A multi-physics based transient, continuum model of a solid oxide half-cell comprising of a porous LSM-YSZ composite cathode sintered to a dense YSZ electrolyte was developed to investigate the oxygen reduction reaction kinetics. The model coupled species, electron and ion transport through the porous cathode to surface and electro-chemistry. The electrochemical reduction of O2was modeled using three candidate elementary kinetic mechanisms. Each mechanism included parallel surface and bulk pathways for O2reduction and was driven by three different electric phase potentials. The mechanisms were compared against three sets of electrochemical impedance spectra and polarization curves measured by Barbucci et al. (2009), Cronin et al. (2012) and Nielsen and Hjelm (2014) over a wide range of operating temperatures (873–1173 K), inlet O2concentrations (5–100%) and overpotentials (−1 V to +1 V). Two of the three mechanisms were able to quantitatively reproduce the three sets of experiments by only tweaking the microstructural parameters for each individual set. Yet on analyzing their kinetic and thermodynamic parameters, the mechanism postulating the chemisorption of gas-phase O2on LSM to form the superoxo-like adsorbate O2 -was determined to be the most realistic. A model-based sensitivity analysis revealed that ionic transport in the YSZ phase, O2dissociation in conjunction with surface to bulk charge transfer in the LSM phase and charge transfer at the three phase boundary were the rate limiting steps throughout the operating space. Additionally, the bulk pathway was found to be insignificant.
- Continuum multi-physics model
- Elementary kinetics
- LSM-YSZ composite
- Oxygen reduction reaction (ORR)
- Reaction mechanism
- Solid Oxide Fuel Cell (SOFC)