Molybdenum Dioxide (MoO2)-Based Anode Fabrication and Its Performance Analysis for SOFC Applications

Molybdenum Dioxide (MoO₂)-Based Anode Fabrication and Its Performance Analysis for SOFC Applications

 

Byeong Wan Kwon^a, Oscar Marin-Flores^a, Shouzhen Hu^a, M. Grant Norton^b, Su Ha^a

 

^a The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164

^bSchool of Mechanical and Materials Engineering, Washington State University Pullman, WA, 99164-2920

Solid oxide fuel cells (SOFCs) are a promising fuel flexible technology for clean and efficient conversion of chemical energy into electrical energy. In SOFCs using hydrocarbons as fuel, hydrocarbons are oxidized on the surface of the Ni-based anode through a pathway that produces carbon deposits known as coking. These carbon deposits deactivate the anode and lead to a poor long-term stability of SOFC. Therefore, a new anode material is required for direct liquid SOFCs having a good coking resistance for a long-term stability.

Our group conducted the fabrication and performance of a porous molybdenum dioxide (MoO₂)-based anode for direct utilization of liquid fuel SOFCs instead of Ni-based anode, which can directly convert liquid fuels into electrical energy without external fuel processors. The MoO₂-based anode was manufactured onto yttria-stabilized zirconia (YSZ) electrolyte with Sr-doped LaMnO₃ (LSM) cathode via combined electrostatic spray deposition (ESD) and direct painting methods. The cell performance was measured by directly feeding n-dodecane, which is a model compound of jet A fuel, to the MoO₂-based anode at 750^oC. The stabilized power densities from our MoO₂-based SOFC were 2000 mW/cm² at 0.6V using n-dodecane as fuels. To test the long-term stability of MoO₂-based SOFC against coking, n-dodecane was continuously fed into the cell for 24 h at its open cell potential of ~0.86V. During this long-term testing, voltage-current density plots were periodically obtained and they showed no significant changes over 24 hr. The X-ray diffraction patterns obtained from the spent MoO₂-based anode after 24 hr of operation indicated that the bulk structure of the MoO₂-based anode exhibit no phase transition. Based on our visual observations, there was no coking. Therefore, the catalytic activity toward the electrochemical oxidation of fuel remains stable even after 24hr operation. On the other hand, SOFCs with conventional nickel (Ni)-based anodes under the same operating conditions showed a significant amount of coke formation on the Ni surface, which led to a rapid drop in cell performance. Hence, the present work demonstrates that MoO₂-based anodes exhibit an outstanding tolerance to coke formation and the power density of the MoO₂ anode is much higher than that obtained with the Ni based anode.

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