Oxygen exchange material is a kind of oxygen storage material which can release oxygen in a inert atmosphere and restore oxygen in a weak oxidation atmosphere. Thermochemical water splitting (TWS) technology is a promising process for the conversion of solar energy to hydrogen, which strongly replies on the development of the oxygen exchange materials (OEM). In a TWS process, the OEM could release its lattice oxygen via thermal decomposition or by reducing gas heated by solar energy, and then it would be reoxidized with water vapor to produce pure hydrogen. Some suitable OEMs can also be prepared to oxygen transport membranes (OTM), which enable the simultaneous occurence of the oxygen releasing and oxgyen restoring on each side of the materials, producing hydrogen successively. This review mainly introduce the recent developments on the OEMs, including Fe-based oxides, perovskite oxides, Ni-based oxides, Ce-based oxides, OTM. The main challenges in OEM, such as the provement of activity and cyclic stability of Fe-based oxides and perovskite oxides for water splitting, and realization of highly-efficient OTM reactor are discussed. Finally, future development trends in this area are prospected based on our researches.

Contents
1 Introduction
2 Redox oxygen exchange materials (Redox-OEM)
2.1 Thermochemical reduction system
2.2 CH₄ reduction system
2.3 Syngas/CO reduction system
2.4 H₂ reduction system
3 Oxygen Transport Membranes (OTM-OEM)
3.1 CO/H₂ reduction system
3.2 CH₄ reduction system
3.3 Other systems
4 Conclusion and outlook