Air perturbation-induced low-frequency inductive electrochemical impedance arc in proton exchange membrane fuel cells

Abstract

Proton exchange membrane fuel cells involve complex electrochemical processes. Electrochemical impedance spectroscopy is a suitable technique to study these reactions occurring with different kinetics with the ohmic, charge transfer and mass transport processes routinely observed from 1 kHz to 1 Hz. However, a low-frequency capacitive/inductive component (<1 Hz) has been discovered in standard and extreme conditions, while its origin is yet to know. Here, we demonstrate that imposing air perturbations of the frequency and amplitude ratio of the current density perturbations can induce a low-frequency inductive semi-circle. Such air perturbation enables the accurate detection of the polarization resistance with a low-frequency impedance and can reach steady-state conditions during the low-frequency electrochemical impedance spectroscopy measurements. Controlling the air perturbation amplitude and current density (0.2–1 A cm−2) dominates the state of low-frequency arc, and the presence of a threshold for the air perturbation amplitude is crucial for its formation. Our findings elucidate why the low-frequency component has not been systematically detected before, due to variations of the oxygen concentration at the electrode. Finally, these results propose an easy-to-implement and widely applicable strategy to observe the low-frequency arc, investigate the cell diffusion properties and monitor the oxygen concentration at the electrode surface.