Directed Structural Evolution of Nickel Nanoparticles into Atomically Dispersed Sites for Efficient CO₂ Electroreduction.

Electrochemical CO₂ reduction (CO₂RR) to carbon monoxide (CO) offers a sustainable pathway for carbon utilization, yet challenges remain in terms of improving selectivity and activity. Herein, we report a Ni/NC catalyst synthesized via a milling - pyrolysis method, in which Ni particles anchored on nitrogen-doped carbon (NC) are electrochemically activated under an Ar atmosphere, leading to their structural evolution into single-atom Ni sites. After activation in Ar atmosphere, the current density nearly doubles (from ≈30 to ≈60 mA cm⁻²), and concurrently, the Faradaic efficiency of CO stays at ∼90% with the potential set to -0.8 V vs. RHE. Comprehensive characterizations, including X-ray photoelectron spectroscopy (XPS), aberration - corrected scanning transmission electron microscopy (AC - STEM), along with extended X - ray absorption fine structure (EXAFS), confirm the change of Ni particles into atomically dispersed Ni-N_x moieties during activation. Notably, in situ Raman spectroscopy identifies ^*COOH as the key intermediate, while electrochemical analyses reveal accelerated charge transfer and favorable kinetics for Ar-Ni/NC. Additionally, the catalyst shows great selectivity and stability over 24 hours of non - stop operation. This study emphasizes the dynamic change of Ni active sites under working conditions, offering useful ideas for designing transition metal catalysts for large - scale CO₂ to CO conversion.