Solid oxide fuel cell cathode diffusion polarization: materials and exergy study

Highlights: • The peak exergy efficiency of the SOFC is achieved at the range of 0.35–0.38. • The peak exergy efficiency of the SOFC is achieved at the cathode pore mean radius in the range of 1.5 × 10⁻⁴ to 2 × 10⁻⁴ cm. • Having the cathode material tortuosity in the range of 2.8–3 increase exergy efficiency of the SOFC. • Reducing the operating temperature to between 850 °C and 1000 °C increase the exergy efficiency. The efficiency of the solid oxide fuel cell (SOFC) still can be enhanced by decreasing the cathode diffusion polarization, however to resolve this problem, band gap materials engineering analysis for the SOFC cathode must be well-thought-out. In this research, we investigated theoretically and analytically the effect of several materials constraints and functional conditions on the air electrode diffusion polarization and its influence on exergy efficiency of the fuel cell. The novel model of this paper is the second part of the model created on the SOFC to investigate the polarization on the electrodes and electrolyte. The model is divided into a number of units axially; for each unit, the thermal equations and the continuity equations of the electrochemical reactions are progressively solved with an iterative approach. The partial differential equations for mass and energy transfer through the cathode were spatially discretized using the finite differences method (FDM). The results shows that in order to maintain the peak exergy efficiency of the SOFCs in applied application environments, it is suggested to have the SOFC air cathode porosity between 0.35 and 0.38, the cathode pore mean radius in the range of 0.00015 to 0.0002 cm, the cathode material tortuosity of 2.9, the SOFC functional temperature between 850 °C and 950 °C, the thickness of the air electrode between 0.01 and 0.02 cm, and have the operating pressure in the range of 3 and 5 bar.