Low frequency inductive loop in EIS measurements of an open-cathode polymer electrolyte fuel cell stack. Impedance of water vapour diffusion in the cathode catalyst layer

Abstract

• Analysis of inductive loops in EIS measurements of an open-cathode PEFC stack. • Impedance model to predict inductive loops in PEFC-EIS measurements. • Inductive loops associated to water vapour diffusion in cathode catalyst layer. • Relation between trend of inductive loops and phase angle in EIS measurements. In this study, an impedance model of a polymer electrolyte fuel cell (PEFC) is considered to simulate inductive loops at low frequencies from electrochemical impedance spectroscopy (EIS) measurements carried out in an open-cathode PEFC stack. The new impedance model proposed in this study is derived from the hypothesis that water vapour transport in the cathode catalyst layer (CCL) yields the formation of inductive loops at low frequencies. The impedance model of the PEFC considers the impedance model of the CCL reported in a previous study and considers an analytical expression for the impedance of water vapour diffusion in the CCL. The developed PEFC impedance model is validated with EIS measurements featuring inductive loops at low frequencies and carried out in the individual cells comprising an open-cathode PEFC stack at two current densities. The parameters related to the impedance of water vapour diffusion simulate the inductive loops at low frequencies and simulate a change of the size of the impedance spectrum of the PEFC. Therefore, the formation of inductive loops at low frequencies can be attributed to not only water vapour transport, but also ionomer swelling/shrinking (hydration/dehydration) in the CCL. The impedance model can provide an insight into the relation between the trend of the inductive loops at low frequency and the change in the phase angle in the EIS measurements which can indicate the hydrated state in the membrane-electrode assembly of the individual cells of the open-cathode PEFC stack.