The reduction properties of M-doped (M=Zr, Gd) CeO₂/YSZ scaffolds co-infiltrated with nickel

In recent years infiltration of materials into porous ceramic scaffolds has been shown to be an effective way of creating catalytically active components for solid oxide fuel cells (SOFCs). However, the redox properties of these novel structures are not well understood. Here, we use X-ray photoelectron spectroscopy (XPS) and in-situ Raman spectroscopy to investigate the oxidation properties of yttria-stabilised zirconia (YSZ) scaffolds infiltrated with ceria (CeO₂), gadolinium-doped ceria (GDC) and zirconia-doped ceria (ZDC), with and without Ni. XPS shows that doping ceria with zirconia increases the ratio of Ce³⁺ to Ce⁴⁺, while gadolinium doping results in a decrease of Ce³⁺. The presence of Ni increases the Ce³⁺/Ce⁴⁺ ratio for CeO₂ and GDC, but had little effect on ZDC. We used the shift of the F_2g Raman peak to monitor in-situ, the oxidation state of ceria. In the as-made compounds, we show that while the gadolinium and zirconium dopants significantly change the oxidation characteristics of ceria, the resulting materials are only significantly reduced above 500 °C when co-infiltrated with Ni. In-situ Raman monitoring during reduction as a function of temperature showed that while ZDC reduces much more readily than undoped ceria or GDC, the presence of Ni dominated the reduction dynamics.