Irreversibility Analysis of Solar Ce-based Thermochemical Cycle

Solar thermochemical hydrogen production is an effective way to use solar energy. Solar thermochemical two-step cycles achieve indirect water decomposition through redox reactions of oxygen carriers, and decreases the temperature of direct pyrolysis water and separate hydrogen and oxygen products in different steps, which attract lots of attentions and investigations. At present, the thermodynamic analysis for solar thermochemical cycles, represented by CeO2/CeO2-δ redox pair, still remain the level of energy analysis. The distribution and cause of irreversible loss need to be further explored and studied. It is found by an irreversibility analysis for the typical solar Ce-based thermochemical cycles that the mechanical loss of vacuum pump working at low partial pressure of oxygen is reduced by means of increasing the amount of oxygen carrier based on the non-stoichiometric redox characteristics. The increment of oxygen carrier derived from the increase of the partial pressure of oxygen causes a large amount of heating and cooling irreversible loss during the switch of high-temperature reduction and low-temperature oxidation processes and the radiation loss related to this part of increment of oxygen carrier, and severely decreases the efficiency of solar hydrogen production. Reducing this part of irreversible loss related to partial pressure of oxygen is the key to improve the efficiency of non-stoichiometric solar thermochemical cycles. The research findings provide theoretical foundation for efficient hydrogen production from solar thermochemical cycles. © 2022, Science Press. All right reserved.