Titanium coatings deposited by thermal spraying for bipolar plates of PEM electrolyzers

Kurzfassung

Proton exchange membrane (PEM) electrolysers are promising systems for generating high purity hydrogen. One of the key components of these devices is the separator or bipolar plates. These are made of Ti since the passive layer of TiO2-x protects it against corrosion in the aggressive environment of a PEM electrolyser. Unfortunately, this metal is expensive and machining the flow channels is complicated. A more suitable material would be stainless steel (SS). However it corrodes when used for bipolar plates. Additionally Fe and Cr ions poison the membrane electrode assembly MEA of the electrolyser. Therefore, the SS bipolar plates have to be protected with a coating that is corrosion resistant in acid environment and conductive. In this work we produced Ti coatings on SS Crofer® 22 H substrates by vacuum plasma spraying (VPS) technique. Several parameters such as the type of nozzle, the powder feeder rate, the flows of Ar, N2, H2 and the temperature of the SS substrate were systematically varied. The Ti powder (45 µm) was sprayed in absence of O2 to prevent the formation of TiO2-x. This later reduces the electronic conductivity of the coating. Dense layers of Ti were produced with high H2 and low Ar flows, see Figure 1. XRD revealed that the resulting coatings were pure α-Ti. The densest coating, deposited with 12 and 30 slm of H2 and Ar respectively, had a leak rate of 2.6 mbar. Several modification to the layers resulted in very low corrosion currents thereby demonstrating the promise for electrolyser bipolar plate coatings. These layer modifications will be discussed in the contribution.