In-situ exsolution of nanoparticles from Ni substituted Sr2Fe1.5Mo0.5O6 perovskite oxides with different Ni doping contents

Perovskite oxide molybdenum doped strontium ferrite, Sr2Fe1.5Mo0.5O6-delta (SFM), is a promising alternative hydrogen electrode material for solid oxide cells (SOCs) because of its robust stability, but usually suffers from insufficient electrochemical performance. In this work, the easily reducible and catalytically active nickel ion (Ni2+) has been substituted on the B-sites of perovskite oxide SFM in the oxidizing atmosphere to form Sr2Fe1.5-xNixMo0.5O6-delta (SFMNix, x = 0.1, 0.2, and 0.3), and then partially in-situ exsolved out of the parent matrix lattices as active nano-catalysts in the reducing atmosphere to fabricate Fe-Ni alloy nanoparticles decorated SFMNix (Fe-Ni@SFMNix) materials. It is demonstrated that the electrode electrochemical performance could be effectively enhanced by tuning the Ni doping content in the parent oxide. Sr2Fe1.3Ni0.2Mo0.5O6-delta (SFMNi0.2) electrode with the Ni doping content of 0.2 exhibits the excellent electrochemical performance with a relatively low electrode polarization resistance of 0.82 Omega cm(2) in a symmetrical cell at 800 degrees C in 97%H-2 -3%H2O atmosphere, which is ascribed to the maximum exsolved Fe-Ni alloy nanocatalysts from the parent oxide SFMNi0.2. In addition, the electrode reaction process with a high resolution based on the electrochemical impedance spectra has been systematically analyzed by using the distribution of relaxation times (DRT) technique. It is demonstrated by the DRT analysis results that the low-frequency electrode reaction process associated with the hydrogen adsorption, dissociation and ionization process in the frequency range of 1-10 Hz is identified as the rate-limiting step during the operation, meanwhile, this sub-step could be effectively accelerated by varying the Ni doping content with an optimal Ni doping content of 0.2. These results demonstrate that the variation of doping content in the parent perovskite oxide is an effective strategy to manipulate the electrode electrochemical performance, and exsolved Fe-Ni alloy nanoparticles decorated perovskite oxide SFMNi0.2 is a promising hydrogen electrode candidate for SOCs application. Our findings will guide the development of other ceramic oxides electrodes with effectively enhanced electrochemical performance for energy conversion and storage applications. (C) 2020 Elsevier Ltd. All rights reserved.