The selective 3e- ORR pathway induced by differential polarization of surface -OH by adjacent heterodinuclear metals realizes the directed conversion of radicals

Abstract

Chlorophenol pollutants are listed as global priority control substances due to their strong carcinogenicity and difficult biodegradability. The advanced oxidation technology based on •OH has strong oxidizability superior to other oxygen-active substances, and has become a favorable candidate for the treatment of organic pollutants in the environmental field. Among them, electrocatalytic two-electron ORR is widely used in water environment treatment as a typical electrochemical advanced oxidation (EAOP) technology. Under normal conditions, molecular oxygen (O₂) can be selectively reduced to hydrogen peroxide (H₂O₂) by ORR two-electron reaction, and then further forms efficient hydroxyl radicals (•OH), which is used to target various refractory micropollutants.However, the electro-Fenton (EF) process faces challenges such as slow O₂ adsorption and activation, slow O-O bond cleavage, and slow ORR kinetics on the cathode due to the dissolution of metal ions. In the ORR reaction, the terminal adsorption of ∗OOH intermediates on the active site is difficult to achieve independent regulation, resulting in a slow kinetic process of directional conversion from hydrogen peroxide to hydroxyl radicals.Therefore, the removal efficiency of organic pollutants in EF process is seriously restricted by the above factors.This thesis proposes a kinetic optimization strategy based on the synergistic effect of heteronuclear bimetallic catalysts and the polarization of surface hydroxyl groups (-OH). By constructing a cobalt-iron layered double hydroxide (CoFe-LDHs) catalyst, we significantly enhance the selective generation of hydroxyl radicals along the oxygen reduction reaction (ORR) pathway, achieving efficient degradation of refractory organic pollutants such as 4-chlorophenol (4-CP). Our research reveals that CoFe-LDHs form a Fe-O-Co bridging structure through electron transfer between Fe³⁺ and Co²⁺, which induces asymmetric adsorption of the O-O bond and lowers the kinetic energy barrier for O-O coupling (forming MxO-HOOH intermediates). This enables the directed conversion of •OH at low overpotentials. Therefore, the kinetic optimization strategy for catalysts based on modulating the adsorption of intermediates at active sites is not only of significant importance in current research but also provides new ideas and directions for future catalyst design and development.In particular, it shows broad application prospects in the fields of energy conversion and storage, environmental pollution control and so on.

Keywords: Electrocatalysis; Heterobimetallic synergy; Hydroxyl radical; Oxygen reduction reaction.