As a chemical-free and post-treatment-free technology, electrocatalytic oxygen activation to efficiently obtain hydroxyl radicals is critical for recalcitrant organic removal in wastewater. However, its potential is hindered by the lack of dual-functional cathode materials for simultaneously achieving efficient in situ H2O2 generation and activation. Particularly, developing cathode-based electron transfer channels for the green activation of H2O2 without Fe(II) regeneration presents significant challenges. Here, we designed a nonheme iron catalyst, which employs polypyrrole as an auxiliary ligand to direct the reduction of oxygen into H2O2 and superoxide radicals (O2•-). A pathway was innovatively constructed in which the O2/O2•- redox couple was employed to transfer electrons from the cathode for activating in situ generated H2O2. Although the reaction between O2•- and H2O2 is typically considered unfeasible traditionally due to the slow rate, the energy barrier was lowered to 48% and kinetically accelerated through biomimetic electrocatalysis, which led to a 370% enhancement in water purification efficiency. We confirmed that only the presence of coordination between the auxiliary ligand and the nonheme iron catalyst can obtain the formation of O2•-. This work initiates a novel and sustainable pathway for highly efficiently activating H2O2 via oxygen reduction intermediates for water purification at near-neutral conditions.
Keywords: Haber−Weiss reaction; auxiliary ligand; biomimetic electrocatalysis; oxygen reduction; superoxide (O2•−).