O, N Coordination-Mediated Nickel Single-Atom Catalysts for High-Efficiency Generation of H₂O₂

Abstract

Electrochemical selective two-electron oxygen reduction shows great potential for on-site electrochemical production of hydrogen peroxide (H₂O₂). Herein, we demonstrated the synthesis of Ni single-atom sites coordinated by three oxygen atoms and one nitrogen atom (i.e., Ni-N₁O₃) supported by oxidized carbon black (OCB) by pyrolyzing nickel-(pyridine-2,5-dicarboxylate) coordination complexes. Aberration-corrected scanning transmission electron microscopy (AC-STEM) combined with X-ray absorption spectroscopy (XAS) proves the presence of atomically dispersed Ni atoms attached on OCB (labeled as Ni-SACs@OCB), in which Ni single atoms are stabilized by a N, O-mediated coordination configuration. This Ni-SACs@OCB catalyst shows high H₂O₂ selectivity (95%) in a range of 0.2-0.7 V undergoing a two-electron oxygen reduction process, with a kinetic current density of 2.8 mA cm^-2 and a mass activity of 24 A g_cat.^-1 at 0.65 V (vs RHE). In practice, H-cells with Ni-SACs@OCB as catalysts displayed a high H₂O₂ production rate of 98.5 mmol g_cat.^-1 h^-1 with negligible current loss during testing, suggesting the high H₂O₂ generation efficiency and robust stability. DFT theoretical calculations revealed that Ni single-atom sites coordinated by O, N coordination exhibit advantages in oxygen adsorption and increased reactivity toward the intermediate species, *OOH, which is beneficial to high selectivity for H₂O₂ production. This work provides a novel N, O-mediated four-coordinate nickel single-atom catalyst as a promising candidate for practical decentralized production of H₂O₂.