Scanning Electrochemical Microscopy for Kinetic Investigations in Viscous Deep Eutectic Solvents: Identifying...

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• High-performance redox flow batteries require understanding heterogeneous electrochemical electron transfer (ET) kinetics.
• Concentrated hydrogen-bonded electrolytes (CoHBEs), including deep eutectic solvents (DESs), are promising but challenging due to viscosity.
• Traditional Tafel analysis is limited by mass transfer issues in viscous electrolytes.

Purpose of the Study:

• To develop and validate a scanning electrochemical microscopy (SECM) methodology for evaluating ET kinetics in viscous DES.
• To overcome limitations of traditional methods in analyzing complex electrolyte systems.
• To investigate the Fe3+/Fe2+ redox couple kinetics in ethaline DES.

Main Methods:

• Utilized SECM for precise tip positioning and feedback response analysis in ethaline DES.
• Employed Lattice Boltzmann Method (LBM) simulations to model fluid dynamics, concentration fields, and tip geometry effects.
• Validated a reliable SECM tip positioning point (NiT = 2 at L = 0.7) for accurate kinetic studies.

Main Results:

• Successfully established SECM tip positioning protocols in viscous ethaline DES, yielding pseudopositive feedback.
• Demonstrated that SECM can accurately recreate approach curves under various conditions, independent of tip velocity.
• Observed nonideal kinetic behavior for the Fe3+/Fe2+ couple in ethaline DES, potentially due to solvent dynamics or chloride anion interactions.

Conclusions:

• SECM is a robust technique for characterizing ET kinetics in challenging, viscous DES electrolytes.
• The findings provide a foundation for optimizing DES electrolytes for high-performance batteries.
• Further research is needed to elucidate the factors contributing to the observed nonideal kinetics in DES.