Key Role of Interfacial Cobalt Segregation in Stable Low-Resistance Composite Oxygen-Reducing Electrodes

Area of Science:

• Materials Science
• Electrochemistry
• Energy Conversion

Background:

• Efficient and stable oxygen-reducing electrodes are vital for electrochemical cells, particularly solid oxide fuel cells.
• Composite electrodes, combining mixed ionic-electronic conductors (e.g., La_1-xSr_xCo_1-yFe_yO_3-δ) and ionic conductors (e.g., doped CeO₂), show promise but lack consensus on performance factors.
• Inconsistent performance reported across studies necessitates a deeper understanding of composite electrode behavior.

Purpose of the Study:

• To investigate the critical factors influencing the performance of La_0.6Sr_0.4CoO_3-δ-Ce_0.8Sm_0.2O_1.9 (LSC-SDC) composite electrodes.
• To elucidate the role of cobalt oxide segregation and SDC's ionic conductivity in electrode performance.
• To assess the impact of Co₃O₄ addition on LSC-SDC electrode stability and resistance.

Main Methods:

• Application of three-terminal cathodic polarization to dense, nanoscale LSC-SDC model electrodes.
• Analysis of the effects of Co₃O₄ addition on electrode microstructure and phase evolution under cathodic bias.
• Evaluation of interfacial and electrode resistances to determine performance stability.

Main Results:

• Cobalt oxide segregation to electrolyte interfaces and SDC's ionic conducting paths are key to composite electrode performance.
• Addition of Co₃O₄ reduced LSC decomposition, leading to low and stable interfacial and electrode resistances.
• Under cathodic polarization, Co₃O₄ transformed to CoO, indicating suppressed LSC decomposition and maintained cathodic bias throughout the electrode.

Conclusions:

• Cobalt oxide segregation behavior is a critical consideration for understanding and optimizing composite electrode performance.
• Controlling segregation, microstructure, and phase evolution enables the fabrication of stable, low-resistance composite oxygen-reducing electrodes.
• The findings provide a pathway for designing improved electrode materials for electrochemical energy devices.