Half-Cell Study of La and Ca Doped Strontium Titanates Anode for Direct Methane Solid Oxide Fuel Cell

Abstract

Solid oxide fuel cell (SOFC) has been providing high conversion efficiency of chemical energy to electricity without any pollution. One of the major advantages of SOFC over other fuel cell is use of direct natural gas at high temperature without any external reformer. Conventional Ni-yttria stabilized zirconia (YSZ) composite anode provides excellent catalytic property, current collection and stability for H2 oxidation but it is not tolerant towards sulphur poisoning and also accelerates coke deposition in presence of hydrocarbon fuels. It necessitates the use of alternate anode for direct hydrocarbon SOFC. In the present work, attempts have been made to apply A-site deficient La and Ca doped SrTiO3 (LSCTA-) as potential anode for direct methane SOFC. Electrolyte supported half-cells with LSCTA- anode backbone have been tested in H2 and humidified CH4 fuel. Low catalytic activity of LSCTA- towards electro oxidation of fuel is significantly improves in presence of metallic catalyst. 6% CeO2 loading in LSCTA- backbone improves the performance of the cell in H2 as well as in humidified CH4 at 800 °C. It has been observed that coke deposition did not degrade the anode active surface even after 6 h of exposure of CH4 at the elevated temperature of 800 °C. 4% Ni infiltration in 6%CeO2-LSCTA- enhances the performance from 131 mW cm-2 to 200 mw cm-2 at 800 °C in H2. In humidified CH4 environment, cell having 4% Ni-6% CeO2-LSCTA- anode shows lesser performance (140 mw cm-2 Power density) due to sluggish methane oxidation reaction but provided enhanced power density (216 mw cm-2) once H2 is again fed after 6 h cell operation in humidified CH4. i-V/ i-P analysis of half-cell shown in fig. 1 explains the performance in H2 as well as in CH4 at 800 °C. Maximum power density of cell is 200 mW cm-2 (554 mA cm-2) at 1 h of operation in H2, which increases up to 216 mW cm-2 (578 mA cm-2) in H2 after 6h of cell operation in humidified CH4. In humidified CH4 exposure, maximum power density of cell is 89 mW cm-2 (285 mA cm-2) at 1 h of operation, which increases up to 140 mW cm-2 (409 mA cm-2) at 6 h of operation. The performance of the cell is reasonably good as results presented here correspond to a cell having thick electrolyte (300 μm). The cells are found to be structurally robust even after 12 h of accelerated testing. LSCTA-is a potential anode backbone material for direct methane SOFC and could be an excellent anode for other hydrocarbons. Key Words: A-site deficient SrTiO3, Direct Methane SOFC, LSCTA- anode, half-cell study. Figure 1