Solid oxide electrolysis cells – current material development and industrial application

Abstract

Solid Oxide Electrolysis Cells (SOECs) have proven to be a highly efficient key technology for producing valuable chemicals and fuels from renewably generated electricity at temperatures between 600 °C and 900 °C, thus providing a carbon-neutral method for energy storage. The successful implementation of this technology on an industrial level in particular requires the long-term stability of all system components with a concurrent overall degradation rate of a maximum of 0.75% kh⁻¹ or even better 0.5% kh⁻¹, corresponding to a performance loss of 20% over approx. five years under constant operating parameters. However, the materials currently used for SOEC systems have been developed and optimized in recent decades for fuel cell operation. The degradation of these Solid Oxide Fuel Cell (SOFC) materials used in SOECs, however, slows down the technology and market ramp-up. Accordingly, a selection and development of materials specifically for use in SOEC operation, must therefore be based not only on the highest performance but also on the lowest achievable degradation rate. In general, the systematic development of new SOEC materials must be driven towards key performance parameters such as mechanical, thermal, and chemical stability as well as an application-oriented assessment (cost effectiveness, simple manufacturing). This review presents the state-of-the-art materials in current industrial use for planar SOECs as well as future challenges regarding materials design and degradation. Recent advances in material compositions are discussed and evaluated in terms of their performance, stability, and potential for industrial implementation. In addition, a materials selection for interconnects, coatings, and sealants is briefly listed to outline current developments in these areas.