Fabrication and characterization of all-ceramic solid oxide fuel cells based on composite oxide anode

All-ceramic solid oxide fuel cells (SOFCs), which offer advantages in carbon tolerance, sulfur resistance and redox stability, are fabricated and evaluated. The electrolyte-supported cells are composed of a La _0.75Sr_0.25Cr_0.5Mn_0.5O _3-δ (LSCM)-Ce_0.9Gd_0.1O _1.95-δ (GDC) anode, an Y₂O₃-stabilized ZrO₂ (YSZ) electrolyte, a GDC interdiffusion barrier layer, and a La_0.8Sr_0.2Co_0.2Fe_0.8O _3-δ (LSCF)-GDC cathode. A particle-dispersed glycine-nitrate process is developed to synthesize extremely fine and homogeneous LSCM-GDC ceramic composite powders. The electrochemical performance of the LSCM-GDC anode is comparable to that of conventional Ni-based anodes. The impedance spectra of the all-ceramic SOFCs are successfully interpreted by the independent characterization of the individual electrodes via half-cell measurements. The impedance of the LSCM-GDC anode is dominated by a low-frequency arc originating from the "chemical capacitance", which is associated with the variation of the oxygen nonstoichiometry in the mixed conducting ceramic electrode. In addition, the impedance arc associated with the electrode-gas interaction is observed in the LSCM-GDC anode. The rate-limiting processes for the LSCF-GDC cathode are observed to be solid-state oxygen diffusion and surface chemical exchange. Herein, the reaction mechanisms and rate-limiting processes of the all-ceramic SOFCs are discussed in detail and compared with those of conventional Ni-based SOFCs.