Electron Spin Resonance Evidence for Electro-generated Hydroxyl Radicals.

Area of Science:

• Environmental Chemistry
• Electrochemistry
• Analytical Chemistry

Background:

• Hydroxyl radicals (•OH) are key oxidants in electrochemical advanced oxidation processes (EAOP).
• Direct electron transfer (DET) reactions and side reactions of spin traps like DMPO complicate ESR identification of •OH.
• Lack of direct ESR evidence for electro-generated •OH under anodic polarization.

Purpose of the Study:

• To provide direct ESR identification of electro-generated •OH in EAOP.
• To establish kinetic conditions for effective spin trapping and ESR identification.
• To quantify •OH formation and investigate its dependence on electrolysis parameters.

Main Methods:

• Employing kinetic selection by excessive addition of DMPO and fast spin trapping.
• Utilizing electron spin resonance (ESR) spectroscopy for radical identification.
• Quantifying •OH using ESR and verifying with a terephthalic acid probe.

Main Results:

• Successful ESR identification of electro-generated •OH using optimized DMPO spin trapping.
• Quantified •OH formation at 47.84 ± 0.44 μM on a TiSO anode at 10 mA cm⁻².
• Demonstrated positive dependence of •OH formation on electrolysis time, current density, and anode potential.

Conclusions:

• Direct ESR evidence confirms electro-generated •OH formation in EAOP.
• The developed method allows for quantification of •OH and screening of anode materials.
• This work provides fundamental insights into •OH generation mechanisms in EAOP.