A NOVEL NICKEL MOLYBDENUM-CERIA-ZIRCONIA ANODE MATERIAL FOR INTERNAL REFORMING SOLID OXIDE FUEL CELLS

Xiaoxue Hou

This research examines two important aspects of an innovative material, NiMo-ceria-zirconia oxide (NiMo-CZ), as a promising anode to suppress carbon deposition when directly utilizing liquid hydrocarbon fuels: the heterogeneous catalytic activity and electrochemical activity. The NiMo-CZ was first applied as a micro-reforming layer for solid oxide fuel cells running on isooctane/air mixtures. The layer was on top of the conventional anode-supported single cell with a Ni-yttria-stabilized zirconia (YSZ) anode, YSZ/Ce0.8Sm0.2O1.9 bi-layer electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode. The novel catalyst layer effectively enhances the electrochemical oxidation of complex hydrocarbons at the anode. The single cell exhibits a low polarization resistance of 1.36 Ω cm2 and a high maximum power density of 405 mW/cm2 in isooctane/air operation. The cell voltage degrades at a low rate of 3.0 mV/h during a 12 h stability test. This excellent electrochemical performance suggests a high catalytic activity of NiMo-CZ for reforming isooctane and effective suppression of carbon deposition compared to the conventional Ni/YSZ-based anode single cell under direct-fed liquid fuel. The electrochemical oxidation activity and performance stability were also evaluated for NiMo-CZ as sole anode material with Mo contents of 0, 3, and 5 at. %, scandia-doped zirconia as electrolyte, and LSCF as cathode. The initial activity of the anode increases with Mo content. The initial maximum power density of the NiMo-CZ anode significantly increases from 80 to 240 mW/cm2 as the Mo content increases to 5.0%. Replacing YSZ with CZ also stabilizes the cell voltage with a slow degradation rate of 5.7 mV/h for 20 h. This improved stability is attributed to effective carbon removal by lattice oxidation, facilitated by the high oxygen storage capacity of CZ. More importantly, NiMo-CZ (5% Mo) anode single cells show improved performance stability. The degradation rate reduces from 5.7 to 2 mV/h for 24 h. Therefore, both CZ and Mo in a NiMo CZ (5% Mo) anode effectively mitigate carbon deposition and significantly improve the long-term stability compared to a conventional Ni/YSZ anode. The enhanced electrochemical activity and stability demonstrates that NiMo-CZ is a promising candidate anode material for solid oxide fuel cells running under direct isooctane feed.

A NOVEL NICKEL MOLYBDENUM-CERIA-ZIRCONIA ANODE MATERIAL FOR INTERNAL REFORMING SOLID OXIDE FUEL CELLS

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