Different Gas Feeding Modes

Using the charge-transfer resistances of the cathode and anode obtained by Wagner et al. [22], the apparent exchange current densities were calculated as Code = 0.1 Acm 2. and i athode = 6, uAcin 2 The results indicated that the cathode 

As discussed above, if the exchange current density of anode hydrogen oxidation is i nMc =0,1 Acni 2 and that of the cathode oxygen reduction reaction (ORR) is 

In a H2/02 (air) fuel cell, in general, the spectra, i.e., the Nyquist plots obtained by EIS measurements, very often have three features, which are denoted as high-frequency, medium-frequency, and low-frequency. The high-frequency region of an impedance spectrum is associated with the internal ohmic resistance and the contact capacitance in the granular electrode structure of the membrane electrode assemblies, whereas the medium- and low-frequency regions represent the charge- 

Two impedance arcs, which correspond to two relaxation times (i.e., charge transfer plus mass transfer) often occur when the cell is operated at high current densities or overpotentials. The medium-frequency feature (kinetic arc) reflects the combination of an effective charge-transfer resistance associated with the ORR and a double-layer capacitance within the catalyst layer, and the low-fiequency arc (mass transfer arc), which mainly reflects the mass-transport limitations in the gas phase within the backing and the catalyst layer. Due to its appearance at low frequencies, it is often attributed to a hindrance by finite diffusion. However, other effects, such as constant dispersion due to inhomogeneities in the electrode surface and the adsorption, can also contribute to this second arc, complicating the analysis. Normally, the lower-frequency loop can be eliminated if the fuel cell cathode is operated on pure oxygen, as stated above [18], 

For the low-frequency arc, many studies and explanations have been published. Fieiie and Gonzalez [29] studied the effects of temperature, membrane thickness, and humidification conditions on the impedance response. They suggested that the low-frequency arc has two causes the effect of liquid water formed at the anode, which affects the transport of oxygen and the hydration effect, which limits the transport within the membrane. The relative weight of these two effects depends on the thickness of the membrane and the working conditions of the fuel cell. They 

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