Diffusional motion of redox centers in carbonate electrolytes

Journal Article · Sun Sep 14 00:00:00 EDT 2014 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4894481· OSTI ID:22308384

Han, Kee Sung ^[1]; Rajput, Nav Nidhi; Persson, Kristin A. ^[2]; Wei, Xiaoliang; Wang, Wei ^[3]; Hu, Jian Zhi ^[4]

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1. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)
2. Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
3. Energy and Environmental Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)
4. Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

Ferrocene (Fc) and N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium bistrifluoromethyl-sulfonimide (Fc1N112-TFSI) were dissolved in carbonate solvents and self-diffusion coefficients (D) of solutes and solvents were measured by {sup 1}H and {sup 19}F pulsed field gradient nuclear magnetic resonance (NMR) spectroscopy. The organic solvents were propylene carbonate (PC), ethyl methyl carbonate (EMC), and a ternary mixture that also includes ethylene carbonate (EC). Results from NMR studies over the temperature range of 0–50 °C and for various concentrations (0.25–1.7 M) of Fc1N112-TFSI are compared to values of D simulated with classical molecular dynamics (MD). The measured self-diffusion coefficients gradually decreased as the Fc1N112-TFSI concentration increased in all solvents. Since TFSI{sup −} has fluoromethyl groups (CF{sub 3}), D{sub TFSI} could be measured separately and the values found are larger than those for D{sub Fc1N112} in all samples measured. The EC, PC, and EMC have the same D in the neat solvent mixture and when Fc is dissolved in EC/PC/EMC at a concentration of 0.2 M, probably due to the interactions between common carbonyl structures within EC, PC, and EMC. A difference in D (D{sub PC} < D{sub EC} < D{sub EMC}), and both a higher E{sub a} for translational motion and higher effective viscosity for PC in the mixture containing Fc1N112-TFSI reflect the interaction between PC and Fc1N112{sup +}, which is a relatively stronger interaction than that between Fc1N112{sup +} and other solvent species. In the EC/PC/EMC solution that is saturated with Fc1N112-TFSI, we find that D{sub PC} = D{sub EC} = D{sub EMC} and Fc1N112{sup +} and all components of the EC/PC/EMC solution have the same E{sub a} for translational motion, while the ratio D{sub EC/PC/EMC}/D{sub Fc1N112} is approximately 3. These results reflect the lack of available free volume for independent diffusion in the saturated solution. The Fc1N112{sup +} transference numbers lie around 0.4 and increase slightly as the temperature is increased in the PC and EMC solvents. The trends observed for D from simulations are in good agreement with experimental results and provide molecular level understanding of the solvation structure of Fc1N112-TFSI dissolved in EC/PC/EMC.

• OSTI ID: 22308384
• Journal Information: Journal of Chemical Physics, Vol. 141, Issue 10; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBONATES
CARBONIC ACID ESTERS
CARBONYLS
COMPARATIVE EVALUATIONS
ELECTROLYTES
ETHYLENE
FERROCENE
MOLECULAR DYNAMICS METHOD
NUCLEAR MAGNETIC RESONANCE
ORGANIC SOLVENTS
PULSES
SELF-DIFFUSION
SIMULATION
SOLUTES
SOLUTIONS
SOLVATION
SPECTROSCOPY
STRONG INTERACTIONS