A detection method for HIx composition in thermochemical water splitting iodine–sulfur cycle

For the HIx section of iodine–sulfur cycle, the sampling and chemical analysis of HI–H2O–I2 solution (HIx) are very difficult, because of the heavy corrodibility and volatility. In this work, density and electro-electrodialysis (EED) cell voltage were selected as two substitute variables to determine the complete composition of HIx, since HIx is considered as a system with 2 degrees of freedom at given temperature and pressure, according to Gibbs phase rule. Densities and EED voltages of a series of prepared HIx solutions were measured at 1 atm and 80 °C. Then multiple regressions were carried out to obtain equations describing HIx's density–composition relationship and EED voltage–composition relationship. As verified, using the consociation equation set consisting of above 2 equations, concentration of HI and I2 of a certain HIx could be worked out by inputting the solution's density and EED voltage, suggesting this newly developed estimation technique could give HIx's composition information by density test and voltage measurement, instead of traditional titrations.