In order to elucidate the grooving corrosion suppression mechanism of Cu and Ti added ERW steel pipes, welded portions were immersed in salt water after polishing without using the SPEED method, which electrolytically polishes the specimen using a non-aqueous electrolyte. Sulfides were observed using FIB processing. Before immersion, MnS and Ti₄C₂S₂ were observed. After immersion, Cu_7.2S₄ precipitated on the MnS on the immersed surface. Furthermore, Ti₄C₂S₂ did not dissolve. Addition of Ti produced insoluble Ti₄C₂S₂, which reduced the number density of MnS, and addition of Cu precipitated insoluble Cu_7.2S₄ on MnS, suppressing the dissolution of MnS.

It has been pointed out that when stainless steel bipolar plates are used in PEFC, metal ions eluted due to corrosion contaminate the MEA and degrade cell performance. However, it was not clear whether the contamination mainly occurs from the anode side or the cathode side. In this study, a single cell was operated using bare type 304 stainless steel bipolar plates in contact with MEA and the cross sectional distribution of iron, chromium and nickel in the MEA was analyzed by ToF-SIMS. The results showed that iron, chromium and nickel were enriched in the anode side GDL and CCM. These results indicated that the leaching of metal ions from the anode side stainless steel bipolar plate was the main cause of MEA contamination.