Can metallic bipolar plates with low-cost Cr/a-C coating withstand cell reversal events in PEMFCs? Post-coated vs pre-coated BPs

• Published in: Materials today energy 2023-03, Vol.32, p.101247, Article 101247
• Main Authors: Müller, M.-V., Schwämmlein, J.
• Format: Article
• Language: English
• Subjects: Accelerated stress testing; Carbon coating; Contact resistance; Corrosion effects; Manufacturing sequence
• ISSN: 2468-6069; 2468-6069
• DOI: 10.1016/j.mtener.2023.101247

The so-called cell reversal caused by H2 starvation during polymer electrolyte membrane fuel cell operation can lead to anode potentials >1.5 Vanode and thus to significant carbon corrosion in the anode catalyst layer. In this work, the influence of cell reversals on the electrochemical stability of low-cost Cr/a-C post- and pre-coating on metallic bipolar plates (BPs) was investigated in a vehicle application-oriented test cycle. While the electrical resistance of the BPs with the low-cost coatings increased after the tests, no impact on the H2/air polarization curves was detected in comparison to BPs coated with Au as reference. Nevertheless, surface changes of the carbon coatings were detected in regions of BP bends because of water accumulation. Further analyses showed that corrosion products from the chromium interlayer were detected. We therefore assume that the high electrochemical potential during the cell reversal events can only corrode the low-cost carbon coatings on the BP in the presence of water, while the overall degradation of the BPs regarding their electrical resistance was negligible compared to the performance loss due to anode catalyst layer corrosion. Furthermore, no significant difference of the degradation characteristics (metal ion leaching, anode catalyst layer thinning) was found regarding the coating sequence. [Display omitted] •Comparable H2/air performance after cell reversal of all coating types.•After ∼9 h of cell reversal the threshold E ≤ −1.8 Vstack is reached.•Interfacial contact resistances after the tests increase for the Cr/a-C coatings.•In areas with water accumulation the Cr/a-C coatings are damaged.•Corrosion products do not enter the catalyst coated membrane.