Equilibrium and Dynamical Characteristics of the Solvation Associated with the Li⁺/Li Redox Couple at the Ethylene Carbonate/Graphene Interface

Abstract

We present results from molecular dynamics simulations that describe structural and dynamical characteristics of the solvation pertinent to the Li + + e − → Li reduction reaction at the vicinity of the ethylene carbonate/electrode interface of an electrochemical cell kept at different electrical potentials. Polarization effects on the graphene electrodes due to fluctuations of the local solvent electric fields were explicitly incorporated. The first aspect that we investigated included a description of the spatial arrangements of solvent molecules in the first solvation shells of reactant and product species, complemented with the characterization of the local distributions of the charge allocated at the cathode. We also analyzed the characteristics of the fluctuations of the solvent vertical gaps as a means to examine the validity of Marcus linear hypotheses. In particular, we established a clear correspondence between departures from Gaussian models and infrequent modifications observed in the solute/solvent coordinations. Our dynamical analysis was focused on the examination of the solvation dynamics that follows a thermally activated, nonadiabatic electron transfer. The characteristic timescales describing the relaxations at the interfaces were found to be between 2 and 3 times slower than those registered following a related photoexcited electron transfer in the bulk. Predictions from the Onsager regression hypothesis to reproduce the solvation responses were also investigated.

Electrochemical Properties and Local Structure of the TEMPO/TEMPO+ Redox Pair in Ionic Liquids

“…A crucial impact of local environment of the solute on thermodynamics and kinetics of the electron transfer is known for relatively simple systems, such as metal ion redox couples in water or organic liquids. − In the case of a more complex solvent, ionic liquids, a dramatic role is played by their microheterogeneity and electrostrictive effects, as well as by viscosity, − though the latter can influence the kinetics of the electron transfer process not in a straightforward way …”