Nickel-Induced Lattice Defects Limit Proton Uptake in Barium Zirconate Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-state Chemistry

Background:

• Nickel is crucial for hydrogen electrodes in proton-conducting ceramic electrochemical cells.
• Incorporating nickel into electrolytes like BaZr$_{0.8}$Yb$_{0.2}$O$_{3-δ}$ negatively impacts hydration and proton conductivity.

Purpose of the Study:

• To elucidate the mechanisms by which nickel impedes hydration and proton conductivity in ceramic electrolytes.
• To identify strategies for mitigating nickel's adverse effects through point defect engineering.

Main Methods:

• Atomic-resolution scanning transmission electron microscopy
• Density functional theory simulations
• X-ray total scattering and absorption spectroscopy
• Thermogravimetric analysis

Main Results:

• Nickel forms point defect clusters with Yb acceptors, trapping oxygen vacancies and inhibiting hydration.
• Excess B-site cations from nickel oxide addition create antiphase boundaries (APBs) that deplete bulk acceptors.
• Observed hydration suppression quantitatively aligns with defect reaction models.

Conclusions:

• Nickel's detrimental effects are attributed to two novel mechanisms involving defect clusters and APBs.
• Understanding these mechanisms enables targeted point defect engineering for improved electrolyte performance.
• This work opens new avenues for designing advanced proton-conducting ceramic electrolytes.