High-Efficiency Electrocatalysis of Molecular Oxygen toward Hydroxyl Radicals Enabled by an Atomically Dispersed Iron Catalyst.

Fenton catalysis represents the promising technology to produce super-active ·OH for tackling severe water environment pollution issues, whereas it suffers from low atomic efficiency, poor pH adaptability, and catalyst non-reusability in a homogeneous or heterogeneous system. Here, single-atom iron catalysis is creatively introduced to drive electrochemical ·OH evolution utilizing earth-abundant oxygen and water as raw materials. The atomically dispersed iron settled by defective three-dimensional porous carbon (AD-Fe/3DPC) with unique C, Cl unsaturated coordination can efficiently tune the multi-electron oxygen reduction process, enabling O2-to-·OH conversion. The mass activity in ·OH production by AD-Fe/3DPC is almost two-orders of magnitude higher as compared to that by nanoparticular iron oxide catalyst. Meanwhile, the AD-Fe/3DPC electro-Fenton system exhibits fast elimination of refractory toxic pollutants, surpassing nanoparticular iron oxides in kinetic rate by 59 times or homogeneous Fenton by 10 times under similar experimental conditions. Experimental and theoretical results demonstrate that the remarkable enhanced mass activity of AD-Fe/3DPC in catalyzing O2 to ·OH is contributed by the synergistic effects of the maximized catalysis of atomically dispersed iron and the unique unsaturated coordination environment. The AD-Fe/3DPC catalytic system is demonstrated to be pH-universal, long-term stable, and well recyclable, truly satisfying flexible, sustainable, and green application of wastewater purification. This study gives a new sight into local coordination modulation of single-atom catalysts for selective electrocatalytic oxygen reduction.