Single-Crystalline Ionic ZIF-8 Derived Long Ni─N Bonded Ni─N─C Configuration for Efficient Electroreduction of CO2 to CO

Abstract

N-doped carbon-supported single-atom metal sites (Me−N−C) have emerged as promising candidates for electrochemical CO₂ reduction reaction (CO₂RR) under industrial current densities. However, rationalizing their local coordination environment remains challenging. Herein, a feasible strategy is demonstrated for constructing robust Ni─N─C centers by designing a new family of single-crystalline ionic ZIF-8 materials with atomically defined ionic liquid (IL) cations inside the microchannels. The ─COOH tethered ionic ZIF-8 directed the formation of atomically dispersed Ni─N₄ sites with an elongated Ni─N bond of 1.94 Å. The resulting Ni─N─C catalyst effectively catalyzed the electrochemical CO₂ reduction to CO, delivering a partial current density of 679 mA cm⁻² with a Faradic efficiency of 97% and achieving a maximum turnover frequency of 106197 h⁻¹. The extended Ni─N bond enables the slightly reduced valence state of the Ni site, optimizing the affinity toward CO₂ and intermediate, and thus lowering the energy barrier in the rate-determining ^*CO₂ → ^*COOH step.