Nitrogen Doping-Induced Weak Metal–Support Interaction Regulating the Interfacial Behavior of Hydroxyl Radicals in the Electro-Fenton Process

Metal–support interaction critically influences the activity and stability of heterogeneous catalysts, yet its role in heterogeneous electro-Fenton (HEF) processes─which involve strong oxidizing conditions and multielectron transfer reactions─remains poorly understood. In this study, we synthesized a FeCo dual-atom catalyst via intermolecular interactions between the model molecule FePc/CoPc and a nitrogen-rich carbon substrate (FeCo-DAC-N), delivering efficient catalytic performance for the HEF process. To elucidate the role of this weak metal–support interaction, a control catalyst (FeCo-DAC-C) was prepared by pyrolyzing FeCo-DAC-N under N2, thereby anchoring the metal sites directly into the carbon matrix. Despite having identical metal content, FeCo-DAC-N with this weak metal–support interaction outperformed in all dimensions, including RhB removal, H2O2 activation, H2O2 accumulation, and •OH generation. Cycling tests, metal leaching quantification, and in situ Raman characterization collectively suggested the improved stability of FeCo-DAC-N. Shell-isolated nanoparticle-enhanced Raman spectroscopy disclosed distinct peaks belonging to the adsorbed •OH (Fe–OH*, 563 cm–1) and OH– (Fe–OH, 445–450 cm–1) on the Fe site in FeCo-DAC-C-catalyzed HEF, respectively. Surprisingly, this typical Fe–OH* signal cannot be recognized in that of FeCo-DAC-N. Instead, a high-intensity and broad peak with a vacillating peak location (457–468 cm–1) under different electrode potentials was observed, which can be attributed to the overlap of Fe–OH* and Fe–OH peaks. The altered interfacial behavior of Fe–OH* was corroboratively evidenced by quenching experiments in which n-butanol caused more significant inhibition of RhB degradation. Furthermore, density functional theory calculations confirmed a lower energy barrier for H2O2 activation and stronger Fe–OH adsorption when Fe–N sites interact with the nitrogen support, which is consistent with experimental observations. This work presents a primary effort to elucidate the role of the weak metal–support interaction in regulating the interfacial behavior of •OH in the HEF process, which should deepen the understanding of the electro-Fenton process and inspire the rational design of next-generation catalysts.