Redox cycling of Ni–YSZ anode investigated by TPR technique

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Effect of redox cycling on a Ni–YSZ anode prepared from 50 wt.% NiO and 50 wt.% YSZ was investigated by using temperature-programmed reduction (TPR), XRD and SEM techniques. XRD results showed that NiO was formed during re-oxidation. Both the XRD and TPR results depicted that the conversion of nickel to NiO depended on the re-oxidation temperature. The oxidation of Ni to NiO occurred quickly in the initial several minutes and then reached a quasi equilibrium. The TPR profiles tracing the redox cycling showed that it brought continuous changes in the NiO micro-structure at 800 °C, whereas at 600 °C it had only little effects on the reduction of NiO. Re-oxidation resulted in the formation of spongy aggregates of NiO crystallites. Redox cycling at 800 °C led to a continuous decrease in the primary crystallite size of NiO and a high dispersion of the Ni particles. A continuous expansion of the slice sample was observed in both of the oxidized and reduced states during the redox cycling at 800 °C, whereas this process did not occur during the redox cycling at 600 °C.