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

摘要

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_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) (LSCM)-Ce_(0.9)Gd_(0.1)O_(1.95-δ) (GDC) anode, an Y_2O_3-stabilized ZrO_2 (YSZ) electrolyte, a GDC interdiffusion barrier layer, and a La_(0.8)Sr_(0.2)Co_(0.2)Fe_(0.8)O_(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 non-stoichiometry 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.