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An impedance separation analysis of the anode and cathode of a practical solid oxide fuel cell ͑SOFC͒ is conducted. Electrochemical impedance spectroscopy with a two-electrode setup is applied to an anode-supported intermediate temperature microtubular SOFC composed of a Ni/͑ZrO 2 ͒ 0.9 ͑Y 2 O 3 ͒ 0.1 cermet anode, a La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 2.8 electrolyte, and a ͑La 0.6 Sr 0.4 ͒ ͑Co 0.2 Fe 0.8 ͒O 3 cathode. Measurements are carried out for the cell operated at 700°C with varying flow rates and compositions of the H 2 /N 2 mixture gas fed into the anode and the O 2 /N 2 mixture gas fed into the cathode. The anode and cathode impedances are thereby separately assigned to low and high frequency impedance spectra, respectively. An equivalent circuit model is applied to the spectra to acquire the polarization resistances and associated capacitances for the charge and mass transfer processes at the anode and cathode and the cell ohmic resistance. The variation in these circuit parameters are then obtained in accordance with current densities and anode gas-feed conditions. In addition, the hydrogen diffusion length correlated with the Nernst loss in the axial direction of the anode substrate tube is estimated. These parameters obtained separately and simultaneously for each part of the cell are informative for a detailed analysis and diagnosis of practical SOFCs under operation.

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We have investigated the behavior of an operating polymer electrolyte fuel cell (PEFC) with supplying a mixture of carbon monoxide (CO) and hydrogen (H2) gases into the anode to develop the PEFC diagnosis method for anode CO poisoning by reformed hydrogen fuel. We analyze the characteristics of the CO poisoned anode of the PEFC at 80°C including CO adsorption and electro-oxidation behaviors by current-voltage (I‐V) measurement and electrochemical impedance spectroscopy (EIS) to find parameters useful for the diagnosis. I‐V curves show the dependence of the output voltage on the CO adsorption and electro-oxidation. EIS analyses are performed with an equivalent circuit model consisting of several resistances and capacitances attributed to the activation, diffusion, and adsorption∕desorption processes. As the result, those resistances and capacitances are shown to change with current density and anode overpotential depending on the CO adsorption and electro-oxidation. The characteristic changes of those parameters show that they can be used for the diagnosis of the CO poisoning.

The present study was carried out to find out the best combination of gas diffusion layers (GDLs) for a polymer electrolyte fuel cell (PEFC) operated under very low-humidity conditions at the cathode and high-humidity conditions at the anode using a test apparatus in which the clamp pressure on the cell could be accurately controlled. For cathode GDLs, it is important to maintain humidity and prevent dehydration of the MEA. A microporous layer (MPL) coating on the low-porosity carbon paper substrate is effective for enhancing PEFC performance. For anode GDLs, however, it is important to increase water transport from the humidified hydrogen gas to the MEA. An anode GDL with the MPL reduces PEFC performance. Hydrophobic treatment by PTFE (polytetrafluoroethylene) loading in the anode GDL is effective for performance enhancement. However, when the PTFE content becomes too high, the water transport properties are reduced, thereby lowering PEFC performance.