Corrosion resistance of Au/Ni thin films coated stainless steel used for a PEFC separator

Abstract

Recently, as a new clean and renewable energy much attention has been paid to the PEFC (Polymer Electrolyte Fuel Cell) because of energy and environmental problems, such as depletion of petroleum, global warming and so on. PEFC has the characteristics of a simple structure, easy to maintain and a low cost. One of the parts of the PEFC is called the 'separator'; metal separators have a major issue regarding compatibility with corrosion resistance and electrical conductivity, in addition to low cost. Using current technology, we have selected a stainless steel AISI316L with an Au/Ni skin film. Therefore, there is a need to make a thinner skin film especially an Au top film for suppressing the PEFC total cost. When thinking about skin film, defects in the Au top film increases gradually as the thickness of Au film decreases. As a result, intensive corrosion is generated due to defects in the Au/Ni skin film. However, there are few reports evaluating correlation between the corrosion characteristics of stainless steel with an Au/Ni skin film under a PEFC environment and existing defects in the Au/Ni skin film. Therefore in this study, the pinhole defect ratio especially in Au film was evaluated using the CPCD method. Au/Ni double layered coating was formed on AISI316L stainless steel employing the sputtering method because of its high adhesion strength. As the quasi-PEFC environment 1M H 2 SO 4 aqueous solution was selected and then the pinhole defect ratio was evaluated by the CPCD method. As a result, the pinhole defect area ratio of 80nm thick Au film was obtained to be about 1.1% in 1M H 2 SO 4 aqueous solution.