High-Temperature Protonic Conduction in La₂NiO_{4+ δ}-Based Ruddlesden-Popper Type Oxides: Correlation with...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Oxygen-excess La₂NiO₄₊δ (LNO) exhibits mixed ionic and electronic conductivity, showing promise for protonic ceramic fuel cells.
• Proton incorporation in LNO is facilitated by interstitial oxide ions via hydration, differing from oxygen-deficient oxides.

Purpose of the Study:

• To investigate the effect of substituting Ni with Cu and Co on interstitial oxide ion concentration and proton incorporation in LNO.
• To elucidate the role of interstitial oxide ions in proton transport mechanisms.
• To optimize LNO for enhanced proton conductivity.

Main Methods:

• Chemical substitution (Cu, Co) to tune interstitial oxide ion concentration.
• Theoretical calculations to determine proton localization.
• Hebb-Wagner direct current polarization method with a blocking electrode (La₀.₉₉Ca₀.₀₁NbO₄₋δ) to measure protonic conductivity.

Main Results:

• Cobalt doping increased interstitial oxide ion concentration and proton concentration.
• Theoretical calculations showed protons prefer interstitial sites in Co-doped LNO.
• Copper doping induced a proton trapping effect, reducing mobility.
• Co-doped LNO demonstrated the highest protonic conductivity among the tested samples.

Conclusions:

• Interstitial oxide ions play a crucial role in proton hydration in oxygen-excess LNO.
• Cobalt doping significantly enhances proton conductivity in LNO by increasing interstitial oxide ions.
• Optimized LNO materials hold potential for advanced fuel cell applications.