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In this study, the change of electrochemical parameters during the gradual water accumulation of a polymer electrolyte fuel cell (PEFC) are estimated using electrochemical impedance spectroscopy (EIS) measurements and an impedance model based on electrode theory during a two‐step oxygen reduction reaction (ORR). EIS measurements were carried out in a 5 cm2 H2/O2 PEFC operated under a dead‐ended configuration of the gas reactants and during gradual accumulation of water. Kramers‐Kronig evaluation demonstrated that the EIS measurements comply with stability and linearity properties and the inductive loops featured at low frequencies are attributed to electrochemical mechanisms within the PEFC and not to instability during gradual water accumulation. The impedance model has been reported in a previous study and simulates inductive loops at low frequencies which are attributed to platinum oxide formation during the ORR. The estimated parameters obtained from this EIS‐modeling analysis can provide an insight into the decrease in PEFC performance during flooding conditions. A further qualitative analysis considering the effect of long‐term water accumulation on the oxygen‐reduction charge transfer resistance is discussed. It is possible to have an insight into the physical mechanisms of the PEFC, by combining different experimental techniques and fundamental theory in a complimentary manner. [ABSTRACT FROM AUTHOR]

Abstract: In this article, water accumulation abnormalities in small‐scale lungs are numerically and experimentally studied at microwave regime. The noninvasive passive microwave sensing platform considered here comprises the use of two low‐profile patch antennas. The sensors, operating at the ISM band, are attached back‐to‐back to the skin surface of the lungs. By monitoring the sudden changes of computed transmission coefficient (both magnitude and phase) between the two sensors, qualitative measures can be developed to estimate whether significant water accumulation in lungs take place or not, which can provide further insights at an early medical diagnosis. Several numerical case studies are developed and studied here that mimic various water accumulation scenarios within the modeled lungs. A practical small‐scale yet low‐cost platform integrated with the microwave sensors was demonstrated and validated. The results correlate reasonably well with numerical results. [ABSTRACT FROM AUTHOR]