Study On Surface Modification Of Stainless Steel Used For PEMFC

Stainless steel is the most widespread investigated materials to substitute for traditional machined-graphite bipolar plates. However, the inefficient corrosion resistance can still inhibit its application as bipolar plate for PEMFC. The most effective way to enhance its corrosion performance is to employ surface modification technology. The chemical polishing for 304stainless steel is conducted in this thesis. Due to the fact that traditional chemical polishing systems have a series of disadvantages such as heavier pollution, lower safety, the trial experiment seeking an environmently friendly technique is conducted in this thesis. Through orthogonal experimental test, the optimal technique for H₂O₂-C₆H₈O₇ solution is obtained as follows: C₆H₈O₇ 1 %, H₂O₂ 10 %, Fe(NO₃)₃ 3 %, H₂C₂O₄5 %, polishing temperature 20-30℃and polishing time 180-240 s. This technique producing no exhaust emission, is a better way for 304stainless steel chemical polishing.For the sake of improving traditional electrochemical polishing, the optimal solution composition and operating technique are attained through orthogonal experimental test. The optimal electrochemical polishing is showed below: C₆H₈O₇ is 55-60 %, H₂SO₄ is 15-20 %, current density is 20 A/dm², the distance between cathode and anode is 10 mm, polishing time is 200 s and polishing temperature remains 40℃.In comparison with corrosion resistance of original specimen, a range of electrochemical measurements from potential dynamic curve, current-time curve and EIS spectroscopy are carried out. Additionally, other comparisons concerning the surface structure of the specimen are also conducted. All these comparisons justify the enhancement of corrosion resistance property of polished 304stainless steel by both chemical and electrochemical polishing.