Mechanism for Generating H₂O₂ at Water‐Solid Interface by Contact‐Electrification

Abstract

The recent intensification of the study of contact-electrification at water-solid interfaces and its role in physicochemical processes lead to the realization that electron transfers during water-solid contact-electrification can drive chemical reactions. This mechanism, named contact-electro-catalysis (CEC), allows chemically inert fluorinated polymers to act like single electrode electrochemical systems. This study shows hydrogen peroxide (H₂ O₂ ) is generated from air and deionized water, by ultrasound driven CEC, using fluorinated ethylene propylene (FEP) as the catalyst. For a mass ratio of catalyst to solution of 1:10000, at 20 °C, the kinetic rate of H₂ O₂ evolution reaches 58.87 mmol L^-1 g_cat ^-1 h^-1 . Electron paramagnetic resonance (EPR) shows electrons are emitted in the solution by the charged FEP, during ultrasonication. EPR and isotope labelling experiments show H₂ O₂ is formed from hydroxyl radicals (HO^• ) or two superoxide radicals (O₂ ^•- ) generated by CEC. Finally, it is traditionally believed such radicals migrate in the solution by Brownian diffusion prior to reactions. However, ab-initio molecular dynamic calculations reveal the radicals can react by exchanging protons and electrons through the hydrogen bonds network of water, i.e., owing to the Grotthuss mechanism. This mechanism can be relevant to other systems, artificial or natural, generating H₂ O₂ from air and water.