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.