Molecularly engineered covalent hydrophobic interface for enhanced CO₂ electromethanation in strong acid

Electrochemical conversion of CO₂ to methane provides a sustainable pathway for fuel synthesis, yet it inherently struggles to balance carbon utilization efficiency with product selectivity. Conventional surface engineering based on physical hydrophobic coatings often leads to interfacial instability and diminished charge transfer efficiency. To address these issues, we develop a cysteine-coated copper coordination complex catalyst modified with covalently bonded fluoroalkyl silane (FAS), allowing precise control over surface wettability. A breakthrough in highly acidic electrolytes is demonstrated, achieving a methane Faradaic efficiency of up to 66.2% at 400 mA cm^-2 (pH 1.8), alongside a single-pass carbon conversion efficiency of 31.1%, surpassing conventional alkaline-system benchmarks. Surface-enhanced Raman spectroscopy reveals a key *COOH intermediate for CO₂ activation, while in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy monitors the sequential hydrogenation pathway through *CHO and *CH₂O. Molecular dynamics simulations further reveal a distinct water exclusion zone near the catalyst surface, which arises from the hydrophobic covalent interface induced by the FAS coating. This interfacial engineering strategy suppresses the hydrogen evolution reaction by blocking water access, preserves hydrophobicity during operation, and offers a scalable path to improve the kinetics and selectivity of CO₂ electroreduction.