Surface Science of Intercalation Materials and Solid Electrolytes by René Hausbrand

Author:René Hausbrand
Language: eng
Format: epub
ISBN: 9783030528263
Publisher: Springer International Publishing

The oxidation potentials as evaluated above using essentially a Born-type of cycle as is also commonly done for redox electrons [46] do not explicitly consider the distribution of electronic states in the electrolyte. The distribution of electronic states is treated by the Marcus model, which states that the electronic levels of reduced and oxidized species are separated due to solvent reorganization and are subject to statistical broadening due to fluctuations of the solvent shell [46, 54]. Figure 5.16 illustrates the electronic states in the condensed solvent phase according to the Marcus model with a reference to the vacuum level. Additional states due to the presence of salt are also indicated. With an energy level diagram as shown, the oxidation potential can be specified by the position of the high energy tail of the HOMO states. Important factors for the position and distribution of the states are the ionization potential of a gaseous molecule, relevant polarization effects as well as thermal broadening. Also, the interaction of the molecules in the condensed phase is expected to have an influence, which should remain small, however (few tenth of eV).

Fig. 5.16Illustration of the effective position of solvent HOMO states in the condensed phase with respect to the vacuum level (EVac) and related oxidation potential (Eox). The main factors are the ionization potential of the gaseous molecule (IP) and the polarization which occurs during electron transfer (Epol). Also, a possible energy shift due to the interactions in the condensed phase is indicated (ΔE, shaded area). The presence of salt results in additional states (HOMO′), which can significantly reduce the oxidation potential.

Reprinted from [34], with permission of AIP Publishing

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