(74b) Thermodynamic Modelling of Br2-HBr-H2O Ternary System with Enrtl Model

The storage of energy has always been researchers’ concern for decades. As an improvement of fuel cells, the technique of redox flow cells provides us a great balance between energy density and electric-to-electric efficiency. The H₂-Br₂ flow cell system has the advantages in reaction kinetics, power density, energy storage capacity, simplicity, and low cost on materials. In the system, there are molecular components including H₂, Br₂, HBr, H₂O, and ionic components such as H₃O⁺, Br^-, even H₅O₂+. Proper thermodynamic modelling of the complex electrolyte solution is of great importance for further development of the H₂-Br₂ battery system. Wozny looked into phase equilibria of HBr/H₂O system, and a correlation for only pressure was put forward in 1981. Applying electrolyte non-random two liquid model, this work investigates the adjustable pair parameters between molecular-molecular components, molecular-ionic components, and ionic-ionic components. Experimental data of phase equilibria, solubility, and molar enthalpy are used to regress these parameters for both HBr-H₂O binary system and Br₂-HBr-H₂O ternary system. It turns out that ENRTL model works in excellent precision for this system. The redox potential of flows in the cell system can also be evaluated with this model.