Reaction process in the Ni-ScSZ anode for hydrocarbon fueled SOFCs

Hydrocarbon fueled cell reactions, which consist of thermal decomposition, reforming, and CO shift reactions, and electrochemical oxidation in the Ni-ScSZ anode of solid oxide fuel cells, were examined by electrochemical measurements and outlet gas analysis for several hydrocarbon fuels (C H4, C3 H8, C8 H18, C12 H26). Examinations on the anode potential and its relation to observed outlet gas compositions have revealed that hydrogen molecules were mainly electrochemically oxidized even for hydrocarbon fuels. The electrode conductivities can be well correlated with the water vapor partial pressure for both hydrogen and hydrocarbons. Water vapor produced as a result of the electrochemical oxidation of hydrogen promotes the hydrogen-producing reactions in the vicinity of the electrochemically active site. A large difference in the thermal decomposition of hydrocarbons appeared in the anode potential and also in the maximum fuel utilization between methane and other hydrocarbons. A simple reaction model has been proposed to interpret consistently the electrode reactions as well as the reforming and the CO shift reactions with a focus on the oxygen atoms on Ni surfaces as a catalyst for both the electrode and the reforming reactions.