Transition of Ion Diffusion Mechanism in BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ Electrolyte Under Real Operating Conditions

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Protonic ceramic fuel cells (PCFCs) are advanced power generation devices.
• Understanding ion transport in electrolytes is crucial for optimizing PCFC performance and design.
• The BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ (BZCYYb) electrolyte is a benchmark material for protonic conduction.

Purpose of the Study:

• To elucidate the ion diffusion mechanisms within the BZCYYb electrolyte under various operating conditions.
• To investigate the influence of hydration and temperature on the conductive properties of BZCYYb.
• To identify novel protonation pathways and their implications for PCFC operation.

Main Methods:

• Electrochemical impedance spectroscopy (EIS) to analyze conductivity.
• Single cell testing under varied atmospheres and temperatures.
• H₂O-temperature-programmed desorption coupled with mass spectrometry.
• Time-of-flight secondary ion mass spectrometry (ToF-SIMS) for chemical analysis.
• Theoretical calculations to model ion transport.

Main Results:

• BZCYYb exhibits excellent oxygen-ion conductivity at intermediate temperatures before hydration.
• Upon hydration, BZCYYb becomes a mixed proton and oxygen-ion conductor.
• A new mechanism of protonation via grain boundary hydrogenation was identified under dry hydrogen fuel.
• In situ water generation at the cathode contributes to protonation, reducing the need for humidified fuel.
• Dehydration above 600°C shifts conductivity towards mixed ionic transport.

Conclusions:

• The study provides critical insights into ion diffusion dynamics in protonic perovskites.
• Findings facilitate the rational design and operational optimization of next-generation PCFCs.
• The identified protonation mechanism offers new strategies for efficient PCFC fuel utilization.