Study of the Change of Electrical Conductivity of Ni-YSZ Cermet Caused by Carbon Formation

The change in electrical conductivity of Ni-YSZ cermet used for the solid oxide fuel cell (SOFC) anode was investigated under methane, ethylene and n-butane feeding. Rectangular-shaped pellets have been prepared and exposed to gaseous mixtures including hydrocarbons and nitrogen with or without steam at 750 °C. In the absence of steam, carbon deposition occurred in the Ni-YSZ pellets and consequently the electrical conductivity decreased exponentially. When steam was fed (steam to carbon ratio = 2) to make carbon formation thermodynamically unfavorable, the electrical conductivity was kept constant, except for supplying butane. The effect of the mole fraction of methane on the change of electrical conductivity was also investigated in the CH4-N2 system. When the molar concentration was increased, the rate of decrease of electrical conductivity was increased. The present study helps to understand the effect of carbon deposition on the electrical conductivity of Ni-YSZ anode.

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Improve electrical conductivity of reduced La 2 Ni 0.9 Fe 0.1 O 4+δ as the anode of a solid oxide fuel cell by carbon deposition

International Journal of Hydrogen Energy ◽

10.1016/j.ijhydene.2015.06.026 ◽

2015 ◽

Vol 40 (31) ◽

pp. 9783-9789 ◽

Cited By ~ 23

Author(s):

Ping Li ◽

Yicheng Zhao ◽

Baolong Yu ◽

Jiang Li ◽

Yongdan Li

Keyword(s):

Electrical Conductivity ◽

Fuel Cell ◽

Solid Oxide Fuel Cell ◽

Carbon Deposition ◽

Solid Oxide ◽

Oxide Fuel

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Modeling of a Solid Oxide Fuel Cell Fueled by Methane: Analysis of Carbon Deposition

Journal of Fuel Cell Science and Technology ◽

10.1115/1.2759504 ◽

2006 ◽

Vol 4 (4) ◽

pp. 425-434 ◽

Cited By ~ 14

Author(s):

J.-M. Klein ◽

Y. Bultel ◽

M. Pons ◽

P. Ozil

Keyword(s):

Fuel Cell ◽

Solid Oxide Fuel Cell ◽

Thermodynamic Equilibrium ◽

Carbon Deposition ◽

Driving Forces ◽

Equilibrium Constants ◽

Solid Oxide ◽

Oxide Fuel ◽

Carbon Formation ◽

Internal Reforming

Natural gas appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems. It mainly consists of methane, which can be converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. However, a major limitation to DIR is carbon formation within the ceramic layers at intermediate temperatures. This paper proposes a model solution using the CFD-ACE software package to simulate the behavior of a tubular SOFC. A detailed thermodynamic analysis is carried out to predict the boundary of carbon formation for SOFCs fueled by methane. Thermodynamic equilibrium calculations that take into account Boudouard and methane cracking reactions allow us to investigate the occurrence of carbon formation. This possibility is discussed from the values of driving forces for carbon deposition defined as α=PCO2∕(KBPCO2) and β=PH22∕(KCPCH4), from the equilibrium constants KB and KC of the Boudouard and cracking reactions, and from the partial pressure Pi of species i. Simulations allow the calculation of the distributions of partial pressures for all the gas species (CH4, H2, CO, CO2, and H2O), current densities, and potentials of both electronic and ionic phases within the anode part (i.e., gas channel and Cermet anode). Finally, a mapping of α and β values enables us to predict the predominant zones where carbon formation is favorable (α or β<1) or unfavorable (α or β>1) according to the calculation based on thermodynamic equilibrium. With regard to the values of these different coefficients, we can say that a carbon formation can be supposed for temperature less than 800°C and for ratios xH2O∕xCH4 smaller than 1.

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