BEPPEL – Bipolar Plates for Fuel Cells and Electrolysers

Fraunhofer ISE is investigating measurement techniques to characterize metallic bipolar plates (BPP). Especially for metallic BPP the contact resistance to the gas diffusion layer and the electrochemical corrosion stability are important. For our characterization we use potentiodynamic and potentiostatic measurement methods. These electrochemical methods are supplemented by element analysis of the electrolytes with ICP-MS and SEM/EDX analysis of the surfaces of the BPP samples before and after aging.

A test set-up was developed to measure exactly the contact resistance between metallic bipolar plate and gas diffusion layer separately from the bulk resistance of the gas diffusion layer. Also, electrochemically aged samples can be characterized.

In many cases (and especially for high quality coatings) the so called corrosion current cannot be identified, as it cannot be separeted from other reactions. Nevertheless one can draw conclusions regarding the coating quality and compare different coatings by electrochemical measurements, if different methods are combined. The element analysis of electrolytes after potentiostatic measurements gives insights into the solved metals and therefore the corrosion of the different layers. Bipolar plates are aged at different potentials: at 0 V for simulating anodic conditions in a fuel cell, at 0.8 V for cathodic conditions and 1.4 V short-term to simulate start-stop situations. With SEM/EDX one can analyse the sample surface before and after aging and defects can be detected. With the help of cyclovoltammetry we can investigate which electrochemical reactions take place at which potentials. The change of the BPP, e.g. the generation of surface oxides, can be seen through contact resistance measurements.