Materials for Connecting Solid Oxide Fuel Cells (Overview)

Abstract

Solid oxide fuel cells (SOFCs) are among the most promising energy-generating devices, offering high efficiency, environmental friendliness, and flexibility to use a wide range of fuels. The main components of an SOFC are an electrolyte, an anode, a cathode, and a connector (interconnect). The operating principle of SOFCs is as follows. Oxygen is supplied to the cathode, where it is reduced. Oxygen ions move through a dense ceramic electrolyte (ionic conductor) from the cathode to the anode. Meanwhile, hydrogen is supplied to the anode, where a catalyst (metallic nickel) promotes its dissociation into atoms. When hydrogen is oxidized, it releases electrons into the external electric circuit, forming water in the process. The water formation reaction is exothermic. As a result, a constant electric current flows through the external electric circuit, enabling the direct conversion of chemical energy into electrical energy. The interconnect is a component that connects individual fuel cells into a power system — an SOFC stack. A brief overview of materials for ceramic fuel cell connectors (interconnects) and areas for improving their properties are provided. The classification of ceramic (lanthanum chromite LaCrO₃) and metallic (chromium-based alloys, nickel–chromium alloys, and ferritic stainless steels) interconnect materials is presented. Ceramic interconnects are commonly used for high-temperature SOFCs (~1000°C). The disadvantages of these materials include the difficulty of manufacturing interconnects with complex shapes and their high cost, resulting from the use of rare-earth elements. Among metallic materials, ferritic stainless steels with high chromium content (Crofer 22 APU and Crofer 22) are the most promising in terms of key performance indicators. The main shortcomings of modern chromium-based steel materials for interconnects in SOFC energy systems and the principles for changing the development paradigm for advanced lightweight materials with improved properties are outlined. The replacement of chromium steels with promising titanium-based composites is proposed.