The bigger drop of open circuit voltage (OCV) for a degraded or damaged cell unit will make it consume the electricity generated by other cells of the solid oxide fuel cell stack to electrolyze the exhaust gas. In this article, the degradation behaviors of Ni-YSZ∕YSZ $(0.5mmthick)∕La0.6Sr0.4MnO3−δ$ cell sample caused by exhaust of hydrocarbon fuel were studied by solid oxide electrolysis cell method. $I‐V$ curve and impedance spectra measurements were carried out to investigate the polarization feature of the electrodes during power generation and electrolysis at $1000°C$ with gas mixtures of $H2–CO2$, $CO–CO2$, and $H2–H2O$ at the Ni-YSZ working electrode (WE) as well as oxygen at $La0.6Sr0.4MnO3−δ$ counterelectrode. In case of $H2–CO2$ couple, It was found that the increase of $CO2$ only depressed the OCV due to the increase of oxygen partial pressure $(PO2)$ at the WE side, and the characteristics of the cell were more influenced by the $H2O$ produced during power generation. In the case of $CO–CO2$, more CO produced during electrolysis would lead to the carbon deposition, which can result in the increase of polarization resistance by the reduction of the active site (triple phase boundary). In the case of $H2–H2O$ couple, the polarization contribution was different for both power generation and the electrolysis. The former likely contributed from concentration polarization since its nature of producing $H2O$, and the latter mainly contributed to the active site polarization as compared with that from concentration polarization due to its nature of consuming $H2O$.

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