The study of trivalent chromium electrodeposition on metallic bipolar plates for fuel cells

• Main Authors: Shen,Shih-Yu, 沈詩瑜
• Other Authors: Ger, Ming-Der
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/58182504498252092076

碩士 === 國防大學中正理工學院 === 材料科學碩士班 === 99 === Abstract In this work, Cr-C coatings were deposited on Cu-based alloy bipolar plates of fuel cells to enhance their conductivity and corrosion resistance by electroplating. The coatings were characterized with surface morphologies and composition analyses. Moreover, potentiodynamic, and contact resistance measurements were conducted in simulated fuel cell environment. The SEM observation shows that some cracks exhibit in the coatings, and the coatings containing more defects possess poor corrosion resistance. EDS analyses represent that all of the coatings prepared in this experiment contain carbon element. The main constituents of Cr-C coatings are Cr7C3, Cr23C6, and chromium phases as examined by XRD, and parts of the phases are amorphous structure. The results of corrosion tests show that the corrosion resistance of Cr-C coatings prepared under various conditions are better than that of Cu-alloy substrate, and the corrosion current density of the Cr-C coatings on metallic bipolar plate are less than 1μA/cm2 of DOE target. Among the electrodepositing Cr-C coatings, the corrosion current density and corrosion potential of the specimen prepared at the conditions of 10 A/dm2 and 10 min is lower to 3.585 × 10 - 7 A/dm2 and -0.064 V, respectively, but contact resistance of the coating is higher than the DOE target due to surface conductivity of the coating being inferior. To improve conductivity of Cr-C coatings and reduce their contact resistance, the amounts of ammonium formate were increased in trivalent chromium bath in order to enhance carbon content of the coatings. The results showed that carbon content of the coatings is promoted, the contact resistance between the coatings and gas diffusion layer is reduced, and corrosion resistance of the coatings is improved. X-ray diffraction patterns showed that Cr23C6 and amorphous chromium phases are main constituents in the coatings and the intensity of chromium carbide peaks is increased as increasing the concentration of ammonium formate in trivalent chromium bath. The results of corrosion tests under the simulation environments of proton exchange membrane fuel cell showed that the corrosion resistance of the coatings prepared in higher concentration of ammonium formate is better than that of the original coatings. The maximum power density of single cell assembled with Cr-C coated Cu-alloy bipolar plates is 3 W/cm2. This result indicated that the Cr-C coated bipolar plates display inferior performance of single cell to graphite bipolar plates.