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-N-3 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-N-3 sites through micropores (0.6 nm) and macropores (similar to 200 nm) interconnected by 50 nm channels. In a flow cell, Ni-N/OMC exhibits almost 100.0% CO Faraday efficiency (FECO) 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 1.5x10(5) 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-N-3 site can lower the energy of *COOH formation compared with that of the Ni-N-4 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.