Operando Isotopic Exchange in Solid Oxide Fuel Cells: Oxygen-Transport Dependency on Applied Potential

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Oxygen transport kinetics in oxide solids are crucial for solid oxide fuel cell (SOFC) performance.
• Traditional methods for determining oxygen transport coefficients (e.g., Isotopic Exchange Depth Profiling with SIMS) are ex situ and do not operate under electrical bias.
• In situ or operando techniques for measuring isotopic exchange under electrical bias in SOFCs are underdeveloped.

Purpose of the Study:

• To develop and validate an operando setup for monitoring oxygen isotopic exchange in SOFCs under electrical polarization.
• To investigate the influence of electrical bias on oxygen mobility in a symmetrical platinum/yttria-stabilized zirconia/platinum (Pt/YSZ/Pt) cell.
• To identify the rate-limiting step in the oxygen transport process within the SOFC system.

Main Methods:

• Development of a novel setup enabling operando monitoring of oxygen exchange in SOFC-type cells under polarization.
• Utilized isotopic surface exchange and diffusion measurements under applied electrical potential.
• Performed homomolecular and heterolytic oxygen exchange reactions to analyze oxygen activation and transport steps.

Main Results:

• The developed setup successfully enabled operando monitoring of oxygen exchange under electrical bias.
• Oxygen mobility was found to be dependent on the applied electrical polarization.
• Oxygen ion incorporation into the yttria-stabilized zirconia (YSZ) electrolyte was identified as the rate-determining step.
• A first-order rate constant dependency of oxygen incorporation on the applied potential was established.

Conclusions:

• The operando technique provides a valuable tool for studying oxygen transport mechanisms in SOFCs under realistic operating conditions.
• Electrical polarization significantly influences oxygen mobility, with ion incorporation being the critical step.
• Understanding and optimizing this rate-limiting step is key to enhancing SOFC performance.