Effect of Gallium Doping on the Oxygen Exchange Kinetics in La2SrFe2O7−δ Ruddlesden–Popper Phases

Abstract

This study investigates the oxygen exchange kinetics between O2 and Ga-doped La2SrFe2O7−δ, focusing on the role of gallium substitution in modifying the surface exchange properties of materials. Two compositions, undoped La2SrFe2O7−δ and Ga-doped La2SrFe1.8Ga0.2O7−δ, were synthesised via conventional solid-state reaction. The phase composition and microstructure of the resulting powders were analysed using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, and laser scattering techniques. Oxygen surface exchange kinetics between the oxides and O2 was studied using the 18O/16O isotope exchange pulsed method across a temperature range of 400–900 °C under a He/16O2 gas carrier mixture (19 vol. % O2). The results reveal that both Ga doping and temperature significantly influence the exchange mechanism and rate-determining step, demonstrating tunable catalytic activity in oxygen reduction reactions relevant to solid oxide fuel cell (SOFC) cathodes.