Electrode Performance in Reversible Solid Oxide Fuel Cells

The performance of several negative (fuel) and positive (air) electrode compositions for use in reversible solid oxide fuel cells capable of operating both as a fuel cell and as an electrolyzer was investigated in half-cell and full-cell tests. Negative electrode compositions studied were a nickel/zirconia cermet and lanthanum-substituted strontium titanate/ceria composite, whereas positive electrode compositions examined included mixed ion- and electron-conducting lanthanum strontium ferrite (LSF), lanthanum strontium copper ferrite , lanthanum strontium cobalt ferrite , and lanthanum strontium manganite (LSM). While titanate/ceria and electrodes performed similarly in the fuel cell mode in half-cell tests, losses associated with electrolysis were lower for the titanate/ceria electrode. Positive electrodes gave generally higher losses in the electrolysis mode when compared to the fuel cell mode. This behavior was most apparent for mixed-conducting and electrodes, and discernible but smaller for LSM; observations were consistent with expected trends in the interfacial oxygen vacancy concentration under anodic and cathodic polarization. Full-cell tests conducted for cells with a thin electrolyte ( YSZ) similarly showed higher polarization losses in the electrolysis than fuel cell direction.