A Ce(Mn,Fe)O2 dense nanofilm as an improved active anode for metal-supported solid oxidefuel cells

Abstract

The application of a mixed ionic and electronic conductor, doped CeO₂, as a dense anode was investigated in this study. The mixed electronic and oxide ionic conductivity in CeO₂ was significantly improved through the double doping of Mn and Fe. Although the solid solubility limit of Mn was approximately 20 mol%, no impurity phase was observed at 30 mol% Mn when Mn was co-doped with 10 mol% Fe; this result suggests that the solubility limit of Mn was expanded through the addition of Fe. The nano-sized Fe- and Mn-doped CeO₂ (CMF) film was highly active toward the anode reaction despite its high density. In addition, the CMF thin film was effective in preventing Ni diffusion into the LaGaO₃ electrolyte film; CMF therefore exhibits bi-functional properties for solid oxide fuel cells with LaGaO₃ perovskite electrolyte films. Furthermore, the insertion of a CMF dense film between the Ni–Fe substrate and the LSGM (La_0.9Sr_0.1Ga_0.8Mg_0.2O₃) electrolyte resulted in a significant increase in the power density of the cell, particularly at intermediate temperatures. The maximum power density was ca. 3.0 W cm⁻² at 973 K and ca. 0.2 W cm⁻² at 673 K. The high power density of the cell was explained by the enhanced anodic activity. Compared with porous anodes, the nano-sized film showed a significantly lower overpotential because of the improved oxygen ion conductivity and charge-transfer steps. Therefore, the nano-sized CMF dense film described here can serve as a unique active anode material.