Tailoring Oxygen Reduction Selectivity for Acidic H₂O₂ Electrosynthesis on Single-Atom Co-N-C Catalyst via PEG...

The selective two-electron oxygen reduction reaction (ORR) for H₂O₂ electrosynthesis provides a promising alternative to anthraquinone-based redox technology. However, atomically dispersed Co-N-C materials routinely lead the ORR process to follow a four-electron path via accessible Co-N₄ moieties rather than terminating in competitive H₂O₂ production. Herein, we demonstrate that by simultaneously reconstructing Co-N₂-C and modifying oxygen functional groups into a Co-adjacent carbon matrix through low-temperature pyrolysis with oxygen-containing molecules, a Co SAC four-electron catalyst with typical Co-N₄ sites can be transformed into a Co SAC-PEG electrocatalyst with high H₂O₂ selectivity. A combination of X-ray absorption and infrared spectroscopy confirmed that the shift in ORR selectivity from the four-electron pathway to the two-electron pathway originated from the transfer of the real active sites from rigid in-plane embedded Co-N₄ to the oxygen functional groups modified with low-coordinated Co-N₂-C for Co SAC-PEG. In stark contrast to the remarkable 4e^- prototype Co SAC, the Co SAC-PEG after treatment has a surprising E_onset and selectivity for H₂O₂ electrosynthesis in acidic electrolytes. This study presents a new avenue for the selective manipulation of the ORR pathway via tailoring the flexible structure of single Co sites by a one-step post treatment process, ultimately converting the readily available 4e^- catalyst directly into a difficult-to-obtain 2e^- catalyst.