Reversible Oxygen-Ion Storage for Solid Oxide Cells

In a rechargeable oxide battery (ROB) a solid oxide cell (SOC) is combined with a component that acts as storage for oxygen ions. The cell is operated at 800°C in turns as fuel cell and as electrolyser. Yet, there is no need for the delivery of fuel because of the integrated iron oxide base storage component. This material regulates the oxygen partial pressure at the fuel electrode in a range of approximately 10^-21-10^-18 bar, which at 800°C corresponds to water vapor to hydrogen ratios between 1:4 and 4:1.

However, repeated charging (electrolysis) and discharging (fuel cell mode) can result in coarsening of particles and external layer formation. Both effects are not desired because they decrease the overall surface and thus the reaction kinetics. Adding secondary oxides to the Fe₂O₃ base material can mitigate those degradation phenomena. In the present study the effect of additions of Al₂O₃, CeO₂, Mn₃O₄, Cr₂O₃, TiO₂, SiO₂, and MgO to the Fe₂O₃ base on the degradation properties is analysed. To this end, compacted samples are repeatedly oxidised and reduced in a laboratory furnace, where the conditions present in the ROB are simulated. Using X-ray diffraction and scanning electron microscopy it was found that among the tested oxides only MgO and Al₂O₃ could mitigate the layer formation and the particle coarsening to some extent.