Additive effect of Ce, Mo and K to nickel-cobalt aluminate supported solid oxide fuel cell for direct internal reforming of methane

Abstract

Direct internal reforming of methane (steam/carbon=0.031, 850 °C) is tested using button cells of Ni-YSZ/ YSZ/LSM in which the anode layer is supported either on Ni-YSZ or on Ni-CoAl₂O₄. The Ni-CoAl₂O₄ supported cell shows little degradation with operating time, as a result of higher resistance against carbon deposition, whereas the Ni-YSZ supported cell deactivates quickly and suffers fracture in 50 h. Upon incorporation of additives such as K, Ce, or Mo into the Ni-CoAl₂O₄ support, cells with 0.5 wt% CeO₂ exhibit the best stable performance as a result of reduced coke formation. Cells with 0.5 wt% Mo exhibit the lowest performance. Although no carbon deposit is detected in the cells with K₂CO₃ additives, their performance is worse than that in the CeO₂ case, and, in constant-current mode, there is a sudden voltage drop to zero after a certain period of time; this time becomes shorter with increasing K content. The injection of potassium into the anode side facilitates the generation of OH⁻ and CO ²⁻₃ in the anode and promotes the diffusion of these ions to the cathode. Increased polarization resistance at the cathode and increased electrolyte resistance result in such a sudden failure.