Abstract
•Chemical thermodynamics background for isothermal redox vs. non-isothermal.•Discusses importance of redox material kinetics, O2 removal, and heat exchanger effectiveness.•Reviews some design considerations for proposed isothermal reactor types.
Solar thermal splitting of water or carbon dioxide is a promising technology for producing hydrogen or carbon monoxide. In a two-step cycle, a metal oxide is thermally reduced with concentrated solar radiation to release oxygen. The reduced metal oxide is then re-oxidized with steam or carbon dioxide to produce hydrogen or carbon monoxide, or simultaneously with both to produce syngas. The two-step redox cycle can be operated either as a temperature swing where there is a temperature difference between the reduction and oxidation steps or isothermally. This review article discusses various aspects of operating the redox cycle isothermally including redox cycle thermodynamics and overall system efficiency and describes solar reactor concepts based on isothermal operation.