Hung H. Nguyen

In the context of energy applications for salts and, more specifically, in the case of molten salt reactors, the solvation of corrosion species, the nature and behavior of radiation-produced excess electrons, transient radicals, and molecular gas species all depend on the Lewis acid–base behavior of the constituent salt melt. Speciation of dissolved species and their transport properties are also influenced by the ability of the melt to form networks. This article focuses on the structural properties of melts composed of alkaline earth metal ions coupled with the Cl^– anion, and the quantum mechanical behavior of Cl₂, a typical product of the reaction of radiation-produced chlorine radicals in Cl^–-based molten salts. We explore the effect of M²⁺ Lewis acidity on chlorobasicity, seen in this work as the availability of Cl^– ions to chemically react with Cl₂ to produce Cl₃^–.

Ionic liquids (ILs) used in solar, electrochemical, nuclear, or even space exploration applications will necessarily be exposed to conditions in which electron detachment may occur and transient charge-depleted radical species may form. In a recent article (J. Am. Chem. Soc. 2025, 147, 23395–23398), we studied the different possible kinetic fates of an excess electron in the popular 1-butyl-1-methylpyrrolidinium dicyanamide IL but did not address the nature of electron-deficient transient radical species these leaving electrons produce, the so-called holes. Using pulse radiolysis measurements and first-principles calculations in the bulk and gas phases to interpret these, we show that the most likely hole species in this IL is a dimer radical anion that, somewhat surprisingly, has similar spectral features to the excess electron, including a broad near-infrared absorption band.

Ionic liquids (ILs) for electrochemical, nuclear, and solar energy applications operate under harsh conditions, where electrons and transient radical species can form. This communication discusses why anions such as bis(trifluoromethylsulfonyl)imide (Tf₂N^-) are reduced at the electron-rich electrode whereas in laser photoionization or pulse radiolysis studies, where electrons are ejected from species in the bulk, we often detect long-lived electrons in cavities that interact with IL cations instead. This work argues that bulk excess electrons generated photolytically or radiolytically follow kinetically favored pathways. As such, cavity electrons may not be the most energetically favorable states, but when they form, and they do form, they are kinetically stable. Reduction reactions of anions or electron localization in cavities and subsequent reactions are all expected outcomes. Here we focus on a pyrrolidinium-based IL of the dicyanamide (N(CN)₂^-) anion because of its large electrochemical window and very low viscosity, which are ideal for energy applications.

New and exciting frontiers for the generation of safe and renewable energy have brought attention to molten inorganic salts of fluorides and chlorides. This is because high-temperature molten salts can act both as coolants and liquid fuel in next-generation nuclear reactors. Whereas research from a few decades ago suggests that salts are mostly unreactive to radiation, recent experiments hint at the fact that electrons generated in such extreme environments can react with the melt and form new species including nanoparticles. Our study probes the fate of an excess electron in molten ZnCl2 using first-principles molecular dynamics calculations. We find that on the time scale accessible to our study, an excess electron can be found in one of three states; the lowest-energy state can be characterized as a covalent Zn2Cl5 (center dot 2-) radical ion, the other two states are a solvated Zn center dot+ species (ZnCl3 center dot 2-) and a more delocalized species that still has some ZnCl3 (center dot 2-) character. Since for each of these, the singly occupied molecular orbital (SOMO) where the excess charge resides has a distinct and well-separated energy, the different species can in principle be characterized by their own electronic spectra. The study also sheds light onto what is commonly understood as the spectrum of a transient radical species which can be from the SOMO onto higher energy states or from the melt to pair with the excess electron leaving a hole in the liquid.