This review summarizes state of the art metal oxide materials used in two-step thermochemical redox cycles for the production of H2 and CO from H2O and CO2 using concentrated solar energy. Advantages and disadvantages of both stoichiometric (e.g. iron oxide based cycles) and nonstoichiometric (e.g. ceria based cycles) materials are discussed in the context of thermodynamics, chemical kinetics, and material stability. Finally, a perspective aimed at future materials development and requirements necessary for advances of process efficiencies is discussed.
