Electro-activating non-radical 1O2/H* via single atom manganese modified cathode: The indispensable role of metal active site Mn*

Highlights: • Non-radical (Mn*, ¹O₂, and H*) was first observed in the single atom Mn-SAC@PZS catalyst. • H* was produced by activating non-metallic active sites rather than metal Mn* active sites. • Highly selectively capturing and effectively degrading CIP in the presence of humic acid. • One-electron transfer process was the main ORR pathway (one-electron selectivity 72 ~ 100%). As an alternative to noble-metal Pt based catalysts, metal-based single atomic catalytic (SACs) exhibited excellent atom efficiency and catalytic activity via exposing abundant single atomic active centers. Here, we synthesized the monatomic Mn ligands anchored on porous N, P, S- co-doped carbon framework (Mn content over 4.5 wt%) (denoted as Mn-SAC@PZS). The single atomic Mn exhibited super mass activity (11.58 m² g⁻¹) and kinetic current (1.122$\times$10³ µA) with a much lower Tafel slope (4.25 mV dec⁻¹) at 0.792 V (vs. SCE). XANES and EXAFS revealed that the mononuclear Mn were inclined to coordinate with N and S rather than P to form the R space of Mn, in which the first coordination shells backscattered with Mn-N and Mn-S. RRDE revealed that one-electron ORR pathway (72 ~ 100%) dominated at the potential of 0.5 ~ 0.7 V, oxygen molecule was absorbed/activated on site Mn* to form O* intermediate, then further activated to ¹O₂ via one-electron ORR pathway, while H* was electro activated by non-metallic active sites (i.e. pyri-N, sp-N, -PN and SO). In addition, the Mn-SAC@PZS was capable of highly selectively capturing and effectively degrading CIP in the presence of HA. Fast and complete removal of CIP was achieved within 30 min in the Mn-SAC@PZS-EFLP system, and the apparent rate constant (k) was up to 0.25 min⁻¹. The energy consumption value was 0.453 kWh m⁻³, much lower than non-single atomic catalyst MnxOy@PZS (0.655 kWh m⁻³), which was comparable with the state-of-the-art advanced oxidation processes. These findings provided new insights into the maximum release of the atomic activity of the catalyst, and provides a possible way to selectively remove aromatics from multiple pollutants in complex water system.