Fabrication and Investigation of Anode-supported Intermediate Temperature Solid Oxide Fuel Cells with Composite Ceria-based Electrolyte Films

• Main Authors: Cheng-Hung Chung, 鍾振泓
• Other Authors: 鄭淑芬
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/02103700146146232649

博士 === 國立臺灣大學 === 化學研究所 === 96 === Ce0.8Gd0.2O2-δ (CGO) powder samples were synthesized using citrate sol-gel combustion method, and then the composite electrolyte materials were prepared by a small amount of 1mol% Bi2O3, GeO2, Nb2O5 to CGO. The results show that the densification and conductivity of composite electrolyte were improved. In addition, undergoing 10% H2/N2 for ~ 85h, the conductivity at 700°C in air of the samples could be retained nearly at their starting conductivity. The fabrication of anode-supported intermediate temperature solid oxide fuel cell (IT-SOFC) was carry out by using sandwiched dry-pressed technique with flour layers, because of humid environment in Taiwan, ultrafine CGO powder as electrolyte material. The single cell showed that electrolyte was 16 ± 2 μm in most thin thickness, anode (60wt%-NiO/CGO) and cathode (La0.8Sr0.2Co0.8Fe0.2O3-δ) were 493 ± 7 and 152 ± 4 μm in thickness, respectively. At our best knowledge to build the electrochemical testing device, and the performances of single cell were ~ 450 mW/cm2 (PPD) and ~ 0.79V (OCV), while 100%H2 and air with optimum flow rate of 50 and 150 mL/min at 700°C. On the other hand, under 100%H2 and 100%O2 with optimum flow rate of 50 and 90 mL/min, the the performances were ~ 504 mW/cm2 and ~ 0.82V. The rate-determining step (RDS) was depended on operation temperature: Under 550°C, RDS was oxygen reduction reaction. Above 600°C, RDS was ohmic loss. To exchange of electrolyte material, the addition of 1mol% GeO2 to CGO film was made, under the optimum flow rate through air and 100%O2 in turn, the PPD of single cell were ~ 462 and ~ 521 mW/cm2, respectively, which were improving ~ 12 and ~ 17 mW/cm2, respectively. To exchange of cathode material, the addition of 5.02wt% Pt to LSCF cathode was made, under the optimum flow rate through air and 100%O2 in turn, the PPD of single cell were ~ 526 and ~ 582 mW/cm2, respectively, which were improving ~ 76 and ~ 78 mA/cm2, respectively. To exchange of anode material, the addition of 2.5wt% Mn to Ni/CGO anode was made, under flow rate of 5mL/min through 100%H2 and 100%CH4 at 700°C in turn, the sample displayed about one-third and three-fifth times of the performances of pure Ni/CGO anode, in addition, the performance decreased with long-time. The primary reasons were suggested following: the addition of 1mol% GeO2 to CGO was improving oxide-ion conductivity of electrolyte, thus the influence improved the performance of single cell. However, a small amount of 1mol% Bi2O3 or Nb2O5 to CGO was deteriorating short-circuit short-circuit of electrolyte. For composite Pt/LSCF cathode, the adequate amount of Pt to LSCF was selected due to low oxide-ion conductivity and optimum microstructure surface of self. For composite Mn-Ni/CGO anode, the dense microstructure on surface was observed by the addition of Mn to Ni/CGO , thus the performance of single cell was deteriorating for the direct electrochemical oxidation of methane.