External-Shell Oxygen Enabling the Local Environment Modulation of Unsaturated NbN 3 for Efficient Electrosynthesis of Hydrogen Peroxide

Single atom catalysts with tunable coordination structure have shown grand potential in flexibly altering the selectivity of oxygen reduction reaction (ORR) towards desired pathway. However, the local coordination number modulation on the single metal sites, which could mediate the ORR pathway, still remains challenging. Herein, we prepare the Nb single atom catalysts (SACs) with external-shell oxygen modulated unsaturated NbN 3 site in carbon nitride and NbN 4 site anchored in nitrogen doped carbon carriers, respectively. Compared with typical NbN 4 moieties for 4e -ORR, the as prepared NbN 3 SACs exhibits excellent 2e -ORR activity in 0.1 M KOH, of which the onset overpotential close to zero (9 mV) and the H 2 O 2 selectivity surpass 95%, making it one of the state-of-the-art catalysts in electrosynthesis of hydrogen peroxide. DFT theoretical calculations indicate the unsaturated Nb-N 3 moieties and adjacent oxygen groups optimize the interface bond strength of pivotal intermediates (OOH*) for producing H 2 O 2 , thus accelerating 2e -ORR pathway. Our findings may provide novel platform for developing SACs with high activity and tunable selectivity.