Study of the Electron Transfer in Titanium Containing Melts by Electrochemical and Quantum-Chemical Methods

Abstract

The electron transfer mechanism in a titanium containing system was investigated by electrochemical and quantum-chemical methods. The kinetics of charge transfer for the Ti(IV)/Ti(III) redox couple in the (NaCl–KCl)equimol–NaF (10 wt%)-K2TiF6 melt with addition of Ca2+ cations was studied by cyclic voltammetry. The standard rate constants of charge transfer (k s ) were calculated by Nicholson’s method. The increase values of the k s reaching the maximum at mole ratio Ca2+/Ti(IV) equals 1:1 was found. Values of activation energy for system with Ca2+ cations are considerably less than activation energies of the system without Ca2+ cations. The quantum-chemical calculations were performed using the Firefly quantum-chemical package by methods of the density functional theory. Structures with a high probability of the electron transfer from the cathode to the titanium complex were found. Using the Frontier molecular orbital method made it possible with a small amount of computer time to determine the structure of the transition state of the TiF6 2− complex. The calculated activation energy of the electron transfer was in a good agreement with experimentally determined value.

(Digital Presentation) Study of the Intervalence Charge Transfer in a 18NaCl+Na3SmF6 Model System By Quantum Chemical Methods

“…The probability of electron transfer from the electrode surface to the model system under study is determined primarily by the characteristics of the lower unoccupied molecular orbital (LUMO) and closely adjacent unoccupied molecular orbital (UMO) (3,41). The LUMO wave function (and the closely UMO) must be delocalized between boundary cations and the samarium complex.…”

“…Because we were interested the state of the complex SmF 6 3near the cathode surface, on one side of the model system, a flat boundary layer consisting of 10-16 chlorine and sodium ions was formed (3,27,41,42). All such systems were applied an electric field of 10 9 V/m, simulating the field of the cathode (43).…”

“…1 shows the structure of LUMO (a) and LUMO +1 (b) in the initial state of the system 18NaCl +Na 3 SmF 6 . In our previous works (3,(27)(28)(29)41,42), the transition state for electron transfer was achieved by simultaneous compression of the complex bonds as a result of a fullsymmetric oscillation and a certain shift of the boundary layer ions. Let us discuss how characteristics of the LUMO, the values of the LUMO and the HOMO energies and the activation barrier (E b ) change under such influences on the model system 18NaCl+Na 3 SmF 6 .…”

“…In these works, was suggested an outer-sphere mechanism of electron transfer in samarium-containing melts. To verify such hypotheses, it was advisable to use quantum-chemical simulations of the electron transfer process (3).…”

(Digital Presentation) Quantum Chemical Investigation of Samarium Complexes Stability in a Model System 18MX+M3SmX6 (X = F, Cl and M = Na, K, Rb, Cs)

“…Despite the low cost of machine time, it is not possible to estimate the interaction energy of the complex particle with the surrounding electrolyte ions using this approach. (11,(20)(21)(22)(23) This disadvantage is deprived of the second approach, which consists in analyzing interactions in an extended model system.…”