Exergetic Studies of Intermediate-Temperature, Solid Oxide Fuel Cell Electrolytes

The exergetic and thermal efficiency of hybrid systems using various solid oxide fuel cell (SOFC) intermediate-temperature fuel cell electrolytes at various temperatures and electrolyte thicknesses was simulated and evaluated. Electrolytes reported on here include lanthanum strontium gallate magnesite, yttria-stabilized zirconium, and gadolinium-doped ceria oxide (GDC). The Wagner mass transfer model (MTM), which includes solid-state oxygen-ion, hole, and electron conduction, was incorporated into a thermodynamic model for a simple hybrid system. The MTM-projected performance trends for the various electrolytes agreed well with trends previously observed experimentally by the authors for electrolytes alone. The projected exergetic performance with the typical thermodynamic model without the incorporation of the MTM generally gave higher performance over a broader temperature range than expected through experimental trends previously observed. Thus, the projected performance of these very important hybrid systems can be greatly impacted by electrolyte choice and electronic conductivity. GDC was predicted to have a good exergetic efficiency, but only over a very narrow temperature region. A thermodynamically consistent picture of SOFC exergetic performance from the defect chemistry and solid-state electrochemistry to the phenomenological fuel cell and macroscopic thermodynamic performance was established.