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

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 Eonset 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.