Abstract: The two-step solar thermochemical cycle based on metal oxides could produce clean solar fuels, and this method is expected to become an effective way to achieve carbon neutrality. The two-step solar thermochemical cycle has the advantages of high theoretical efficiency and no CO2 emissions, and it has attracted much attention. However, the energy conversion efficiency from solar energy to chemical energy is unsatisfactory today. This article starts from the aspects of oxide pairs, reactor design, system optimization, etc., and focuses on the analysis of the factors that affect the conversion efficiency of solar energy to chemical energy. In terms of materials, we focus on summarizing the development history of oxide pairs, and pointing out the importance of DFT and machine learning methods in oxide pairs screening. In the aspect of reactor optimization, the application scope and the existing advantages and disadvantages of particle reactors, foam ceramic/honeycomb structure reactors and membrane reactors are analyzed by combining material characteristics. Better porosity and proper particle radius can speed up the heating rate of the metal oxide base pair, and can effectively reduce heat loss. At the same time, large-scale continuous design can also achieve efficient use of solar energy. In terms of system optimization, the role of new technologies such as digital twins in multi-energy complementary systems is comprehensively analyzed. This article reviews the technology of high-temperature solar thermal chemical cycle to produce solar fuels, and put forward suggestions for future in this field.

Key words: solar energy, thermochemistry, oxide pairs, reactor, system