Evaluation of Transient Voltage Behaviour During Load Changes in Automotive PEM Fuel Cells

Abstract

Polymer electrolyte fuel cells reach high efficiency and zero emissions even under highly dynamic loads. Power fluctuations, sudden load changes, start up and shut down procedures cause locally very high as well as very low voltages. These undesired voltage levels accelerate the degradation of the cells in terms of carbon corrosion, platinum oxidation and membrane decomposition. Experiments with single cells are capable to indicate, which conditions are most harmful to the cell. The voltage response during load steps shows characteristic under- and overshoots. The amount of these over- and undershoots are directly correlated to the amount of the extend of the load change. The shape and the relaxation time of the voltage curve are dependent on the operation conditions of the cell in terms of humidity, pressure and stoichiometry.