Oxygen isotope exchange in La2NiO(4±δ)

Area of Science:

• Materials Science
• Solid State Chemistry
• Chemical Engineering

Background:

• Oxygen surface exchange and diffusion are critical for mixed ionic-electronic conducting materials used in energy applications.
• Understanding these processes in lanthanum nickelate (La2NiO(4±δ)) is essential for optimizing its performance.
• Previous studies often simplified the complex surface reaction mechanisms.

Purpose of the Study:

• To investigate oxygen surface exchange kinetics and diffusion in La2NiO(4±δ) using a novel modeling approach.
• To determine the rates of elementary stages involved in oxygen incorporation.
• To identify rate-determining steps and analyze diffusion pathways.

Main Methods:

• Isotope exchange method with gas phase equilibration.
• Utilized a static circulation experimental rig.
• Operated within a temperature range of 600–800 °C and oxygen pressure range of 0.13–2.5 kPa.
• Developed a novel model accounting for distributions in dissociative adsorption and incorporation rates.

Main Results:

• Calculated the rates of elementary stages for oxygen surface exchange.
• Identified rate-determining stages for La2NiO(4±δ) polycrystalline specimens.
• Observed significant differences in diffusion activation energies: 1.4 eV (gas phase equilibration) vs. 0.5–0.8 eV (isotope exchange depth profiling).

Conclusions:

• The developed model provides a more comprehensive understanding of oxygen surface exchange kinetics.
• Discrepancies in diffusion activation energies highlight the crucial role of different oxygen diffusion pathways.
• These findings are vital for designing and improving materials for oxygen separation membranes and solid oxide fuel cells.