In situ EIS data are presented on the anodic process in proton exchange membrane (PEM) fuel cells and the influence of CO poisoning of the Pt gas-diffusion electrodes (GDE) is examined. A characterization of the effects of interfacial kinetics in determining polarization losses in the presence of CO is performed by comparing impedance patterns obtained for cells of the type H 2 /H 2 with H 2 /(H 2 ϩ CO). The impedance spectrum of the poisoned electrode is strongly dependent on potential and on the CO concentration in the gas feed. In the range between 0 and 0.3 V the impedance increases rapidly with the potential, while at potentials higher than 0.3 V a "pseudoinductive" behavior is observed, in which a positive loop at higher frequencies is accompanied by a low frequency (LF) loop in the fourth quadrant. The latter was assigned to a new rate-determining process, the oxidation of CO ads by Pt-H 2 O ads . As a critical potential V crit is attained, the diameters of the two loops become almost equal and the LF limit of the impedance (R o ) approaches the value for unpoisoned electrode, showing that the activity of the electrode activity has been restored. The value of V crit is 0.43 and 0.58 V for electrodes poisoned with 100 ppm and 2% CO, respectively. At very high potentials, where the oxidizing species are Pt-OH ads , the impedance pattern is reversed to the second and third quadrants. Stripping voltammetry and polarization curves recorded in situ, are used to support the conclusions obtained from impedance measurements.

First-order reversal curve diagrams have been used to investigate magnetostatic interactions and average coercivity of individual wires in soft ferromagnetic uniform length nanowire arrays. We present a method for identifying these physical parameters on the out-of-plane first-order reversal curve diagrams: the position of the irreversible part on the critical axis is a good approximation to the average value of the nanowire coercivity and the maximum interaction field is equal to the interaction field at saturation. Their dependence upon material (CoFeB and Ni) and nanowire length are presented. The magnetostatic interactions increase linearly with length, in agreement with a model developed previously. The global array coercivity, obtained from magnetization curves, is generally lower than the apparent average coercivity for individual nanowires. This coercivity reduction increases linearly with the magnetostatic interactions. The general shape of the out-of-plane first-order reversal curve diagrams is compared with those obtained from a theoretical moving Preisach model.

An effective field model based on intrawire and interwire dipolar interactions has been developed in order to describe the magnetic anisotropy in arrays of homogeneous and multilayer nanowires. Variable angle ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) characterization techniques were used to determine the effective interaction field acting on Ni, CoFeB, and Ni/Cu nanowires. FMR spectra are well described by a rigid magnetization model and VSM data are in rough agreement with a mean longitudinal field model. FMR and VSM values of the effective fields are mutually consistent and in fair agreement with the values calculated with the model. The results show that the anisotropy of our arrays is strongly dominated by the dipolar interactions.

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