Dynamic Operational Conditions

The dynamics of polymer electrolyte membrane fuel cells taking place in different time and spatial scales are discussed. First the processes taking place at the cell level are described, namely double layer charging, charge transfer and mass transport. In addition, transients associated with humidification of membranes and catalyst poisoning are examined. At the stack level, heat transfer and gas distribution determines the dynamics of fuel cells and the consequences are considered. Finally the system level encounters transient limitations due to different subsystems, in particular the fuel supply, the air supply, the heat management and the control of the system. A section describing the methods to measure and to determine dynamic processes focuses on the time domain and frequency domain responses of fuel cell and the corresponding methodology. Finally, selected experimental examples for different dynamic behaviours and measurements on all scales are presented