Corrosion resistance of coated aluminum bipolar plates for proton exchange membrane fuel cells

Abstract

Aluminum is a very attractive material for bipolar plates in proton exchange membrane (PEM) fuel cells due to its low weight, excellent thermal and electrical conductivity, as well as good recyclability. However, to achieve the necessary low contact resistance and corrosion stability, a suitable surface coating is needed. In the present study, two different material systems were evaluated, electroless deposited NiP based coatings and high-power impulse magnetron sputter-deposited (HiPIMS) Ti based coatings. The addition of a 100 nm amorphous carbon (a-C) top-layer on the NiP and Ti based coatings was also evaluated. The electrochemical corrosion behavior of the coatings was evaluated in simulated PEM environments. Potentiodynamic and potentiostatic polarization experiments revealed that the HiPIMS Ti coatings performed better than NiP coatings. The addition of the a-C top-layer on the other hand was found to be detrimental to the Ti based coatings resulting in a corrosion current density of 3.6 μA/cm2. The opposite was observed in the case of the NiP based coatings where the addition of the a-C layer decreases the corrosion current thereby increasing corrosion resistance. Further analysis showed that defects in the coating as well as the presence of a Fe-Si rich particles in the Al substrate were the initiation points for the corrosion attacks to occur.