Preparation and electrochemical properties of ${\hbox{N}}{{\hbox{d}}_{{{2} - x}}}{\hbox{S}}{{\hbox{r}}_x}{\hbox{Fe}}{{\hbox{O}}_{{{4} + \delta }}}$ cathode materials for intermediate-temperature solid oxide fuel cells

Abstract

Cathodic materials ${\hbox{N}}{{\hbox{d}}_{{{2} - x}}}{\hbox{S}}{{\hbox{r}}_x}{\hbox{Fe}}{{\hbox{O}}_{{{4} + \delta }}}$ (x = 0.5, 0.6, 0.8, 1.0) with K₂NiF₄-type structure, for use in intermediate-temperature solid oxide fuel cells (IT-SOFCs), have been prepared by the glycine–nitrate process and characterized by XRD, SEM, AC impedance spectroscopy, and DC polarization measurements. The results have shown that no reaction occurs between an ${\hbox{N}}{{\hbox{d}}_{{{2} - x}}}{\hbox{S}}{{\hbox{r}}_x}{\hbox{Fe}}{{\hbox{O}}_{{{4} + \delta }}}$ electrode and an Sm_0.2Gd_0.8O_1.9 electrolyte at 1,200 °C, and that the electrode forms a good contact with the electrolyte after sintering at 1,000 °C for 2 h. In the series ${\hbox{N}}{{\hbox{d}}_{{{2} - x}}}{\hbox{S}}{{\hbox{r}}_x}{\hbox{Fe}}{{\hbox{O}}_{{{4} + \delta }}}$ (x = 0.5, 0.6, 0.8, 1.0), the composition ${\hbox{N}}{{\hbox{d}}_{{{1}.0}}}{\hbox{S}}{{\hbox{r}}_{{{1}.0}}}{\hbox{Fe}}{{\hbox{O}}_{{{4} + \delta }}}$ shows the lowest polarization resistance and cathodic overpotential, 2.75 Ω cm² at 700 °C and 68 mV at a current density of 24.3 mA cm⁻² at 700 °C, respectively. It has also been found that the electrochemical properties are remarkably improved the increasing Sr content in the experimental range.