Application of complementary analytical tools to support interpretation of polymer-electrolyte-membrane fuel cell impedance data

A series of ex situ techniques, including scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and inductively coupled plasma-mass spectroscopy were used to study morphological and chemical changes associated with the aging of a membrane electrode assembly in a polymer-electrolyte-membrane fuel cell. These results were correlated with the results of in situ electrochemical measurements, including measurement of steady-state polarization curves and electrochemical impedance spectroscopy. The results support the premise that the low-frequency inductive features seen in the impedance response provide information useful for understanding phenomena, such as platinum oxidation, that lead to reduction of fuel cell performance. The reduction in electrochemically active surface area, obtained from the high-frequency part of the impedance response, was consistent with the observed agglomeration of platinum particles and platinum oxidation.

Research highlights▶ The interpretation of low-frequency inductive impedance spectroscopy loops in terms of platinum oxidation was confirmed. ▶ The amount of oxidized Pt in the near surface region of the catalyst was similar to the amount of oxidized Pt in a 3 ML PtOx film on a single crystal Pt surface. ▶ Reduction of electrochemically active area was inferred from the evaluation of interfacial capacitance. ▶ ICP-MS data showed trace amounts of Pt in the fuel cell effluent. ▶ Results support the premise that the low-frequency inductive features in the impedance response provide information useful for understanding the reduction of fuel cell performance.