Size‐Dependent Effect of Ni Nanoparticles Confined in Ni‐Modified Flower‐Like Carbon Toward CO ₂ Electroreduction Reaction

The Ni anchored nitrogen-doped carbon (Ni-N-C) are considered a promising catalysts toward electrocatalytic CO₂ reduction reaction (CO₂RR). During preparation process, the inevitable formation of Ni nanoparticles is generally considered unfavorable. However, emerging evidence suggests that the impact of Ni nanoparticles on CO₂RR is governed by confinement and structural evolution, which remains poorly understood and motivates systematic investigation. In this work, a flower-like carbon framework was designed to confine Ni species, enabling the coexistence of Ni-N-C sites and different sizes Ni nanoparticles. The results reveal that moderate Ni introduction (0.2-1 mmol) stabilizes small Ni nanoparticles and enhances micropore. Consequently, the Ni-N-C/Ni-0.2 and Ni-N-C/Ni-1 samples achieved superior CO₂RR activity, delivering a CO faradaic efficiency (FE_CO) of ∼90% at -1.0 V versus. RHE. Importantly, the confinement of flower-like carbon ensured that FE_CO could be retained above 85% even after 30 h continuous operation. Time-resolved structural characterizations combined with density functional theory calculations reveal that catalyst deactivation originates from the gradual transformation of confined Ni species into exposed metallic nanoparticles, which promote hydrogen evolution and hinder *COOH formation. This work establishes a direct correlation between Ni nanoparticle size evolution and CO₂RR performance, highlighting confinement engineering as an effective strategy for designing durable catalysts.