An active and stable hydrogen electrode of solid oxide cells with exsolved Fe–Co–Ni nanoparticles from Sr2FeCo0.2Ni0.2Mo0.6O6-δ double-perovskite

Sr₂FeCo_0.2Ni_0.2Mo_0.6O_6-δ (SFCNM) and Sr₂FeNi_0.4Mo_0.6O_6-δ (SFNM) were prepared as the hydrogen electrode materials for solid oxide cells (SOCs) and comparatively investigated by density function theory (DFT) and experiments to demonstrate the benefit of Co addition. The reduced SFCNM (R-SFCNM) and SFNM (R-SFNM) contain exsolved Fe–Co–Ni and Fe–Ni nanoparticles, respectively. DFT indicates that Fe–Co–Ni has optimized combination of the d-band center (descriptor of catalyst activity) and adsorption behavior for H₂O, H₂, H, and OH. The cell with SFCNM hydrogen electrode, La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM) electrolyte, and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) oxygen electrode (Cell-SFCNM) demonstrates a higher performance than that with an SFNM hydrogen electrode (Cell-SFNM) at temperatures between 700 and 850 °C in both solid oxide fuel cell (SOFC, 3% H₂O-97% H₂/air) and solid oxide electrolysis cell (SOEC, 20% H₂O-80% H₂/air) modes. At 850 and 700 °C, the peak power density is 1.23 and 0.48 ​W·cm⁻² in SOFC mode, while the current density is 1.25 and 0.37 ​A·cm⁻² at 1.3 V in SOEC mode, respectively. The performance degradation rates at 750 °C are 0.17 ​mV·h⁻¹ in SOFC and 0.15 ​mV·h⁻¹ in SOEC modes within 150 ​h, which are improved by Co doping.