Influence of Lanthanum Doping on Structural and Electrical/Electrochemical Properties of Double Perovskite Sr₂CoMoO₆ as Anode Materials for Intermediate-Temperature Solid Oxide Fuel Cells

Lanthanum (La³⁺)-doped double perovskites Sr₂CoMoO₆ (Sr_2-xLa_xCoMoO₆, 0.00 ≤ x ≤ 0.03) were synthesized via the citrate-nitrate autocombustion route. The Reitveld refinement analysis of X-ray diffraction reveals the tetragonal symmetry as the main phase with space group I4/m and also confirms the presence of some peaks corresponding to extra phase SrMoO₄. The SEM micrograph images reflect that grains are in irregular shape and sizes for all samples. Average grain size gradually decreases with the increase of the SrMoO₄ phase. The X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of mixed valence states of Mo⁵⁺/Mo⁶⁺, Co²⁺/Co³⁺, and O-lattice/O-chemisorbed/O-physisorbed species. Coefficient of thermal expansion (CTE) analysis shows that the particular composition Sr_1.97La_0.03CoMoO₆ has the lowest CTE value among the compositions studied. The electrical conductivity of Sr₂CoMoO₆ is enhanced effectively by doping La at Sr sites. The measured area-specific resistance (ASR) for the composition Sr_1.97La_0.03CoMoO₆ (SLCM03) is found to be appreciably low, ∼0.053 Ohm cm^-2 at 800 °C. The obtained highest electrical conductivity with the lowest activation energy and low ASR value for the composition Sr_1.97La_0.03CoMoO₆ encompasses it as a promising candidate for anode material in the intermediate-temperature solid oxide fuel cell (IT-SOFC) application.