Stability and Redispersion of Ni Nanoparticles Supported on N-Doped Carbons for the CO2 Electrochemical Reduction

N-doped carbon systems constitute a unique platform for the isolation of metal atoms that have been proposed as active species in the electrocatalytic CO₂ reduction reaction (eCO₂RR). Among them the Nickel Nitrogen Carbon (NiNC) single-atom catalyst exhibits the highest efficiency for producing CO, at different potentials. The variation in the material synthesis produces defects with coordinatively saturated and unsaturated N-doped cavities, and once the metal is placed there these single atoms can present different metal oxidation states depending on the cavity nature. Synthetic protocols to produce single atoms from metal nanoparticles have been put forward, then the so-synthetized materials are complex as contain a variety of metal environments. Thus, although many studies have been devoted to NiNC materials, there are still discussions on the true nature of the active sites and particularly their coordination environment. In the present work, we have computationally evaluated experimental activity and selectivity of a wide potentially active sites for the single atoms and nanoparticles, where the optimal reactivity is found for N-doped models. The second aspect addressed here concerns the electrochemical stability of the reconstruction and redispersion of supported nanoparticles. At high CO coverages, Ni nanoparticles reconstruct by forming Ni(CO)₄ species that can redisperse on the host into active single atoms. In summary, the complexity of these metal-doped carbon systems needs to be considered holistically to understand their real electrocatalytic behavior.