Microfluidic channel flow cell for simultaneous cryoelectrochemical electron spin resonance

Area of Science:

• Electrochemistry
• Spectroscopy
• Chemical Engineering

Background:

• Electron spin resonance (ESR) spectroscopy is crucial for studying radical species.
• In situ measurements under variable temperature conditions present unique challenges for flow cells.
• Existing flow-through systems are incompatible with certain variable temperature apparatus.

Purpose of the Study:

• To develop and characterize a novel microfluidic electrochemical channel flow cell for ESR spectroscopy.
• To enable in situ operation within a cylindrical resonant ESR cavity under variable temperatures.
• To analyze unstable radical species and improve spectral resolution at low temperatures.

Main Methods:

• Construction of a U-tube configuration microfluidic electrochemical channel flow cell with gold electrodes.
• In situ operation within a TE011 resonant ESR cavity under variable temperature conditions.
• Characterization using p-bromonitrobenzene reduction and validation via 3D digital simulation of concentration profiles.
• Acquisition of ESR spectra for various radical species at 233 K.

Main Results:

• The microfluidic cell was successfully constructed and operated in situ.
• The cell's performance was validated using a model system and digital simulation.
• ESR spectra of unstable radical species (m- and p-iodonitrobenzene, o-bromonitrobenzene, m-nitrobenzyl chloride) were obtained at 233 K.
• Improved spectral resolution was observed for 2-chloranthraquinone radical anion and crystal violet radical at low temperatures.

Conclusions:

• The novel microfluidic electrochemical flow cell is suitable for in situ variable temperature ESR studies.
• The cell facilitates the investigation of transient radical species previously difficult to analyze.
• The developed system enhances ESR spectral resolution at low temperatures, opening new avenues for radical research.