Interfacial Contact Resistance of Tantalum Coated Construction Materials for High Temperature Steam Electrolysers and Fuel Cells

Membranes e.g. Aquivion and Nafion doped with phosphoric acid are typically used in PEM systems at elevated temperatures. Thus the electrodes and bipolar plates should be resistant to this acidic environment. Due to high operating potential combined with the presence of oxygen, corrosion is particularly severe in the anode compartment of electrolysers. When the metals corrode, the passive films formed on the surfaces may increase the contact resistance and reduce cell performance. To overcome the corrosion problems we typically employ tantalum coated stainless steel as anode material. This work concerns the interfacial contact resistance (ICR) at the current collector/bipolar plate and current collector/catalyst layer interfaces, which contributes to efficiency losses of the cells. A way to reduce the ICR is by application of a corrosion resistant and electrically conductive coating. Bulk tantalum and tantalum coating on stainless steel are evaluated. Measurements were furthermore performed on titanium, since this is the most commonly used material for bipolar plates in Nafion based systems.