Metal bipolar plates in polymer-electrolyte membrane (PEM-) fuel cells are mainly used in low volumetric, low weight applications like automotive or portable systems.
Because of the highly corrosive conditions inside fuel cells lifetime is a task of great importance for long-term operation. As corrosion resistant metals like Titanium or Gold are cost intensive they cannot be used as metal substrate or as coatings.
Thus, the Fuel Cell Research Centre is developing innovative multi-layer coatings which are free from precious metals. The development is realized in cooperation with PT&B Silcor GmbH, a company in the field of thin layer coatings. By employing physical vapour deposition (PVD) coatings on the basis of alternating chromium nitride and amorphous carbon layers are deposited onto cheap metals like aluminium (cf. figure 1). Parameters like the thickness of the single layers are balanced carefully in order to achieve a dense and homogenous coating that is corrosion resistant and still exhibits good electrical performance.
First results of this research project which was funded by the Federal Ministry for Economic Affairs and Energy will be presented at the 5th European PEFC & H2 Forum in Lucerne, Switzerland (15/06/30 – 15/07/03). A focus will be put onto aluminium substrates and the use of metal bipolar plates in portable applications that are powered by direct methanol fuel cells (DMFC).
The results proof the feasibility of the new coating. Characterization results of coated and uncoated samples made from aluminium 1050A alloy show that the corrosion potential of the coated samples moves 0.36 V to a more positive value compared to uncoated aluminium. The corrosion current density at -0.13 V vs. Ag/AgCl which represents a typical operating point in DMFC decreases more than two orders of magnitude (cf. figure 2). Hence, a significantly enhanced corrosion resistance can be expected.
Future work will focus on further improvement of the coating, especially on the enhancement of the electric conductivity. Because of the relatively high specific electric resistance of amorphous carbon this is a task that needs further development.
Moreover, the influence of the surface texture on the homogeneity of the coating and the wetting behaviour will be examined.
- Mikrosystems and fluid mechanics
- surface analysis
- Service: Cell component characterisation
