Review of thermodynamic properties of the components in HI decomposition section of the iodine–sulfur process

The iodine–sulfur thermochemical water-splitting process (I–S process) is regarded as one of the most promising high efficient, CO2 free, and large scale hydrogen production methods. The HI concentration subsection of the HI decomposition section (HIx section) is the most energy consuming portion of the whole process. To optimize the I–S process and improve hydrogen production efficiency, it is significant to extensively investigate and utilize the thermodynamic properties of the components in HIx section. This paper summarizes and reviews the thermodynamic properties of the components in HIx section of the I–S process. The phase equilibrium property and the values of thermodynamic functions of the binary mixtures, i.e., I2-H2O, HI-H2O, HI-I2 and the ternary system HI-I2-H2O are summarized and compared. In addition, the tri-iodide complexation equilibrium is demonstrated and several equilibrium constant expressions provided by different literature are compared. Finally, the thermodynamic models for the ternary system are summarized.

► We review the thermodynamic properties of the HI-I2-H2O system.
► Phase equilibrium properties of the HI-I2-H2O system are demonstrated.
► Thermodynamic functions of the HI-I2-H2O system are reviewed and compared.
► Complexation equilibrium properties of tri-iodide, iodine and iodide are discussed.
► Thermodynamic models for the HI-I2-H2O system are introduced.