750 oC under C2H2/H2 mixed gas ratio of 1.5 by CVD process. Surface morphology of the Ni layer was characterized by field emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM). X-ray diffraction (XRD) was used to indentify crystal structure of the Ni layer. Morphology of the carbon film was analyzed by FE-SEM. Potentiostat was used to measure chemical stability of the carbon film. While thickness of the Ni layer fixed at 810 nm, the surface roughness (Ra) of the Ni layer was decreased from 31.9 nm to 15.7 nm with increasing current density of electroplating from 1 A/dm2 to 10 A/dm2. After CVD process, fibrous carbon layer was grown on the Ni layer. The fibrous carbon layer can not protect the metallic substrate from the attack of sulfuric acid. To obtain a continuous dense carbon film the Ra value of the Ni layer should be in the range from 15.74 nm to 18.41 nm. It appears that the surface roughness of the Ni layer play an important role for the structure and the resultant chemical stability of the carbon films. The highest value of Ecorr (1.8 VRHE) was obtained with Ra = 16 nm. The Ecorr value is even higher than that of highly oriented paralytic graphite (HOPG, 1.6 VRHE).