Development and Evaluation of 3-Layer Metal Supported Solid Oxide Fuel Cell Short Stack

Abstract

A solid oxide fuel cell (SOFC) is promising technology because of its high electrical efficiency and environmental performance. SOFC can utilize solid ceramic electrolyte, so it can avoid the problems like corrosion, leakage and electrolyte management that often occur in liquid electrolyte. However, these ceramic based SOFC has weakness in external impacts because of its brittleness and relatively low strength. For this problem, metal-supported SOFC has been suggested. Metal supported SOFC refers to SOFC which replace its ceramic support to metal support for enhancing mechanical strength. Metal-support SOFC includes higher mechanical strength, better resistance to vibrates and impacts than conventional SOFC. So, metal-supported SOFC can be applied to movable applications like automobile, train and ship as well as stationary power generation system. In this study, 3-layer metal-supported SOFC short stack was designed and developed for APU (Auxiliary Power Unit) application. The short stack was composed of metal-supported cells, interconnect plates, ceramic sealant, gasket and metal foams. The metal-supported SOFC cell was fabricated by sinter-joining method and dimension of metal-supported SOFC cell was 120 x 80 mm2 and active cathode area was 110 x 70 mm2. For the material of interconnect plates and metal supports, Crofer 22 APU alloy was used which has high resistance to oxidation, low rate of chrome vaporization and good electrical conductivity of its oxide layer. Also, hybrid sealing system of ceramic sealant and sealing gasket were applied for gas tightness. Electrochemical performance of the short stack was evaluated in 800 ℃. The I-V-P characteristics was measured in 1 L/min of hydrogen and 5 L/min of air. Open circuit voltage (OCV) of the short stack was 3.0 V and it showed stable value. The maximum electrical power of the short stack was 23.1 W. In I-V curve, it seems to nearly linear shape which means ohmic resistance governs overpotential of the short stack. This ohmic resistance may originated in current collection from electrodes and it will be further analyzed. Moreover, the short stack was operated for 120 hours in galvanostatic mode with 2.16 A of discharge current. In the beginning, the operation voltage of the short stack was 2 V and there was no rapid initial degradation. Over time, voltage of the short stack was slightly decreased. After 120 hours, voltage of the short stack was 1.81 V and its degradation rate was 9.5 % per 120 hours. This seems to be due to chrome poisoning of cathode and this problem also will be further analyzed. Figure 1