Processing and properties of the ceramic conductive multilayer device solid oxide fuel cell (SOFC)

Abstract

Solid oxide fuel cell (SOFC) systems are worldwide under development in the 1–1000 kW range where shifts from laboratory testing to trials for market penetration become visible. Materials systems are available allowing the processing of multilayer devices mainly out of conductive ceramic materials to fulfill the demands of a fuel cell system with sufficient power density. A main drawback for real market introduction and maturity still is high cost, related to materials as well as processing. Alternative cheaper raw materials, as well as the replacement of expensive and complicated processing steps by cheaper and simpler techniques are being considered. In addition to that the use of new materials with enhanced electronic, ionic and catalytic activities are looked for to show the way to increased power densities, as enlarging power densities means material saving and cost reduction too. The multilayer SOFC device consists of: • a porous, gas permeable, electronic conductive substrate carrier (either acting as anode or cathode); • an anode or cathode functional layer being porous with high specific surface area (three phase boundary contact); • a gas tight ion conducting (negligible electronic conduction) electrolyte; • a cathode or anode functional layer with a porous high specific surface area (three phase boundary contact); • a porous cathode or anode for gas penetration; • contact layers making the electronic joints between cells. The overall processing of this system has to be made as simple as possible (cost effective), i.e. using as few and as cheap as possible processing methods to fulfill the property demands of the single layers and the multilayer device. The set of multilayers used today has to be reconsidered looking for superior properties like higher ionic conductivity (electrolytes other than YSZ), increased oxygen exchange activity (other perovskites than LSM (La 0.65Sr 0.3MnO 3)), new redox stable and catalytic active anode materials (oxides instead of Ni in Ni/YSZ cermet) as well as new contact layers with improved long-term resistance stability. The state-of-the-art fuel cell is described, processing and properties are given and alternatives for materials and processes will be discussed.