Cost Reduction of large scale PEM Electrolysers by New Electro-catalysts and Bipolar Plates

Kurzfassung

Hydrogen is expected to play an important role as energy storage media when produced from renewable energies such as solar or wind by using proton exchange membrane water electrolysis (PEMWE) systems. Key components of the PEMWE that determine the stack cost are the bipolar plates (BPP) and the high loading of electro-catalyst for the OER in state of art membrane electrode assemblies. This presentation will discuss the potentials for cost reduction by synthesizing supported IrO2 electro-catalyst replacing the corresponding unsupported electro-catalysts. The supports need to be highly stable and exhibit sufficient electronic conductivity. A suitable support candidate has been identified that provides superior performance compared to the Ir black electro-catalysts. A more suitable material for bipolar plates would be stainless steel (ss), which is cheaper and easier to machine than titanium. However, it corrodes dramatically when used in PEMWE. Additionally, the ions released from the corrosion process poison the catalysts coated membrane (CCM) of the electrolyzer. Consequently, the stainless steel has to be protected with a coating that is corrosion resistant in acid environment and conductive, at the same time. We have developed a titanium coating for stain less steel BPP of PEMWE. The technique of vacuum plasma spraying (VPS) was used for this purpose. The coating was physically and electrochemically characterized. The minimum thickness that can be achieved is 13.5 µm. After surface modification the coating has an interfacial contact resistance (ICR) of less than 10 mΩ cm2 under 140 N cm-2, which meets the DOE 2015 target for BPP of PEM fuel cells. Corrosion measurements were performed in simulated environment of PEMWE. Figure 2 presents the potentiodynamic polarization curves of the uncoated and coated stainless steel substrate (ss) with titanium (Ti/ss). The characteristic of Ti/ss was measured after a constant polarisation at 2 V vs. RHE for 24 h and neither corrosion of the ss substrate nor oxygen evolution on the sample was observed. Moreover, the current transients were highly dependent on the surface finishing of the coating but the protection offered to the substrate remained. XPS measurements showed that the oxidation of the coating occurs as a result of the anodization process in acid medium and not during the thermal spraying deposition. Given the superior characteristics of the coating, it might have a large impact on the cost of PEMWE systems for large scale electricity storage from renewables.