High‐Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Nickel Single‐Atom Catalysts with Tetradentate N₂O₂ Coordination in a Three‐Phase Flow Cell

Abstract

Carbon-supported Ni^II single-atom catalysts with a tetradentate Ni-N₂ O₂ 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-N₂ O₂ /C catalyst showed excellent performance for the electrocatalytic reduction of O₂ to H₂ O₂ through a two-electron transfer process in alkaline conditions, with a H₂ O₂ selectivity of 96 %. At a current density of 70 mA cm^-2 , a H₂ O₂ 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-N₂ O₂ /C catalyst could electrocatalytically reduce O₂ in air to H₂ O₂ at a high current density, still affording a high H₂ O₂ selectivity (>90 %). A precise Ni-N₂ O₂ coordination was key to the performance.