Efficient electro-Fenton processes on a novel self-supported single-atom Fe electrode: Mechanism and practical application

Electro-Fenton technology is widely applied in the field of water treatment for refractory organic pollutant degradation. Herein, a novel self-supported single-atom Fe electrode was fabricated via simple electrodeposition and pyrolysis approach for the first time. The prepared single-atom electrode showed excellent activity and stability for degradation of aromatic compounds in electro-Fenton (EF) process, in which the 4-hydroxybenzoic acid (4-HBA) pollutant is completely decomposed by the substitution, decarboxylation, hydroxylation, and oxidation reactions. Significantly, the electrode possessed great performance for purification of the shale gas fracturing flowback fluid. The degradation pathways of organics in real matrix were also studied in detail. The characterization analysis proved that the single-atom Fe was in situ grown on electrode surface, confirming to be Fe-N/O construction with coordination number of ∼4.3. Therefore, the EF mechanism was preliminary proposed by analyzing all possible configurations of single-atom Fe (FeN₄, FeN₃O₁, FeN₂O₂, and FeN₁O₃). Results implied that the FeN₂O₂ structure may contribute to improving EF performance by enhancing the O₂ adsorption and promoting the breakage of *–OOH to form H₂O₂. Additionally, the good adsorption of FeN₂O₂ toward organic pollutant was also greatly conducive to the EF degradation. This study provides a feasible strategy for self-supported single-atom Fe electrode and demonstrated its application for efficient EF treatment of real wastewater.