Microenvironment regulation of M-N 4 single-atom catalysts (SACs) is a promising way to tune their catalytic properties toward the electrochemical CO 2 reduction reaction. However, strategies that can effectively introduce functional groups around the M-N 4 sites through strong covalent bonding and under mild reaction conditions are highly desired. Taking the hydrophilic Ni-N 4 SAC as a representative, we report herein a [2+1] cycloaddition reaction between Ni-N 4 and in situ generated difluorocarbene (F 2 C:), and enable the surface fluorocarbonation of Ni-N 4 , resulting in the formation of a super-hydrophobic Ni-N 4 -CF 2 catalyst. Meanwhile, the mild reaction conditions allow Ni-N 4 -CF 2 to inherit both the electronic and structural configuration of the Ni-N 4 sites from Ni-N 4 . Enhanced electrochemical CO 2 -to-CO Faradaic efficiency above 98 % is achieved in a wide operating potential window from -0.7 V to -1.3 V over Ni-N 4 -CF 2 . In situ spectroelectrochemical studies reveal that a highly hydrophobic microenvironment formed by the -CF 2 - 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.