Abstract
In this study, uncertainties during the assessment of the electrochemical impedance spectrum of the polymer electrolyte fuel cell (PEFC) attributed to inductive artefacts at high frequencies and inductive loops at low frequencies as well as oxygen diffusion time constant are discussed. A validated impedance model represented as an equivalent electrical circuit of a PEFC allowed the simulation of the effect of inductive artefacts, inductive loops and oxygen diffusion time constant on electrochemical impedance spectroscopy (EIS) measurements represented in the Nyquist plot. This study considers EIS measurements reported in previous studies and provides an insight into the EIS measurements with positive imaginary components at high frequencies attributed to the intrinsic inductance of the measurement cables during EIS tests and at low frequencies attributed to electrochemical mechanisms (e.g. side reactions with intermediate species) during PEFC operation. In addition, an overview of overlapping mechanisms (charge transfer and oxygen transport resistances during the oxygen reduction reaction) on the PEFC impedance spectrum attributed to oxygen diffusion across the cathode catalyst layer is presented. EIS measurements with positive imaginary components and with overlapping effects could yield to ambiguities when studying or relating electrochemical mechanisms (ion conduction, capacitance, charge transfer and mass transport resistances) of the PEFC through a defined single frequency or a single measured value represented in the Nyquist complex-impedance plot.
Highlights
Polymer electrolyte fuel cells (PEFC) are electrochemical devices that convert the chemical energy of hydrogen into electricity during a redox process
This study has demonstrated that the assessment of Electrochemical impedance spectroscopy (EIS) measurements of polymer electrolyte fuel cell (PEFC) represented in the Nyquist plot could be misled by the presence of inductive effects or EIS measurements with positive imaginary components at high and low frequencies
Inductive effects at high frequencies attributed to the intrinsic inductance of the electrical cables during EIS measurements can be reduced by hardware manipulation e.g. twisting electrical cables or using low inductive cables [38] connected between the PEFC and the load
Summary
Polymer electrolyte fuel cells (PEFC) are electrochemical devices that convert the chemical energy of hydrogen into electricity during a (hydrogen-oxidation and oxygen-reduction) redox process. The interpretation of the physical processes of the PEFC through EIS measurements can be obscured as uncertainties during the assessment of EIS measurements can be attributed to artefacts (inductive effects) from the measurement hardware as well as to overlapping effects (different physical processes) on the impedance characteristics These uncertainties could yield to ambiguities when studying or relating electrochemical mechanisms (ion conduction, capacitance, charge transfer and mass transport resistances) of the PEFC through a single measured value of EIS measurements represented in the Nyquist complex-impedance plot. The aim of this study is to provide an insight into the issues and errors that EIS measurements with positive imaginary components, and with overlapping effects, can generate when estimating electrochemical processes (ion conduction, capacitance, charge transfer, diffusion mechanisms and side reactions during the ORR) in PEFCs through a defined single frequency or a single measured value in the Nyquist complex-impedance plot.
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