Directing three-electron oxygen reduction to hydroxyl radicals via encapsulated Fe0 and FeOx in carbon shells for rapid organics degradation

Abstract

Electro-Fenton is a promising technology for the treatment of organic wastewater via the in-situ generation of highly oxidizing hydroxyl radicals (·OH). However, The Fe(III)/Fe(II) constitutes the rate-limiting step in the entire electro-Fenton process, where sluggish Fe(III)/Fe(II) severely constrains the generation rate of ·OH. Herein, we designed a three-electron oxygen reduction reaction (3e^- ORR) catalyst featuring an iron core encased in porous carbon (Fe@PC), which accelerates the Fe(III)/Fe(II) cycle, directly reduces O₂ to ·OH, and thus shows excellent phenol removal efficiency. Results show that the H₂O₂ in situ generated on the carbon shell can be rapidly activated by the Fe/FeO_x core, leading to the increased ·OH generation. Consequently, the as-developed Fe@PC electro-Fenton system exhibits higher phenol degradation activity, with a kinetic constant of 0.092 min⁻¹, which is more than 10 times higher than the porous carbon (PC) counterpart. This study contributes to the rational design of 3e^- ORR catalysts with the aim of strengthening the practical application of electro-Fenton in the treatment of organic wastewater.