An n-type oxide Fe_0.5Mg_0.25Ti_0.25Nb_0.9Mo_0.1O_4-δ for both cathode and anode of a solid oxide fuel cell

An oxide electrode replacing Ni/YSZ anode for a solid oxide fuel cell (SOFC) is desirable to reduce the carbon deposition under carbonaceous fuel. If this oxide material can simultaneously work as cathode, it will increase the simplicity and stability of an SOFC stack as in a symmetrical SOFC. However, the current oxide electrodes for symmetrical SOFCs are mostly p-type oxides showing compromised conductivity in reducing atmosphere, dictating a thin anode to reduce the ohmic loss. On the contrary, an n-type oxide showing superior electronic conduction in anode chamber will allow a thick anode support, giving room to a thin electrolyte and cathode to reduce the ohmic loss and the diffusion-related loss on the cathode side, respectively. A novel material Fe_0.5Mg_0.25Ti_0.25Nb_0.9Mo_0.1O_4-δ (FMTNM) with cations distributed randomly, based on n-type FeNbO4, is studied as both cathode and anode for an SOFC. This material synthesized in ambient air was stable in Ar-5% H2 at 750°C and showed higher electrical conductivity in reducing atmosphere than in air. It was the first demonstration using an n-type oxide for both cathode and anode due to the conductivity arising from Fe²⁺/Fe³⁺ and Mo⁵⁺/Mo⁶⁺ transition.