Ni-Substituted Sr₂FeMoO_6−δ as an Electrode Material for Symmetrical and Reversible Solid-Oxide Cells

This work develops a novel perovskite Sr 2 FeNi 0.35 Mo 0.65 O 6−δ (SFN 0.35 M) simultaneously using as a fuel electrode and oxygen electrode in a reversible solid oxide cell (RSOC). SFN 0.35 M shows outstanding electrocatalytic activity for hydrogen oxidation, hydrogen evolution, oxygen reduction, and oxygen evolution. In situ exsolution and dissolution of Fe–Ni alloy nanoparticles in SFN 0.35 M is revealed. In a reducing atmosphere, SFN 0.35 M shows in situ exsolution of Fe–Ni alloy nanoparticles, and then the Fe–Ni alloy is reoxidized into SFN 0.35 M while converting into an oxidizing atmosphere. The polarization resistances of SFN 0.35 M electrode are 0.043 Ω cm 2 in 20% O 2 –N 2 and 0.064 Ω cm 2 in H 2 at 850 °C. Moreover, symmetric fuel cells using the SFN 0.35 M electrode achieves a maximum power density of 0.501 W cm –2 at 850 °C in H 2 fuel, while the symmetric electrolysis cell has an electrolysis current density of 0.794 A cm –2 at 1.29 V in 90% H 2 O–10% H 2 at 850 °C. It is the first time we demonstrate that the cell voltage of symmetrical cell at 0.5 A cm –2 in the fuel cell mode and −0.5 A cm –2 in the electrolysis cell mode can be fully recovered in 10 electrode alternating cycles and therefore demonstrate the possibility that SFN 0.35 M can be used in a fully symmetric RSOC stack with electrode alternating functions.