Heterostructure of Fe₃O₄ Confined in Hierarchical Porous Carbon for Interface‐Enhanced Medical‐Grade H₂O₂ Electrosynthesis

The electrocatalytic two-electron oxygen reduction reaction (2e^- ORR) presents an environmentally sustainable approach to produce hydrogen peroxide (H₂O₂). Heterostructures coupling non-noble transition metal oxides (TMOs) with carbon materials hold promise for 2e^- ORR, but face challenges in controlling morphology, phase composition, and active centers. In this study, a hierarchically porous tremella-like heterojunction characterized by ultrafine cubic Fe₃O₄ nanoparticles within the amorphous carbon (UFe₃O₄@HPAC) is obtained using the integrated platform of green Fe-based deep eutectic solvent via a two-step annealing process. UFe₃O₄@HPAC exhibits remarkable overall and intrinsic 2e^- ORR activity, delivering 96% H₂O₂ selectivity and a turnover frequency (TOF) of 67.5 s^-1. Notably, UFe₃O₄@HPAC possesses superior H₂O₂ production capabilities, showing long-term stability of 100 h with a H₂O₂ production rate of 8.1 g L^-1 h^-1 in flow-cell, while achieving various medical-grade H₂O₂ concentrations (3.0-7.8 wt%). Additionally, integrating on-site H₂O₂ production with electro-Fenton achieved rapid decomposition of contaminants. The unique heterostructure, with the synergistic effect of Fe₃O₄ and amorphous carbon, enhances electronic conductivity. Moreover, the electronic redistribution at the interface of the heterostructure triggers the thermodynamically favorable multiple active sites of Fe and C centers for the 2e^- ORR. This work offers a new perspective on transition metal-based materials for H₂O₂ production.