Characteristics of La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ-supported micro-tubular solid oxide fuel cells with bi-layer and tri-layer electrolytes

Abstract

In this study, La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM)-supported micro tubular solid oxide fuel cells (T-SOFCs) with two different configurations, one containing an LSGM–Ce_0.6La_0.4O_2−δ (LDC) bi-layer electrolyte (Cell A) and one containing an LDC–LSGM–LDC tri-layer electrolyte (Cell B), were fabricated using extrusion and dip-coating. After optimizing the paste formulation for extrusion, the flexural strength of the dense and uniform LSGM micro-tubes sintered at 1500°C was determined to be approximately 144 MPa. Owing to the insertion of an LDC layer between LSGM electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)–LSGM cathode, the ohmic resistances of Cell B were slightly larger than those of Cell A at the operating temperatures investigated, mainly because of interfacial resistance, but Cell B exhibited slightly lower polarization resistance than Cell A. The maximum power densities (MPDs) of Cell A were 0.25, 0.35, 0.43, and 0.47 W cm⁻² at 650, 700, 750, and 800°C, respectively, which are slightly larger than those of Cell B, i.e., 0.23, 0.33, 0.42, and 0.41 W cm⁻², respectively, owing to the facts that Cell A exhibited a slightly higher open-circuit voltage and a smaller R_t value. Cell A containing the LSGM (288 µm)–LDC (8 µm) bi-layer electrolyte can be operated at approximately 650°C with an MPD value of approximately 0.25 W cm⁻²; however, a similarly structured single cell containing a Zr_0.8Sc_0.2O_2−δ (ScSZ) (210 µm) electrolyte need to be operated at 900°C, and one containing an Ce_0.8Gd_0.2O_2−δ (GDC; 285 µm)–ScSZ (8 µm) bi-layer electrolyte has to be operated at 700°C. Thus, the advantage of using LSGM as an electrolyte for micro T-SOFC single cells is apparent.