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

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 plate. These plates are normally 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 feed rate, the plasma gas flow (Ar, N2 and H2) were systematically varied. Titanium powder (45 μm) was sprayed in absence of O2 to prevent the formation of TiO2-x, which would reduce the electronic conductivity of the coating. Dense layers of Ti were produced with high plasma enthalpy. XRD measurements revealed that the resulting coatings were pure α-Ti. The densest coating, deposited with 21.27 MJ kg-1, had a leak rate of 4.3 mbar l cm-2. A coating development on SS bipolar plates resulted in low corrosion currents, demonstrating the promise of a good application for PEM electrolysers with bipolar plates made of stainless steel.