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Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
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Diffusional motion of redox centers in carbonate electrolytes
Kee Sung Han1, Nav Nidhi Rajput2, Xiaoliang Wei3
1Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
The Journal of Chemical Physics
|September 15, 2014
Summary
Self-diffusion coefficients of ferrocene derivatives in carbonate solvents were measured using NMR spectroscopy. Results show concentration-dependent diffusion and solvent interactions, with simulations providing molecular insights.
Area of Science:
- Electrochemistry
- Materials Science
- Physical Chemistry
Background:
- Understanding ion transport in electrolytes is crucial for battery performance.
- Ferrocene derivatives offer redox activity and tunable properties for electrochemical applications.
- Carbonate solvents like EC, PC, and EMC are common in lithium-ion batteries.
Purpose of the Study:
- To measure self-diffusion coefficients (D) of ferrocene (Fc) and N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium bistrifluoromethyl-sulfonimide (Fc1N112-TFSI) in carbonate solvents.
- To investigate the effect of Fc1N112-TFSI concentration and temperature on diffusion.
- To compare experimental NMR data with molecular dynamics (MD) simulations for molecular-level understanding.
Main Methods:
- (1)H and (19)F pulsed field gradient nuclear magnetic resonance (NMR) spectroscopy to measure self-diffusion coefficients.
- Classical molecular dynamics (MD) simulations to model diffusion behavior.
- Variable temperature (0-50 °C) and concentration (0.25-1.7 M) studies.
Main Results:
- Self-diffusion coefficients (D) decreased with increasing Fc1N112-TFSI concentration.
- D(TFSI-) was larger than D(Fc1N112+) due to fluoromethyl groups.
- Stronger interaction between propylene carbonate (PC) and Fc1N112(+) was observed, affecting its diffusion and solvent viscosity.
- In saturated solutions, solvent diffusion coefficients became equal, indicating limited free volume.
Conclusions:
- Experimental and simulation results agree, providing molecular insights into solvation structure.
- Interactions between Fc1N112(+) and PC influence electrolyte transport properties.
- Diffusion behavior is concentration and temperature-dependent, critical for electrolyte design.
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