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To avoid the proneness to degradation due to coking in the operation of solid oxide fuel cells (SOFCs) directly running on methane (CH4) fuels, a modified porous anode of the Ni1−XCoX/YSZ (yttria-stabilized zirconia) cermet prepared by an impregnation method is presented. The influence of the Co alloying content on the cermet microstructure, SOFC characteristics, and prolonged cell performance stability has been studied. Co was incorporated into Ni and formed a solid solution of Ni1−XCoX alloy connected with the YSZ as the cermet anode. The porous microstructure of the Ni1−XCoX/YSZ cermet anode formed by sintering exhibited a grain growth with an increase in the Co alloying content. The electrochemical performance of the cells consisting of the Ni1−XCoX/YSZ cermet anode, the YSZ electrolyte, and the LSM (La0.8Sr0.2MnO3) cathode showed an enhancement by the Ni1−XCoX impregnation treatment for the respective supply of H2 and CH4 to the anode. The cell using the Ni0.75Co0.25/YSZ cermet anode (the Ni0.75Co0.25 cell) showed the highest cell performance among the cells tested. In particular, the performance enhancement of this cell was found to be more significant for CH4 than that for H2; a 45% increase in the maximum power density for CH4 and a 17% increase for H2 at 750 °C compared with the performance of the cell using the Ni/YSZ cermet anode. Furthermore, the prolonged cell performance stability with a continuous CH4 supply was found for the Ni0.85Co0.15 and Ni0.75Co0.25 cells at least for 60 h at 750 °C. These enhancement effects were caused by the optimum porous microstructure of the cermet anode with the low anodic polarization resistance.

Carbon deposition on Ni-based anode is well-known as a major barrier for the practical use and commercialization of hydrocarbon-fuelled solid oxide fuel cells (SOFCs). In this work, Co alloying in Ni-YSZ was studied as an alternative anode material for using CH4 as a fuel. The Ni-YSZ and Ni-Co alloyed-YSZ were prepared by the traditional impregnation method without further mixing processes. After sintering and reduction in H2 atmosphere, the introduced Co can completely dissolved into the Ni lattice and changed the morphology with an increase in the Ni-YSZ grain size and showed a better uniform microstructure. The Co alloying also enhanced the electrochemical performance under CH4 fuel by reducing the resistance and anodic overvoltage. Moreover, the Co addition enhanced the stability of the cell with CH4 a constant load current of 80 mA for 60 h. This performance related to the carbon deposition on the anode surface. The Co alloying showed a high efficiency to suppress the carbon deposition and improved the electrochemical performance of an SOFC cell operating under CH4 fuel.

The performance of Ni/SrO-doped CeO2 (SrDC) anode-supported cells, combined with the Sm2O3-doped CeO2 (SDC) electrolyte layer, has been investigated for the direct supply of a dry CH4. The SrO content in the Ce1-xSrxO2-x solid solution affects the porous structure of the starting anode support comprising of the sintered NiO and Ce1-xSrxO2-x grains and denseness of the SDC layer by co-sintering. The cell using the 5 mol% SrO-doped CeO2 shows the highest cell performance without time-dependent degradation even at 750°C. This cell (the 5SrDC cell) also provides better cell performance with decreasing operating temperature than the conventional Ni/YSZ anode-supported cell (the YSZ cell); the maximum power density of the 5SrDC cell is higher than that of the YSZ cell by 73% at 650°C. This enhancement effect is discussed in light of the mixed ionic-electronic conduction of the CeO2-based solid electrolytes. [ABSTRACT FROM AUTHOR]

Although the cermet consisting of nickel and zirconia is useful as the solid oxide fuel cell anode, the conventional cermet consisting of nickel and yttria-stabilized zirconia (Ni/YSZ) is prone to be deactivated for a direct supply of hydrocarbon fuels. This paper describes a method to retard the deactivation of the Ni/YSZ-based cermet anode by being modified with appropriate incorporation of Co as the alloying element into Ni. The single-type anode-supported solid oxide fuel cell (SOFC) consisting of the Ni0.75Co0.25/YSZ cermet anode, YSZ film electrolyte, and La0.8Sr0.2MnO3 cathode exhibited a prolonged stable SOFC performance at 750°C for dry methane (CH4) feeding compared to the one using the Ni/YSZ anode. The microstructural modification of the cermet anode caused a carbon tolerance effect against CH4 accompanied by a low anodic polarization resistance. [ABSTRACT FROM AUTHOR]