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An electrochemical impedance model is developed to describe the impedance response of a volumetric electrode accounting for proton migration in the absence of oxygen transport limitation. It is used to fit experimental impedance spectra in H2/O2 configuration in order to estimate the protonic resistance of the electrode. Spatial resolution is achieved using a segmented cell, in dry, partially humidified and fully humidified conditions and at different cell currents. The local effective humidity in the cathode catalyst layer (CCL) and in the membrane are deduced from a correlation relating the protonic resistance measured in H2/N2 configuration to the relative humidity. Self-humidification of a cell operated in counter flow with dry oxygen is monitored using this technique, and the contributions of the membrane and of the CCL to the overall ohmic losses are eventually estimated. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental results on the preparation and the electrochemical characterization of PtxCoy electrocatalytic particles with homogeneous composition, modeled by Franco et al. [J. Electrochem. Soc., 156, B4l0 (2009)]. Preparation is made through the direct liquid injection metallorganic chemical vapor deposition technique previously developed at CEA, and electrochemical analysis is carried out by using a rotating disk electrode and membrane-assembled gas diffusion electrode. Degradation structural changes are characterized by using transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Optimal Co compositions are identified for better oxygen reduction reaction activity and durability, validating the modeling studies. [ABSTRACT FROM AUTHOR]