Optimization of Ni–Fe exsolution in Sr0.93(Ti0.3Fe0.63Ni )O3−δ electrodes: Influence of reduction temperature on hydrogen oxidation reaction kinetics

Abstract

Exsolution of metallic nanoparticles (NPs) in perovskite oxides is an increasingly important strategy to enhanceelectrode performance in solid oxide cells (SOCs) technology. The question of which are the best reductionconditions to obtain an optimal exsolution treatment naturally arises. A second closely related question is on howexsolution features, such as nanoparticle size, density, or composition, influence the electrode’s reaction kinetics.In this work, we focus on the comparison between two different reduction temperatures, 700 ◦C and 750 ◦C, onthe exsolution process from a Sr0.93(Ti0.3Fe0.63Ni0.07)O3-δ (STFN) perovskite. We found that this reduction conditionsyield a highly different NP density, with the STFN-r700 presenting more NPs of smaller size, but therewere no significant differences on other parameters such as NP composition (~75 %Ni–25 %Fe), or on theremaining perovskite conductivity. Electrochemical impedance spectroscopy (EIS) measurements, analysed usingdistribution of relaxation times (DRT), reveal that the polarization resistance of STFN-r700 is substantially lowerthan that of STFN-r750. The improvement is particularly evident in the mid- and low-frequency processes, whichare associated with H2 adsorption and dissociation. These findings provide direct evidence that a higher NPdensity enhances HOR kinetics, supporting the hypothesis that exsolved NPs play a crucial role in perovskiteanode performance. The results emphasize the importance of optimizing exsolution conditions to maximize thecatalytic activity and efficiency of perovskite-based SOFC anodes.