Covalently Hydrophobic Nanocarbon Supported Ni Single-Atom Catalysts for Highly Selective CO₂ Electroreduction

Precise tailoring of hydrophobic microenvironments surrounding catalytic active sites has emerged as a critical strategy for enhancing the efficiency of electrochemical CO₂ reduction reaction. However, covalent modulation of catalyst hydrophobicity is rarely reported, and the mechanistic influence of hydrophobicity-driven interfacial catalysis remains unclear. Herein, we report a general synthetic methodology for the covalent immobilization of structurally tunable hydrophobic alkyl chains onto nanocarbon-loaded single-atom catalysts. The covalently hydrophobic nanocarbon supported Ni single-atom catalysts deliver near-unity CO selectivity over a broad potential range from -0.5 to -1.2 V (versus the reversible hydrogen electrode) in flow cells. Integrated spectroscopic, computational kinetic, and thermodynamic analyses reveal that the alkyl chains form hydrophobic barriers by disrupting interfacial water networks, resulting in a 0.37 eV increase in energy barrier of the hydrogen evolution reaction. The hydrophobic micro-environment further stabilizes the *COOH intermediate under aqueous conditions, lowering its formation Gibbs energy (ΔG) by 0.17 eV relative to unmodified catalysts. This work establishes a universal hydrophobic modification strategy for carbon-based catalysts that breaks the conventional activity-selectivity trade-off in aqueous electrocatalysis, opening new opportunities for optimizing gas-consumption electrochemical reactions.