[2+1] Cycloadditions Modulate the Hydrophobicity of Ni-N₄ Single-Atom Catalysts for Efficient CO₂ Electroreduction

Microenvironment regulation of M-N₄ single-atom catalysts (SACs) is a promising way to tune their catalytic properties toward the electrochemical CO₂ reduction reaction. However, strategies that can effectively introduce functional groups around the M-N₄ sites through strong covalent bonding and under mild reaction conditions are highly desired. Taking the hydrophilic Ni-N₄ SAC as a representative, we report herein a [2+1] cycloaddition reaction between Ni-N₄ and in situ generated difluorocarbene (F₂C:), and enable the surface fluorocarbonation of Ni-N₄, resulting in the formation of a super-hydrophobic Ni-N₄-CF₂ catalyst. Meanwhile, the mild reaction conditions allow Ni-N₄-CF₂ to inherit both the electronic and structural configuration of the Ni-N₄ sites from Ni-N₄. Enhanced electrochemical CO₂-to-CO Faradaic efficiency above 98 % is achieved in a wide operating potential window from -0.7 V to -1.3 V over Ni-N₄-CF₂. In situ spectroelectrochemical studies reveal that a highly hydrophobic microenvironment formed by the -CF₂- group repels asymmetric H-bonded water at the electrified interface, inhibiting the hydrogen evolution reaction and promoting CO production. This work highlights the advantages of [2+1] cycloaddition reactions on the covalent modification of N-doped carbon-supported catalysts.