Abstract

In proton exchange-membrane fuel cells, the compactness and composition of amorphous carbon (a-C) films directly affect the interface-induced degradation of a-C-coated metallic bipolar plates, but their roles and synergistic effects are ambiguous. In this study, by changing the working pressure, the compactness and composition of a-C are adjusted, and the relationship among the plasma state, microstructure, and performance of coated 316L stainless steel are studied. Results show that, at 2 mTorr, a high ionization degree of the plasma causes high compactness (highest density 2.52 g/cm3) and large sp2 cluster size in a-C films, resulting in their best performance. At 11 mTorr, the low ionization degree causes their loose structure and large sp2 cluster size. The possible galvanic coupling effect can result in serious interface damage and the highest Fe ions concentration of 13.05 ppm after a potentiostatic test. Thus, high compactness and large sp2 cluster sizes should be obtained simultaneously to improve their performance.