Formation of atomic fluorine anions in 12CaO·7Al2O3

The storage of atomic fluorine anions (F−) is an important issue in the development of emission materials that have numerous technological applications including catalysis. Using density functional theory simulations, we examine the formation of F− ions from gaseous F2 in the nanoporous complex oxide 12CaO·7Al2O3 (C12A7). Both stoichiometric and electride forms of C12A7 strongly encapsulate fluorine atoms, and the formation of F− ions is confirmed from the charge analysis. There is a significant enhancement in the encapsulation in the electride form of C12A7 due to the presence of electrons in its nanocages. Successive encapsulation of multiple F atoms is also energetically favorable in both forms of C12A7. The formation of molecular fluorine (F2) in the nanocages of both forms is unfavorable due to the strong electronegativity of fluorine.