Universal Formation of Single Atoms from Molten Salt for Facilitating Selective CO₂ Reduction

Clarifying the formation mechanism of single-atom sites guides the design of emerging single-atom catalysts (SACs) and facilitates the identification of the active sites at atomic scale. Herein, a molten-salt atomization strategy is developed for synthesizing zinc (Zn) SACs with temperature universality from 400 to 1000/1100 °C and an evolved coordination from Zn-N₂Cl₂ to Zn-N₄. The electrochemical tests and in situ attenuated total reflectance-surface-enhanced infrared absorption spectroscopy confirm that the Zn-N₄ atomic sites are active for electrochemical carbon dioxide (CO₂) conversion to carbon monoxide (CO). In a strongly acidic medium (0.2 m K₂SO₄, pH = 1), the Zn SAC formed at 1000 °C (Zn₁NC) containing Zn-N₄ sites enables highly selective CO₂ electroreduction to CO, with nearly 100% selectivity toward CO product in a wide current density range of 100-600 mA cm^-2. During a 50 h continuous electrolysis at the industrial current density of 200 mA cm^-2, Zn₁NC achieves Faradaic efficiencies greater than 95% for CO product. The work presents a temperature-universal formation of single-atom sites, which provides a novel platform for unraveling the active sites in Zn SACs for CO₂ electroreduction and extends the synthesis of SACs with controllable coordination sites.