IT-SOFC supported on Mixed Oxygen Ionic-Electronic Conducting Composites

Thin oxygen-ion-conducting films (5−10 µm) were prepared and characterized on mixed-conducting porous substrates. When this film is made of a pure ionic conductor, such as a gadolinia-doped ceria (Ce 0.8 Gd 0.2 O 1.9 ) electrolyte material, the assembly can be used as a cathode-supported solid oxide fuel cell (SOFC) for operation at intermediate temperatures (500−600 °C). In this case, a porous anode comprising a Ni-CGO cermet or a Pt coating is deposited on top of the highly conductive electrolyte. Another structure with promising applications is created when the supported gastight layer includes a mixed conductor such as ferrite or cobaltite perovskites acting as oxygen-permeable membrane, which can be applied in the combustion of fuel with pure oxygen or in the intensification of other industrial processes currently using aerial catalytic oxidation. The different supported films and multilayer assemblies were characterized by SEM, EDS-WDX, SIMS, helium, and oxygen permeation, showing that gastight thin films can be achieved (values >1 × 10 −6 mbar L s −1 cm −2 ) by inexpensive coating procedures (screen-printing or slip-casting). The electrochemical properties of thin CGO electrolytes were studied by impedance spectroscopy (EIS) and DC voltammetry on fully assembled fuel cells. It is concluded that thin CGO electrolytes under hydrogen atmosphere have enough n-type electronic conductivity to reduce the cell potential by 5−20% from the Nernst potential, which causes the consequent power density decrease. A possible solution to these leakage currents is the use of a thin electron-blocking layer as stabilized zirconia (YSZ or SSZ) deposited on the fuel-exposed CGO electrolyte side. Oxygen permeation of thin LSFC layers was measured using air and helium (sweep) in the range from 700 to 1000 °C. Supported thin films exhibit much better permeation fluxes than bulk thick membranes, especially when oxygen-reduction catalytic porous coatings were applied.