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.