Lithium-doped \({\text{Li}}_{X} {\text{Fe}}_{0.8} {\text{Co}}_{0.05} {\text{AI}}_{0.15} {\text{O}}_{2 - \delta } \,\left( {X = 1.0 - 1.4} \right)\) anode materials were synthesized by the solid-state technique and investigated for intermediate-temperature solid oxide fuel cell (IT-SOFC) applications. X-ray diffraction analysis combined with Rietveld-type profile refinement confirms the formation of dual-phase-stable LxFCA-based oxides. The structural reliability of the oxides is further supported by FTIR and Raman spectroscopy, which reveal characteristic metal–oxygen vibrational modes and the absence of impurity-related features. Lithium incorporation systematically modifies the defect and transport properties. UV–Vis spectroscopy specifies a progressive reduction in the optical band gap, while thermogravimetric analysis confirms enhanced oxygen vacancy stability at higher lithium contents. Electrical conductivity measurements show thermally activated transport behavior with increased conductivity and reduced activation energy for lithium-doped compositions. Electrochemical impedance spectroscopy reveals decreased ohmic and polarization resistances, indicating improved charge transfer kinetics and mass transport. Due to the structural and transport enhancement properties, the \(L_{1.4} {\text{FCA}}\) anode exhibits the best electrochemical performance, with a peak power density (~ 334 mW cm−2) and an open-circuit voltage (1.05 V) at 550 °C. The controlled lithium substitution is an effective strategy for tuning the properties of the structure, defect, and electrochemical performance of FCA-based anodes for IT-SOFC applications.
Graphical abstract
A structure materials design approach for lithium doped oxides LixFe0.8Co0.05Al0.15O2–δ (x = 1.0-1.4) as anodes, reveals a direct systematic relation between crystallographic expansion, electronic structure modulation, and charge-transport efficiency. Rietveld refinement demonstrates that additive lithium incorporation induces a controlled lattice expansion without compromising structural stability, creating a more flexible structure capable of accommodating defects and facilitating charge delocalization. Structural adaptation leads to systematic band gap narrowing, enhanced electronic conductivity, and a manifest reduction in both ohmic and polarization resistances. The resulting synergy between lattice engineering and transport optimization results in substantially improved electrochemical performance, with the lithium-doped Li1.4FCA composition exhibiting superior power output and voltage stability under an intermediate-temperature fuel cell strategy.
