The Impact of Hydrogen Valence on Its Bonding and Transport in Molten Fluoride Salts
Interest in molten salts has increased significantly over the last decade due to their potential application in various clean-energy technologies including hydrogen generation, solar heat storage, and advanced nuclear power plants. In the development of new molten salt-based fission and fusion systems, controlling hydrogen poses a critical challenge due to its ability to corrode structural materials as 3H+, and its potential to cause significant radioactive release as diffusive 3H0. Yet, the chemistry and transport behavior of the hydrogen species remain poorly understood despite several decades of research. Using ab initio molecular dynamics, we present a coupled examination of hydrogen valence, speciation and transport in the prototypical salts 66.6%LiF-33.3¾F2 (Flibe) and 46.5%LiF-11.5%NaF-42%KF (Flinak). We discovered significant differences between 3H0 and 3H+transport behaviors. 3H+ diffuses 2-4 times slower than 3H0, which can be ascribed to hydrogen bonding and complexation in solution. This work helps explain varying experimental results and provides useful species transport data for designing hydrogen control systems for molten salts.