Oscillation of PEFC under Low Cathode Humidification: Effect of Gravitation and Bipolar Plate Design

Kurzfassung

Oscillatory fluctuations of a single proton exchange membrane fuel cell appear upon operation with a dry cathode air supply and a fully humidified anode stream. Periodic transitions between a low and a high current operation point of the oscillating state due to the balance of drying and wetting processes in combination with water transport have been observed before and several new aspects are investigated. Oscillations are present under both galvanostatic and potentiostatic conditions and it is shown that the transitions involve local membrane drying by comparison of impedance data with current density distributions. The oscillations are caused by periodic flow type changes from one to two phase flow in the anodic channels of the flow field. It has been observed that cell orientation with respect to earth’s gravity field influences the liquid water distribution in the anodic flow channels and thus it is also affecting the oscillatory behavior of the cell performance. Comparing cell performance oscillations with a five channel serpentine flow field to a cell with one channel serpentine it is found that the oscillating performance behavior is also influenced by the gas velocity within an anodic flow channel.