Mechanism for Generating H₂ O₂ at Water-Solid Interface by Contact-Electrification

Area of Science:

• Interface Science
• Catalysis
• Physical Chemistry

Background:

• Contact-electrification at water-solid interfaces is increasingly studied.
• Electron transfers during contact-electrification can drive chemical reactions, a process termed contact-electro-catalysis (CEC).
• Chemically inert fluorinated polymers can function as single electrode electrochemical systems via CEC.

Purpose of the Study:

• To demonstrate hydrogen peroxide (H2O2) generation from air and deionized water using ultrasound-driven CEC with fluorinated ethylene propylene (FEP).
• To investigate the mechanism of H2O2 formation and radical propagation in solution.

Main Methods:

• Ultrasound-driven contact-electro-catalysis (CEC) using FEP as a catalyst.
• Kinetic rate measurements for H2O2 evolution.
• Electron paramagnetic resonance (EPR) spectroscopy to detect emitted electrons and radicals.
• Isotope labeling experiments to elucidate H2O2 formation pathways.
• Ab-initio molecular dynamic calculations to model radical reactions.

Main Results:

• H2O2 is generated from air and deionized water using FEP catalyst under ultrasound.
• High kinetic rates of H2O2 evolution were achieved (58.87 mmol L−1 gcat−1 h−1 at 20°C).
• EPR confirmed electron emission into solution by FEP and identified hydroxyl radicals (HO•) and superoxide radicals (O2•−).
• Ab-initio molecular dynamics revealed radical reactions occur via proton and electron exchange through water's hydrogen bond network (Grotthuss mechanism), challenging the traditional Brownian diffusion model.

Conclusions:

• Ultrasound-driven CEC using FEP effectively generates H2O2 from air and water.
• The Grotthuss mechanism, rather than Brownian diffusion, likely governs radical reactions in solution for H2O2 formation.
• This CEC mechanism offers a novel pathway for H2O2 generation and may be relevant in other natural and artificial systems.