Quantitative analysis of internal polarization dynamics for polymer electrolyte membrane fuel cell by distribution of relaxation times of impedance

Investigating and interpreting each internal polarization dynamics that occurs in the polymer electrolyte membrane fuel cell is significant. Traditional equivalent circuit model fitting by nonlinear least-squares relies on prior model assumptions and initial value selection of components. In this paper, the distribution of relaxation times methodology with powerful separating ability is applied to reveal a more precise analysis of polarization processes. First, the electrochemical impedance spectroscopy under a broad of operating conditions is carried out. Four polarization dynamics related to oxygen transfer, charge transfer of the oxygen reduction, proton transfer inside cathode ionomer, and interface contact process between catalyst layer and membrane (perhaps, including anode oxidation reaction) are effectively extracted. Then, a fourth-order equivalent circuit model established via distribution of relaxation times results is introduced to quantify the loss of each polarization process. Based on this, for the first time, the sensitivity of each polarization loss against operating conditions is analyzed by the multiple stepwise regression analysis, and its application on vehicular fuel cell system control is discussed. Afterward, the distribution of relaxation times is also first to explore the loss and variation trend of each polarization process under flooding, membrane drying, and air starvation fault, where each failure type contains at least eight test sequences. These efforts represent a comprehensive and systematic guideline for fuel cells using distribution of relaxation times, which can also guide the study of degradation mechanisms, optimization design of materials, and even other electrochemical energy sources.