Solid-Oxide Rechargeable Fe-Air Battery Using Fe Modified with Cr-Ni-PrBaMm2O5 for Low Temperature Operation
Authors: Kim Hackho , Ida Shintaro , Ishihara Tatsumi 
Published: February 2020

Recently, rechargeable battery with large capacity is strongly required for storage electric energy from wind or solar cell power generator. For this purpose, Sodium-surfer (Na-S) battery and redox flow battery are now considered because of the high capacity and efficiency. However, Na-S battery has disadvantage of safety issues because molten Na and S are used. On the other hand, redox flow battery is low energy density. On the other hand, iron is non-toxic, highly safety, and rich in natural resource and compatible for environment. So, solid oxide Fe- air battery is also highly interesting for large scale battery for energy storage. Fe-air solid state rechargeable battery was studied by several groups and this battery is consisted of reversible solid oxide fuel cell and redox media consisting of Fe. By using H2/H2O as a redox mediator, high cycle life is expected. However, up to now, operating temperature of the cell is as high as 1073 K because Y2O3 stabilized ZrO2 is widely used. In our previous study, we investigated the solid state Fe-air battery using LaGaO3electrolyte and reasonable charge and discharge property was demonstrated at 873K.
In this study, in order to operate the cell at lower temperature than 773 K from efficiency, catalyst used for Fe oxidation and reduction was investigated and it was found that Fe oxidation can be occurred at much lower temperature by mixing Ce0.6Mn0.3Fe0.1O2 (CMF) and the capacity of 600 Ah kgFe
-1, was achieved at 673 K by using CMF mixed Fe powder. However, the capacity is 50% of theoretical capacity and also decreased with cycle number of charge and discharge. Detail analysis of internal resistance suggests that overpotential of fuel electrode became larger with increasing cycle number. In particular, diffusion resistance of the fuel electrode is much increased suggesting that the aggregation of Ni-Fe particle is occurred. Since aggregation of Fe in Ni-Fe fuel electrode seems to be main reason for decreased discharge capacity, Ni mixed with Sm doped CeO2 was applied for fuel electrode. It was found that the cycle stability of charge and discharge was much increased when Ni-SDC was used for anode and discharge capacity of 600 Ah kgFe
-1 was stably sustained over 30 cycles. In spite of small degradation of the cell when H2 is used for fuel, discharge potential was still slightly decreased with cycle number and this may suggest that H2 formation rate by oxidation of Fe decreases with cycle number. So, in this study, optimization of catalyst mixed with Fe as energy storage media was further investigated for increased cycle stability of solid state Fe-air battery using LaGaO3based oxide electrolyte.
Among the catalysts investigated, stable cyclic redox property of Fe powder was achieved by mixing Cr, Ni, and PrBaMn2O5(PBMO). Fe powder with Cr and Ni and PBMO has high redox rate, stability and high oxidation degree and stable redox property was sustained over 50 cycles at 673 K. By applying Fe powder modified with Cr, Ni, and PBMO, the cell shows reasonably large discharge capacity and stable cyclability.
This study reveals that combination of reversible SOFC with Fe modified with 5 wt% Cr-1.5 wt% Ni-1.5 wt% PBMO as an energy storage media is a new type of battery with large capacity.