Real Time Water Detection for Adaptive Control Strategy in Pemfc-systems

Water content is well known as one key issue in operation of PEM-fuel cells. Due to the fact that the fuel cell produces water the output air stream is nearly saturated. That leads to a typical measurement range of humidity from 90 up to 100%. Sensor based water detection at that level is costly from technical and economical points of view. For that reason the aim of this project is to detect and balance the humidification state in real time by impedance spectroscopic measurements. Based on this measurement method with the help of defined variation of the operation conditions, significant measurement points which are sufficient for the characterization of the current humidity state have been selected.As the requirement of a fast and load independent measurement cannot be fulfilled by the conventional EIS, two methods have been implemented: reduced and fast electrochemical impedance spectroscopy (R-EIS and F-EIS). Both methods result in the secant angle of the Nyquist plot and Zreal, where latter is closely linked to the membrane resistance Rmem. The combination of these parameters correlated with their temporal change lead to a reliable humidity state indicator (HSI), which is used as input parameter for a real time control.