Exceptionally High Performance Anode Material Based on Lattice Structure Decorated Double Perovskite Sr₂FeMo_2/3Mg_1/3O_{6− Δ} for Solid Oxide Fuel Cells

A novel double perovskite Sr₂FeMo_2/3Mg_1/3O_{6− δ} is prepared and characterized as an anode material for solid oxide fuel cells (SOFCs). X-ray diffraction refinement reveals that Mg and Mo cations locate separately in two different B sites (B and B′ in A₂BB′O₆) while Fe occupies both B and B′ sites, forming the lattice structure with the form of Sr₂(Mg_1/3Fe_2/3)(Mo_2/3Fe_1/3)O_{6− δ}. The inactive element Mg doping not only endows the material with excellent redox structural stability but also triggers the creation of antisite defects in the crystal lattice, which provide the material with excellent electrochemical activity. The anode performance of Sr₂FeMo_2/3Mg_1/3O_{6− δ} is characterized in an La_0.8Sr_0.2Ga_0.8Mg_0.2O_{3− δ} electrolyte supported cell with La_0.58Sr_0.4Fe_0.8Co_0.2O_{3− δ} cathode. A peak power density of 531, 803, 1038, and 1316 mW cm⁻² at 750, 800, 850, and 900 °C, respectively, is achieved in humidified H₂. The Sr₂FeMo_2/3Mg_1/3O_{6− δ} shows suitable thermal expansion coefficient (16.9(2) × 10⁻⁶ K⁻¹), high electrical conductivity, and good tolerance to carbon deposition and sulfur poisoning. First-principle computations demonstrate that the presence of Fe_BOFe_B′ bonds can promote the easy formation and fast migration of oxygen vacancies in the lattice, which are the key to affecting the anode reaction kinetics. The excellent overall performance of Sr₂FeMo_2/3Mg_1/3O_{6− δ} compound makes it a promising anode material for SOFCs.