High‐Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Nickel Single‐Atom Catalysts with Tetradentate N 2 O 2 Coordination in a Three‐Phase Flow Cell

Carbon‐supported Ni II single‐atom catalysts with a tetradentate Ni‐N 2 O 2 coordination formed by a Schiff base ligand‐mediated pyrolysis strategy are presented. A Ni II complex of the Schiff base ligand ( R , R )‐(−)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine was adsorbed onto a carbon black support, followed by pyrolysis of the modified carbon material at 300 °C in Ar. The Ni‐N 2 O 2 /C catalyst showed excellent performance for the electrocatalytic reduction of O 2 to H 2 O 2 through a two‐electron transfer process in alkaline conditions, with a H 2 O 2 selectivity of 96 %. At a current density of 70 mA cm −2 , a H 2 O 2 production rate of 5.9 mol g cat. −1  h −1 was achieved using a three‐phase flow cell, with good catalyst stability maintained over 8 h of testing. The Ni‐N 2 O 2 /C catalyst could electrocatalytically reduce O 2 in air to H 2 O 2 at a high current density, still affording a high H 2 O 2 selectivity (>90 %). A precise Ni‐N 2 O 2 coordination was key to the performance.