Sung-Chul Kim1, Shin-ichi Yamaura1 Takanori Igarashi2, Yuta Shimizu2, Koji Nakashima2, Akihiro Makino1 and Akihisa Inoue1
1Institute for Materials Research, Tohoku University, Sendai 980-8577
In this study, the newly designed bipolar plates for proton exchange membrane fuel cells (PEMFC) were produced by the HVOF spray-coating the Ni65Cr15P16B4, Ni60Cr20P16B4 and Ni55Cr25P16B4 alloys on Al plates having a flow field. As a result of XRD observations, it was found that the HVOF spray-coated Ni65Cr15P16B4 and Ni60Cr20P16B4 alloy films deposited on Al plates showed mainly a broad hallo peak coming from the glassy matrix and a small peaks from the crystalline phases. The spray-coated Ni55Cr25P16B4 alloy showed sharp distinct peaks coming from crystalline phases. So, it was difficult to prepare the coating layer with single glassy phase by the HVOF spray-coating in this study.
The corrosion resistance of these Ni-Cr-P-B alloy films deposited by the HVOF-spray-coating was studied under simulated PEMFC environments. As a result, it was found that the corrosion current density of these films was smaller than that of the high-corrosion-resistant stainless steel SUS316L.
Then the I-V performance of a single fuel cell with these bipolar plates produced in this work was studied and we found that the single fuel cells with the alloy-coated bipolar plates showed high I-V performance as well as the cell with the carbon bipolar plates. Among them, the Ni60Cr20P16B4 alloy showed the highest I-V performance, showing the largest current density at 0.3 V. After that, the 24 h durability tests were conducted at the constant current density of 200 mA·cm-2. As a result, the cell voltage of a single fuel cell with the alloy-coated bipolar plates did not show significant voltage drop during the tests. It can be concluded that the most suitable alloy for bipolar plate prepared in this study is Ni60Cr20P16B4 alloy.
XPS analysis of the surface layer of the Ni-Cr-P-B alloy-coated bipolar plates was conducted after the 24 h durability tests. As a result, the Cr2O3 passive film was found in all the Ni-Cr-P-B alloy surface films and also the P2O5 in the Ni65Cr15P16B4 and Ni55Cr25P16B4 alloy surface films and Ni(OH)2 in the Ni65Cr15P16B4 alloy surface film. This observation indicates that the surface passive film of Ni60Cr20P16B4 alloy contains the Cr2O3 of the highest concentration among the three alloy surface films, resulting in the highest I-V performance and good durability.
proton exchange membrane fuel cell, metallic glass, bipolar plate, high velocity oxygen-fuel spray coating
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