Exergetic Studies of Intermediate-Temperature, Mixed Ionic-Electronic Conducting Solid Oxide Fuel Cell Electrolytes Using the Wagner Mass Transfer Model

The exergetic and thermal efficiency of various SOFC mixed ionic-electronic conducting (MIEC) intermediate fuel cell electrolytes at various temperatures and electrolyte thicknesses was evaluated. Electrolytes reported on here include: LSGM, YSZ, and GDC (gadolinium doped ceria oxide). Here, results for the hydrogen oxidation reaction are reported. GDC was shown to have a good exergetic efficiency, but only over a very narrow temperature region. The Wagner mass transfer model (MTM) was used to incorporate solid state oxygen ion, hole, and electron conduction effects into a thermodynamic model. The MALT2 data base was used to provide thermodynamic data over the temperatures and compositions of interest. The MTM predicted performance agreed well with the experimental performance. The predicted exergetic performance with the thermodynamic model without the incorporation of the MTM gave higher than experimentally observed results at the higher temperatures for various fuel anodic reactions. 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.