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.
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