Starvation, flooding, and dry‐out phenomena occur in polymer electrolyte membrane fuel cells (PEMFCs), due to heterogeneous local conditions, material inhomogeneity, and uneven flow distribution across the single cell active area and in between the individual cells. The impact of the load level and air feed conditions on the performance was identified for individual single cells within a 10‐cell stack. Analysis of the current density distribution across the active area at the cell level was correlated with electrochemical impedance spectroscopy to enable operando fault diagnostic without any impact of the applied analytical tools on the single cell behavior. Moreover, the combination of both technologies allows in‐depth analysis of fault mechanisms in fuel cell single cells with improved sensitivity. Current density distribution and the quantitative assessment of the performance homogeneity demonstrated high sensitivity to small humidity changes and allow the detection of critical events, such as dry‐out in single cells. Impedance analysis is more sensitive regarding polarization and diffusion limitations and allows detection of cell flooding. The combination of both techniques is required for reliable identification of air starvation faults.

The dynamic impedance analysis of direct methanol fuel cell (DMFC) cathode supplied with pure oxygen is presented. Presented results were obtained during dynamic changes of the current density in working fuel cell. Investigation of the occurring processes at cathode was carried with dynamic electrochemical impedance spectroscopy (DEIS). A discussion was conducted based on the determined correlation parameter χ². It was shown that the selection of an appropriate equivalent circuit cannot be carried out only with correlation parameter of analysis between experimental impedance spectra and the equivalent circuit. Comprehensive analysis of equivalent circuit parameter changes during fuel cell working is needed to determine appropriate equivalent model. Thanks to DEIS technique, comparing of the different equivalent circuits proposed in other works during dynamic changes of operating condition could be presented. In addition, the new electrical circuit has been proposed to describe the cathode performance with poisoned electrocatalyst in fuel cell with reduced efficiency.