Deciphering Ni Content-Induced Microstructural Evolution in Ni-YSZ Cermets for Direct Ammonia SOFC Performance

Area of Science:

• Materials Science
• Electrochemistry
• Energy Conversion

Background:

• Solid oxide fuel cells (SOFCs) are promising energy conversion devices.
• Direct ammonia SOFCs (DA-SOFCs) offer an alternative fuel pathway.
• Anode material composition significantly impacts SOFC performance.

Purpose of the Study:

• To investigate the effect of varying nickel (Ni) content in Ni-YSZ anodes on DA-SOFC performance.
• To correlate microstructural characteristics with electrochemical measurements.
• To understand the role of transport properties in anode performance.

Main Methods:

• Fabrication of Ni-YSZ anodes with different NiO/YSZ weight ratios (50:50, 60:40, 65:35).
• Electrochemical measurements including power density and polarization resistance.
• Three-dimensional (3D) microstructural characterization using X-ray micro-computed tomography (micro-CT).
• Quantification of microstructural parameters like percolation, tortuosity, and TPB density.

Main Results:

• Peak power density increased from 122 to 383.9 mW/cm² with rising Ni content (50:50 to 65:35) at 800 °C.
• Polarization resistance, especially charge transfer resistance (R_H), decreased with higher Ni loading.
• Microstructural analysis showed high Ni and YSZ network connectivity (>98.7% percolation).
• No direct correlation was found between total TPB density and polarization resistance.

Conclusions:

• Higher Ni content enhances DA-SOFC performance by improving charge transfer and reducing polarization resistance.
• Microstructural descriptors like tortuosity and percolation are critical for understanding performance limitations.
• The NiO/YSZ (65:35) anode demonstrated good stability over 96 hours with minimal degradation.