Mechanisms of Molybdenum Doping for Enhancing Fluoride-Induced Pitting Corrosion Resistance in Titanium Alloys for PEMFC Bipolar Plates
摘要
Titanium alloy bipolar plates with excellent performance play a crucial role in improving the overall performance of proton exchange membrane fuel cells (PEMFC). However, the localized pitting corrosion induced by fluoride ions presents a significant limitation to the widespread application of this material. In this study, Mo-modified titanium alloy bipolar plates were synthesized using vacuum arc melting, and the mechanisms underlying the inhibition of pitting corrosion were elucidated. The results showed that the Mo is evenly distributed in titanium alloys and is concentrated in small amounts at grain boundaries, existing in 4-valent and 6-valent states. Further electrochemical results reveal that the Ti-Mo alloy have exceptional resistance to corrosion caused by fluorine. In anode environment, the corrosion current densities of the Ti-0.6Mo alloy anode are measured at 0.437 µA cm−2, while the constant potential current densities stay stable at − 0.786 µA cm−2, which is lower than that of Pure Ti (3.278 µA cm−2, 1.323 µA cm−2, respectively). It is worth nothing that the addition amount of Mo is 0.6 wt.%, a MoO3 phase is formed in the pitting holes, which can effectively inhibit the pitting of F−. (The work function of MoO3 is 8.221 eV.) In addition, Ti-0.6Mo demonstrates good interfacial contact resistance under a compressive force of 140 N cm2 (19.5 mΩ cm2). Although this does not meet the DOE's 2020 target of 10 mΩ cm2, it significantly reduces the challenge of subsequent coating modifications. This study elucidates the mechanism by which Mo inhibits pitting corrosion induced by F− ions in Ti-Mo bipolar plates, offering valuable insights for the modification of Ti-Mo bipolar plates.