Nitrogen-doped carbon bilayer flow-through electrocatalytic membrane based on transition metal single atoms: Simultaneous generation and activation of H2O2 for ibuprofen degradation

The development of highly active and selective cathode materials is important for the in-situ synthesis of hydrogen peroxide (H₂O₂) and its activation to radicals for the degradation of emerging contaminants. In this paper, a nitrogen-doped carbon bilayer catalyst based on transition metal single atoms (Co₂-NC/Fe₃-C₃N₄) was developed to construct a flow-through electrocatalytic membrane system as the cathode for the efficient removal of ibuprofen (IBP) from wastewater. The active sites of high-density transition metal single atoms and heteroatoms N synergistically enhanced O₂ adsorption and *OOH desorption to promote H₂O₂ generation. The results showed that the actual contents of Fe and Co single atoms in the catalysts were 6.0 wt% and 4.2 wt%, which were higher than that of common single atoms < 3 wt%. The degradation rate of IBP in the Co₂-NC/Fe₃-C₃N₄ bilayer electrocatalytic membrane system could reach 93.1 % at 60 min under optimal conditions. The Fe₃-C₃N₄ layer produced H₂O₂ and further activated to hydroxyl radical (•OH) mainly through the three electron oxygen reduction reaction (3e^--ORR), whereas the Co₂-NC layer produced H₂O₂ through the 2e^--ORR to provide the precursors for the Fe₃-C₃N₄ layer for reactive oxygen species generation. The contribution of •OH was as high as 86.49 %, which was the main ROS for degrading IBP. The susceptible reaction sites of IBP were O9, O10, C1, and C11, and there were two main degradation pathways, and the toxicity of the degraded intermediates was reduced, which decreased the environmental risk generated by IBP.