Solid Oxide Electrolysis Cell for Hydrogen Generation: General Perspective and Mechanism

Low-temperature electrochemical hydrogen production process, such as proton-exchange membrane electrolyzer and alkaline electrolyzer, uses expensive noble metal catalysts and requires higher electrical energy for water oxidation. A solid oxide electrolysis cell (SOEC) operating at a higher temperature provides a highly energy-efficient and cost-effective route of hydrogen production with comparatively less electricity consumption. Moreover, the use of less expensive ceramic electrolytes and electrodes has added a value to its application. Proton (H+)-conducting solid oxide cell (H-SOEC) provides the scope of dry and pure hydrogen production at reduced temperature (<600 °C). It also provides the scope for compressed hydrogen production via electrochemical compression. SOEC can be operated reversibly in solid oxide fuel cell (SOFC) mode to generate electricity utilizing the produced hydrogen when renewable power sources are unavailable, with only water as the byproduct. In the case of SOEC, there lies the scope for large-scale hydrogen production as the stack size can be scaled up to MW range. Besides generating hydrogen from H2O, SOEC provides the advantage of H2 production from NH3, converting CO2/CO to value-added chemicals and converting CH4 and C2H6 to olefins. This chapter starts with a distinctive comparison of hydrocarbon and hydrogen economies, then proceeds with a thorough review of the mechanism of water electrolysis in both proton- and oxide-conducting electrolysis cells, different electrolytes and electrode materials used, and their operating mechanisms. The chapter also discusses the thermodynamic and electrochemical aspects of electrolysis, current–voltage characteristics, Faradaic efficiency, and hydrogen generation rate of SOEC. There is a detailed coverage on the durability and market competitiveness aspects of SOEC at the end. Learning objectives: