A simple physics-based equation for low-current impedance of a PEM fuel cell cathode

A solvable physical model for impedance of the cathode catalyst layer (CCL) in a PEM fuel cell is developed. The model includes reaction activation and oxygen transport in the CCL; the proton transport is assumed to be fast. The expression for the CCL impedance Z is derived and represented as a sum of the charge-transfer Zct and oxygen transport Zox impedances. Availability of analytical expression for Zox enables to suggest a simple equation for the total CCL impedance, which includes oxygen and proton transport losses. This equation accurately reproduces a much more cumbersome exact solution obtained in Electrochim. Acta, 147 (2014) 773. An expression for the summit frequency of the oxygen transport arc is obtained.