Estimation of Water Layer Thickness Adjacent to the Cathode Catalyst Layer of a PEFC (Analysis Using Electrochemical Impedance Spectroscopy)

Abstract

We have analyzed the impedance of the cathode of a polymer electrolyte fuel cell (PEFC) to estimate oxygen diffusion distance, d. Assuming planar oxygen diffusion in a thin liquid water layer at the cathode unconventionally, we can regard d as water layer thickness adjacent to the cathode catalyst layer. Calculated values of d agree well with our previous experimental result of liquid water accumulation amount at the cathode. Measurement of impedance variation with time reveals that d initially tends to be almost constant with time after start-up from dry condition, but that excessive water accumulation due to long time operation causes an increase in d. From the viewpoint of the diagnosis, an exceeding increase in d can be used to indicate the flooding at the catalyst layer.