Distribution Study of Species and Current Density During Oxygen Starvation

In a fuel cell system the stack is strongly coupled with the main system components, among which the compressor is one of the most important. Malfunction of this auxiliary device (delay during peak power, low stoichiometry operation, emergency stop, etc) is directly responsible for bad oxygen distribution in the cathode (substoichiometry reactants feeding). This phenomenon is usually called oxygen starvation. In this study we want to identify the consequences of oxygen starvation on performance and durability of PEMFC stacks and more particularly on the current distribution along the cell. The oxygen concentration decreases along the channel and induces a change of the local electrochemical response; it means that the local current density on the cell is redistributed on the surface. This bad distribution of reactive gas (in a transient time or long time) decreases performance but may also have an effect on cathode degradation like carbon corrosion and platinum dissolution/oxidation. The current distribution along the cell is studied by two approaches (modeling and experiments). The local current is computed by measuring the local induced magnetic field and using Maxwell equations. The experiments are performed with a bi-cell stack developed by CEA with specific design for the magnetic sensors. The 3D model using serpentine bipolar plate meshing is adapted to dynamically compute the catalyst layer local conditions (local current, temperature, gases partial pressure, water activity). It is able to reproduce the conditions of low or high oxygen concentration in the cathode side.