Effects of Manganese Oxide Addition on Coking Behavior of Ni/YSZ Anodes for SOFCs

Abstract

Solid oxide fuel cells with Ni-MnO/yttria-stabilized-zirconia (YSZ) tricomposite anode supports were fabricated with different MnO concentrations, and the coking tolerances and catalytic activities were investigated in wet CH4 atmosphere. Ni-0.9(MnO)(0.1)/YSZ (10MnO) anode support cell exhibited a maximum power density of 210, 354, 505, and 620 mWcm(-2) at 700, 750, 800, and 850 degrees C, respectively, in H-2. Moreover, a maximum power density in wet CH4 reaches 504 mWcm(-2) at 800 degrees C; while the Ni/YSZ cell showed poorer performances. The coking tolerance improved with an increase in their MnO content, and the 10MnO anode showed the highest tolerance. 10MnO exhibited stable performance for more than 40 h in wet CH4 without undergoing deactivation. Furthermore, it showed negligible coke formation of 0.0045 g of coke per catalyst, during testing under steam reforming-like conditions at a steam-to-carbon (S/C) ratio of 1. Outlet gas chromatography analysis indicated that MnO suppresses CH4 cracking, while only minimally lowering the catalytic activity of steam reforming. Thus, it can be inferred that MnO promotes the adsorption of steam and oxygen on the reaction sites, owing to its high basicity and oxygen storage capacity. The increase in the local S/C and oxygen-to-carbon ratios suppresses CH4 cracking and promotes coke gasification.