Radical-Mediated Dynamic Reconstruction of Ni-N-C Single-Atom Catalysts for Wide-Potential CO₂-to-CO Electroreduction

Ni-N-C single-atom catalysts are widely regarded as highly selective electrocatalysts for CO₂ reduction to CO; however, the catalytically relevant Ni species under operating conditions remains unclear. Here we provide in situ evidence that Ni-N-C catalysts undergo radical-mediated dynamic reconstruction during CO₂ electroreduction, which affords >90% CO Faradaic efficiency during a broad potential window (-0.6 to -1.5 V vs RHE). In situ X-ray absorption spectroscopy together with quasi-in situ electron paramagnetic resonance spectroscopy reveal a radical-driven evolution pathway in which isolated Ni-N₄ sites progressively aggregate into metallic Ni clusters via hydrogen-radical-induced processes, followed by hydroxyl-radical-mediated oxidation to form NiO_x clusters; density functional theory calculations further support the key roles of these radicals in driving the transformation. Notably, the in situ-generated NiO_x clusters exhibit lower free-energy barriers for all elementary steps of CO₂-to-CO conversion than the initial Ni-N₄ sites. These results show that the sustained performance of Ni-N-C catalysts originates from radical-driven dynamic structural evolution rather than a static single-atom precursor, offering mechanistic insights into dynamic electrocatalysis for CO₂ reduction.