Ionothermal Carbonization of Biomass to Construct Fe, N‑Doped Biochar with Prominent Activity and Recyclability as Cathodic Catalysts in Heterogeneous Electro-Fenton

Heterogeneous electro-Fenton is an efficient advanced oxidation process for the degradation of refractory organic contaminants in wastewater, and its efficiency is governed by cathodic catalysts. In this work, the Fe, N doped biochar materials (Fe/N/biochar) were synthesized via a simple ionothermal carbonization of biomass and used as a cathodic catalyst for heterogeneous electro-Fenton. The as-synthesized biochar materials with uniform doping of N and Fe significantly improved the performance of the electro-Fenton process via promoting the two-electron transfer oxygen reduction reaction for H₂O₂ production and subsequent H₂O₂ activation for reactive oxygen species (e.g., ^•OH and ^•O₂^–) generation. The Fe, N doped biochar catalyst showed excellent recyclability in the cycle runs of the electro-Fenton process, in which its catalytic activity did not fade but continuously increased. Based on the ex situ high resolution transmission electron microscopy and electron paramagnetic resonance results, more active catalytic site exposure was induced by the interfacial crystalline-phase transformation and contributed to the excellent recyclability of the catalyst. This work will provide new insights into the rational design and synthesis of efficient electro-Fenton catalysts with a prominent activity and recyclability.