Electrochemical reduction of CO₂ to valuable chemicals offers a promising route for closing the carbon cycle. Among the products, CO is an important industrial feedstock. While nickel single-atom catalysts have shown high selectivity for CO production, they suffer from complex synthesis, instability at high current densities, and dynamic agglomeration. In a study published in ENG. Chem. Eng., researchers at East China University of Science and Technology and Guangxi University report a scalable catalyst design that overcomes these limitations using nickel nanoparticles encapsulated in a nitrogen-doped carbon shell on a hollow-rod carbon substrate.
The synthesis involved using rod-shaped graphitic carbon nitride as a structure-directing agent, with glucose forming a carbon shell via hydrothermal polymerization. After nickel loading and pyrolysis at 800 °C, Ni nanoparticles (~15 nm) were formed and encapsulated within a ~3.84 nm carbon layer, while a small fraction formed Ni–N coordination structures. The hollow-rod architecture, created by g-C₃N₄ decomposition, maximizes active site exposure.
XRD confirmed metallic Ni peaks (44.5°, 51.8°, 76.4°), while TEM showed lattice fringes of 0.201 nm corresponding to Ni(111). XPS and XANES/EXAFS confirmed Ni primarily in the zero-valent state with minor N coordination. The catalyst exhibited an Iᴅ/Iɢ ratio of 0.99, indicating high graphitization and good conductivity.
In an H-cell with 0.5 M KHCO₃, NiNP-BCN@C achieved a maximum CO Faradaic efficiency of 94.4 % at −0.83 V vs. RHE, maintaining >90 % from −0.73 to −1.03 V, with stable performance over 32 h. By contrast, the carbon substrate alone (BCN@C) showed negligible CO₂RR activity (FE_CO <1 %), while Ni nanoparticles without carbon shell protection (BCN@NiNP/C) achieved only 78.9 % FE_CO, confirming that the carbon shell effectively suppresses HER while preserving CO₂RR activity.
In a flow-cell configuration with 0.5 M KOH, NiNP-BCN@C achieved a CO Faradaic efficiency >98 % across a wide current density range of 140 to 300 mA·cm⁻², with a maximum turnover frequency of ~93,579 h⁻¹ at a low Ni loading of only 0.3425 wt %. Even under a reduced CO₂ concentration of 40 %, the catalyst maintained >90 % FE_CO, demonstrating robustness for practical applications using industrial flue gas.
In situ FTIR revealed intensified *COOH (1372 cm⁻¹) and COO⁻ (2400 cm⁻¹) peaks on NiNP-BCN@C compared to Ni single-atom counterparts at identical potentials, confirming superior CO₂ adsorption and activation. DFT calculations showed that N-doped carbon-encapsulated Ni exhibits stronger CO₂ affinity but weaker *H binding than bare Ni, explaining the suppressed HER and enhanced CO selectivity.
This work demonstrates that carbon-encapsulated nickel nanoparticles can serve as highly active and stable CO₂ reduction sites, offering a scalable and cost-effective design pathway for advanced electrocatalysts.
DOI
10.1007/s11705-026-2668-0