In-situ investigation into the dynamic evolution of electrode surface H* and H* mediated pH-independent and residue-free electro-Fenton process

The practical use of Fenton process has been thus far limited by the harsh pH and accumulation of iron-rich sludge, while these two shortcomings will be tackled hopefully via developing non-metallic-catalyzed green Fenton-like approach. Herein, we investigate in-situ the dynamic evolution of electrode surface atomic hydrogen (H*) and H* mediated pH-independent and residue-free electro-Fenton process via operando electrochemical investigation and visualization techniques. The H* generated on the surface of palladium-coated electrode enables effective activation of hydrogen peroxide (H₂O₂) to generate hydroxyl radical (*OH) for efficient bisphenol A degradation (>99%), validated by in-situ cyclic voltammetry and electron spin resonance. Meanwhile, in-situ Raman spectra confirms that H₂O₂ is activated through a transition state of *H₃O₂ adduct with a low reaction energy barrier of 0.51 eV, whereby the lone electron in H* can readily cleave peroxide bond to produce [rad]OH and H₂O as the only products (ΔG = −1.03 eV). More importantly, the electron-driven H* production is independent of the solution pH as both H⁺ and H₂O can act as precursors verified by in-situ fluorescence analyses, so that the H₂O₂ activation mediated by H* extends successfully to a wider pH range (3–10). Our research provides a promising path toward eliminating restrictions of traditional Fenton process and paves the way simultaneously for in-situ investigation into reaction mechanism of such electrochemical processes. © 2023 Elsevier B.V. All rights reserved.