A Dynamically Stabilized Single-Nickel Electrocatalyst for Selective Reduction of Oxygen to Hydrogen Peroxide

On-location electrochemical generation of H₂ O₂ is of great current interest. Herein, selective two-electron reduction of O₂ to H₂ O₂ by a single [Ni^II (H₂ O)₆ ]²⁺ cation that is dynamically associated with a negatively charged metal-organic layer (MOL) by hydrogen bonding and coulombic interactions is reported. In contrast, Ni^II centers covalently immobilized on the MOL reduce O₂ to H₂ O in a four- electron process. Oxygen adsorption by [Ni^II (H₂ O)₆ ]²⁺ followed by two-electron reduction generates neutral [Ni^II (H₂ O)₄ (OH)(OOH)]⁰ , which momentarily disconnects from the negatively charged MOL to avoid the injection of additional electrons. Release of H₂ O₂ from [Ni^II (H₂ O)₄ (OH)(OOH)]⁰ regenerates [Ni^II (H₂ O)₆ ]²⁺ , which regains affinity to the MOL. Such dynamically associated Ni^II single-metal electrocatalysts ensure high selectivity and represent a new strategy for generating selective catalysts for electrochemical production of important chemicals.