Water vapor electrolysis at high temperature: systems considerations and benefits

Abstract The energy intensiveness of conventional liquid water electrolysis has inhibited the universal acceptance of this established technology as a resource conversion, storage and transport option. New developments in recent years have focused on the goal of reducing electric energy requirements as well as overall system capital cost. Major gains are envisioned in meeting these goals if water vapor electrolysis were conducted at elevated temperatures. The fundamental thermodynamics of a high temperature electrolysis process operating at ∼1000°C are presented. Further, process considerations are examined in terms of engineering requirements which indicate the tradeoff between thermal efficiencies and cost. These gains in efficiency can be of the order of 40–50% over the energy efficiencies attained via conventional liquid water electrolysis. Process tradeoffs are discussed in terms of overall thermal efficiencies, voltage/thermal requirements, steam conversions and heat recovery. These analyses discuss the possible tradeoffs between plant complexity and voltage efficiency and show the incentive for continued research and development support.