Highly efficient electroreduction of CO2 by defect single-atomic Ni-N3 sites anchored on ordered micro-macroporous carbons.

Microporous supports typically fail to fully expose active sites for electrolytes and CO₂ molecules, and this usually results in low current density for the electrocatalytic CO₂ reduction reaction (CO₂RR). To overcome the biggest obstacle and facilitate commercial applications, defective single-atomic Ni-N₃ sites anchored to ordered micro-macroporous N-doped carbon (Ni-N/OMC) have been prepared by the pyrolysis of the Ni-ZIF-8@PS (ZIF = zeolitic imidazolate framework) and are intended to provide enhanced CO₂RR with a current density at an industrial level. This Ni-ZIF-8@PS is constructed of nickel-based ZIF-8 embedded in the three-dimensional (3D) highly ordered polystyrene spheres (PS). The 3D ordered micro-macroporous architecture of Ni-N/OMC could facilitate the mass transfer of substrates to the accessible defective single-atomic Ni-N₃ sites through micropores (0.6 nm) and macropores (∼200 nm) interconnected by 50 nm channels. In a flow cell, Ni-N/OMC exhibits almost 100.0% CO Faraday efficiency (FE_CO) between −0.2 and −1.1 V vs. RHE and an industrial level CO partial current density of 208 mA cm⁻². It has a turnover frequency of 1.5×10⁵ h⁻¹ at −1.1 V vs. RHE in 1 M KOH electrolyte, which exceeds that of most reported nickel-based electrocatalysts. This excellent CO₂RR performance for Ni-N/OMC makes it a state-of-the-art electrocatalyst for CO₂RR. Theoretical calculations show that the defective Ni-N₃ site can lower the energy of *COOH formation compared with that of the Ni-N₄ site, thereby accelerating CO₂RR. Ni-N/OMC can also be utilized as a cathodic catalyst in Zn-CO₂ battery, exhibiting high CO selectivity in the discharge process and excellent stability. This work paves a pathway to rational design of highly efficient electrocatalysts with 3D hierarchically ordered micro-macroporous architecture for CO₂RR towards industrial production and commercial applications. [ABSTRACT FROM AUTHOR]