Single‐Step Conversion of Metal Impurities in CNTs to Electroactive Metallic Nitride Nanoclusters for Electrochemical CO ₂ Reduction

A novel single‐step low‐temperature pyrolysis method is developed to efficiently remove encapsulated Ni nanoparticles (NPs, 10–50 nm) from both regular‐grade (<5 wt.% metal impurities) and industrial‐grade (<10 wt.% metal impurities) carbon nanotubes (CNTs). This approach eliminates the need for conventional multi‐step purification processes, which often involve high‐temperature corrosive gas oxidation and acid washing. The new strategy transforms and redistributes encapsulated Ni‐NPs into homogeneously sized nanoclusters (NCs, ≈1 nm) that are evenly dispersed on the surface of CNTs. Surface and bulk sensitive spectroscopic analyses reveal the predominant formation of Ni 3 N‐NCs, along with some metallic Ni‐NCs. The treated materials demonstrate exceptional electroactivity toward CO 2 reduction to CO, with the best‐performing CNT‐PTFE‐Mel‐650 sample achieving an ultra‐low onset overpotential of −19 mV and 98% CO selectivity in a current density range of 100–700 mA cm −2 . This NC catalyst demonstrates 25% lower voltage at 700 mA cm −2 compared to the single atom catalyst (SAC) control. Experimentally verified ab initio molecular dynamics (AIMD) models are simulated, and subsequent density functional theory (DFT) calculations further support the thermodynamic stability of Ni 3 N‐NCs and their favorability for CO 2 reduction. This work establishes a new method for creating ligand‐free electroactive NCs for efficient electrochemical reactions.