Co-catalytic application of in situ encapsulation nickel nanoparticles and nickel single atoms on nitrogen-rich carbon frameworks enable efficient and selective CO2 electroreduction.

Carbon dioxide, as one of the major greenhouse gases, has been widely recognized as a key driver of extreme climate changes. Efficiently converting CO2 into valuable resources through reduction reactions stands as a strategic challenge for the future. Graphitic carbon nitride (g-C3N4) holds great promise as a catalyst support for CO2 reduction reactions (CO2RR), but its commercial practical application is hindered by low electrical conductivity and hydrophobicity. This study presents an innovative structural modulation strategy: integrating g-C3N4 with nitrogen-doped carbon nanotubes (N-CNTs) in situ catalytically grown by nickel nanoparticles. This unique interpenetrating architecture creates a hierarchical dual-pathway conductive system, boosting charge transport and hydrophilicity. The catalytic superiority stems from synergistic dual active centers: nickel nanoparticles encapsulated in carbon shells (Ni-NPs@C) and nickel single atoms (Ni-SAs) anchored on g-C3N4. Ni-SAs serve as primary CO2 adsorption/activation sites, while Ni-NPs@C accelerate electron transfer. Importantly, the carbon shell encapsulation of Ni-NPs uniquely suppresses the hydrogen evolution reaction. The obtained catalyst achieves a CO Faradaic efficiency of over 98 % with stable performance for 40 h in an H-cell. In MEA reactors, the catalyst demonstrates a CO Faraday efficiency of 85 % at an industrially current density of 780 mA cm-2. In flow cell reactors, the catalyst maintains current densities exceeding 100 mA cm-2 over a wide potential range from -0.6315 V to -1.1315 V (vs. RHE), with CO Faradaic efficiencies consistently above 90 %. This green, one-pot synthesis balances activity, selectivity, and stability, offering a scalable paradigm for next-generation sustainable electrocatalysts.