A Novel Electrocatalytic Oxygen-Superoxide Pathway Driven by an Auxiliary Ligand-Engineered Nonheme Iron Catalyst for Highly Efficient Hydroxyl Radical Generation in Water Purification

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 H 2 O 2 generation and activation. Particularly, developing cathode-based electron transfer channels for the green activation of H 2 O 2 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 H 2 O 2 and superoxide radicals (O 2 •– ). A pathway was innovatively constructed in which the O 2 /O 2 •– redox couple was employed to transfer electrons from the cathode for activating in situ generated H 2 O 2 . Although the reaction between O 2 •– and H 2 O 2 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 O 2 •– . This work initiates a novel and sustainable pathway for highly efficiently activating H 2 O 2 via oxygen reduction intermediates for water purification at near-neutral conditions.