Asymmetrically ligated single atomic nickel sites for efficient hydrogen peroxide electrosynthesis

Atomic transition-metal-nitrogen-carbon electrocatalysts hold great promise as alternatives to benchmark Pt in the oxygen reduction reaction. The pristine metal centers with quasi square-planar D4h configuration, however, still suffer from unfavorable energetics and thereby strong activity/selectivity trade-off during the catalytic process. Here we present a ligand-field engineering of single-atom Ni-N-C catalysts to boost the sluggish kinetics via rationally constructing prototypical asymmetrically ligated Ni-N3O1 sites. The as-obtained Ni-supported multi-walled carbon nanotubes with molten salt-treated (defined as Ni/CNS) catalyst delivered an excellent H2O2 selectivity (> 90%) within a wide potential window (0.2–0.7 V vs. reversible hydrogen electrode (RHE)) and robust stability (for 10 h) in alkaline medium. Combined electron paramagnetic resonance and theoretical analysis rationalize this finding and demonstrate that the broken symmetry facilitates the electron transfer of a σ* to O-O orbital as compared to the Ni-N4 counterpart, playing an indispensable role in efficient O2 activation.