The rapid growth of energy demand and carbon emission poses unprecedented challenges to sustainable development and economic expansion worldwide. Development of clean energy has become a common choice worldwide. The promising alternative clean energies include solar, wind, geothermal, biomass and nuclear. And research and development in energy conversion and storage have becoming increasingly attractive. Solid oxide electrolyzer cell (SOEC) is an advanced electrochemical energy conversion device, which can produce hydrogen or synthesis gas by highly efficient electrolysis of H₂O or CO₂+H₂O using a high temperature heat and electrical energy. The high temperature heat and electricity could be supplied simultaneously by the clean primary energy (solar, wind or nuclear energy). Also, SOEC can be operated reversibly in fuel cell mode (Solid oxide fuel cell, SOFC) for electricity production when additional electricity is needed. SOEC is a potential technology for large scale energy conversion and storage application due to the advantages of highly efficient, simple, flexible and environmentally friendly features. In this paper, the principle of SOEC is introduced respectively in detail from the perspective of thermodynamic and kinetic analysis. The current state-of-the art key materials used in solid oxide electrolysis tests are summarized, including anode, cathode, electrolyte materials and so on. The recent development in advanced stack technologies are overviewed worlwide, the main degradation modes and mechanisms of SOEC are pointed out and discussed, and the economic competitiveness of SOEC technology is carefully analyzed. On this basis, the potential application prospect of SOEC in the future are given.

Contents
1 Introduction
2 Principle of SOEC
2.1 Compositon of Electrolysis cells
2.2 Thermodynamics of electrolysis
2.3 Kinetics of electrolysis
3 Key materials
3.1 Anode materials
3.2 Cathode materials
3.3 Electrolyte materials
3.4 Other materials
4 Research statuses of SOEC stacks
5 Degradation mechanisms of SOEC
5.1 Oxygen electrode
5.2 Hydrogen electrode
5.3 Electrolyte
6 Analysis of economic competitiveness
7 Technological prospects