Internal polarization process revelation of electrochemical impedance spectroscopy of proton exchange membrane fuel cell by an impedance dimension model and distribution of relaxation times

Electrochemical impedance spectroscopy (EIS) is a widespread non-invasive technology applied in proton exchange membrane (PEM) fuel cell characterization and diagnosis. In an experimental impedance plot, multi-arc nature displays or some arcs may merge. To fully reveal the internal polarization process inside the fuel cell, a two-dimension impedance model involving dominant transient behaviors such as electrochemical reaction, reactant transfer, and membrane water transfer is used for impedance spectroscopy calculation. An independent impedance analysis methodology by configuring system dynamics is utilized to demonstrate the physical nature of different frequency features. Meanwhile, a model-free approach to the distribution of relaxation times (DRT) helps probe the characteristics of different time constants in the impedance spectroscopy. A systematic dynamic configuration and model parameter independence analysis supports the assignment that polarization processes in the impedance spectroscopy from ultra-high frequency to ultra-low frequency correspond to anode chemical reaction, proton transfer inside the ionomer of the cathode, charge transfer attributed oxygen reduction reaction, oxygen transfer in the cathode, and dissolved water transfer. In detail, the results indicate that membrane water content affects the conductivity of the polymer, in turn determining proton transfer and charge transfer loss. Besides, oxygen molar concentration along the channel strongly influences whole mass transfer loss, followed by concentration in the gas diffusion layer. The inductive loop caused by membrane hydration is mainly determined by the gradient and net diffusion flux of the dissolved water across the membrane. These works provide a deep insight into impedance behaviors and help material optimization and controller design.