All porous SOFC: a bridge of technology between dual and single chamber
Résumé
Single Chamber SOFC (SC-SOFC) has demonstrated high open circuit voltage (OCV) and power density from a methane and air mixture. However, this technology is strongly limited in practice because of flammability and coking issues [1]. Here, a novel concept, an all porous SOFC (AP-SOFC) that employs a dual-chamber SOFC (DC-SOFC) technology with a porous electrolyte is reported. In AP-SOFC, the electrolyte is porous allowing a controlled distribution of gaseous O2 at the anode side. The oxidative reforming of hydrocarbon streams can operate similarly to SC-SOFC but with a safer and well controllable process. In this technology, air and methane are separated by a porous Gd0.1Ce0.9O1.9 (CGO) membrane which controls the traffic of the reactants. This concept of feeding O2 through a porous membrane is known as oxygen distributor technology for a catalytic membrane reactor (CMR). The oxygen partial pressure in the catalytic chamber can be controlled by appling a transmembrane pr essure (?P) between the two compartments [2]. Like this, it is possible to overcome inflammability issues, while providing a smoother temperature profile along the catalytic layer due to the oxygen distribution control [3]. The AP-SOFC technology consequently enables separate fuel-O2 feeding and homogeneous O2 distribution at the anode layer, thereby overcoming the inflammability issues encountered with SC-SOFCs. An electrolyte supported AP-SOFC cell with composition of Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF) cathode/porous CGO electrolyte/Ni-CGO anode was studied. The CH4/O2 mixture (Rmix) at the anode side can be controlled by applying a ?P. At ?P=10 mbar, the OCV achieves ~0.92 V at 625 oC, which is comparable to the value of the cell with dense CGO electrolyte [2,3], and the relative high OCV are also obtained at higher temperature (~0.80 V at 750 oC). The peak power densities of the cell is 21.4 mW cm-2 at 650 oC. The CGO shows relatively high conductivity, and the main resistance of cell is ohmic resistance due to the large thickness. Moreover, the cell can operate for 2000 h without coking. This AP-SOFC is an advantageous technology since the CH4/O2 ratio can be controlled at the cathode side to produce heat by combustion. Keywords: Fuel Cells, Porous electrolyte, Methane fueling. REFERENCES 1.T. W. Napporn, X. Jacques-Bedard, F. Morin, M. Meunier, J. Electrochem. Soc. 2004, 151, A2088-A2094. 2.S. Zha, A. Moore, H. Abernathy, M. Liu, J. Electrochem. Soc. 2004, 151, A1128-A1133. 3.S. Zha, W. Rauch, M. Liu, Solid State Ionics 2004, 166, 241-250.