Alternative SOFC Anode Materials with Ion- and Electron-Conducting Backbones for Higher Fuel Utilization

Abstract

Introduction &Solid oxide fuel cells (SOFC) have a great potential to generate electricity with a high efficiency. Currently, Ni-YSZ cermet is widely used as the SOFC anode material. As anode Ni can be oxidized under a high fuel utilization, however, SOFC fuel can not be fully used. In this study, we analyzed alternative anode materials composed of GDC (Ce0.9Gd0.1O2; ionic conductor), LST (Sr0.9La0.1TiO3; electronic conductor), both of which act as stable ion- and electron-conducting frameworks, respectively, and Ni acts only as an electrocatalyst, as described in Fig. 1. Experimental &Electrolyte-supported cells with ScSZ (10 mol % Sc2O3-1 mol % CeO2-89 mol % ZrO2) plate (20 mmφ×&0.2 mmt) were used in this study. Mixture of LST and GDC (1 : 1 ; vol. %) was used for the anode and was sintered at 1300 oC for 3 h. Mixture of (La0.8Sr0.2)0.98MnO3 (LSM) and ScSZ with a weight ratio of 1:1 was used for the cathode. In order to further improve the anodic performance, Ni nanoparticles were impregnated into the porous LST-GDC composite anode. Electrode area was 8×&8 mm2 and Pt mesh was used as the current collector. Cell performance such as I-V characteristics, anodic overvoltage, and anode-side ohmic loss were measured at 800 oCby feeding humidified fuel. The amount of the catalytic Ni loading was optimized through the I-V measurements, FESEM analysis, and Red-Ox cycling tests. Results and discussion &The optimized amount of Ni loading was difficult to be judged only from the I-V measurements and the SEM figures because there were no obvious difference in the anode performance of the cells impregnated more than 0.0833mg-Ni/cm2. Then, Red-Ox cycling tests were conducted according to the procedure shown in Fig. 2, in order to investigate the stable distribution in which Ni catalytic particles are difficult to aggregate. As a result, the best Ni loading in this study was 0.0833mg-Ni/cm2for which anode voltage degradation was only 2% after 50 Red-Ox cycles, whereas that of Ni-ScSZ, conventional Ni-cermet anode was more than 20%. The STEM-EDX micrographs of the optimized anode are shown in Fig. 3, showing that catalytic Ni nanoparticles were supported on the LST-GDC composite frameworks in highly dispersed manner. Anode degradation mechanisms during cycle durability test suggested from these results are shown in Fig. 4. In the conventional Ni-cermet anodes, Ni grains increase in size with Red-Ox cycling and then its electron conducting framework is broken which deteriorates cell performance. On the other hand, in the best impregnated Ni-cermet anodes, Ni nanoparticles loaded on the LST –GDC composite anodes are difficult to aggregate during Red-Ox cycling. Consequently, the stable electrode frameworks exhibit negligible degradation.