Solid oxide fuel cells working in a mixed gas atmosphere (fuel and oxidant), the so-called single chamber SOFCs (SC-SOFCs), have been increasingly studied in the past few years. The absence of sealing between the two compartments provides an easier operation than a classical ―two-chambers" SOFC. Operating principle of SC-SOFCs lies on a difference in catalytic activities of both electrodes, which requires improved selectivity of anode and cathode materials to fuel oxidation and oxygen reduction, respectively. Hydrogen-air mixtures are not commonly used under single chamber conditions because of their high reactivity and risk of explosion. Therefore, hydrocarbons are preferentially used as fuel. In this study, SOFCs in a single chamber configuration are investigated as devices for electricity production through gas recycling from an engine exit. Cells would be embedded at the exit of the engine and convert hydrocarbons unburned by combustion into electricity. This forward-looking energy recovery system could be applicable to automotive vehicles as well as to plants. Hibino et al. in 2008 [1-2] demonstrated the feasibility of such a device with stack of 12 SC-SOFCs incorporated at the exit of a scooter engine. However power output was not as high as expected. Optimization of the system including architecture, gas mixture and materials modification may lead to enhanced performances. Our project is focused on anode-supported cells working in a mixture of hydrocarbons (propane and propene), oxygen, carbon monoxide, carbon dioxide, hydrogen and water corresponding to the composition of exhaust gas after the first oxidation catalyst. GDC (Ce0.9Gd0.1O1.95) was chosen as electrolyte because of its high ionic conductivity at temperatures corresponding to the ones of exhaust gases. Concerning cathode, a screening of four materials has been made, some well-known materials through literature [3-4] and leading to highest performances such as LSCF(La_(0,6)Sr_(0.4)Co_(0,2)Fe_(0,8)O_(3-δ ), SSC(Sm_(0.5)Sr_(0.5)CoO3) and BSCF(Ba_(0,5)Sr_(0.5)Co_(0,8)Fe_(0,2)O_(3-δ) ), and one only investigated in ―two-chambers" SOFCs: Pr2NiO_(4+δ) (PNO) [5]. A preliminary study concerning cathode materials has been conducted. Stability tests during five hours and catalytic activity studies in the gas mixture were performed on the raw materials and allowed to make a first choice among cathodes. Two ratios hydrocarbons/oxygen (R) were used for materials testing considering their stability at high temperature: R=0.21 and R=0.44. LSCF and Pr2NiO_(4+δ) were proven to be the most stable cathode materials and LSCF demonstrated a lower catalytic activity towards hydrocarbon partial oxidation than Pr2NiO_(4+δ )especially for a R=0.44 ratio. LSCF can thus be considered as a better cathode material than Pr2NiO_(4+δ.)
展开▼
