Enhanced *COOH Adsorption over Edge-Rich Ni-N₄ Sites for Efficient Acidic CO₂ Electroreduction

Single-atom Ni catalysts hold great promise for the acidic CO₂ reduction reaction (CO₂RR), owing to their high CO selectivity. However, their performance under industrially relevant high current conditions is limited by the weak interaction between isolated Ni-N₄ sites and *COOH intermediates, restricting efficient CO₂ conversion. Here, we introduced edge-rich Ni-N₄ sites via support vacancy engineering to enhance *COOH adsorption, thereby boosting the CO₂RR activity and selectivity in acidic media. Density functional theory calculations revealed that edge-rich Ni-N₄ sites induced an upward shift in the Ni d-band center, leading to stronger *COOH binding and improved reaction kinetics. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images confirmed the uniform dispersion of single-atom Ni sites at the edge of the carbon support. X-ray adsorption spectroscopy further validated the successful anchoring of Ni-N₄ sites on the carbon nanotube matrix. Furthermore, in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy directly evidenced the enhanced *COOH binding on the engineered active sites. As a result, the optimized catalyst achieved a high CO faradaic efficiency exceeding 94.5% at 800 mA cm^-2, alongside a cathodic energy efficiency above 44.2% at pH = 1, suppressing previously reported benchmarks. This work establishes a versatile strategy for electronic structure modulation through edge-site engineering, offering a pathway to unlock the full potential of single-atom catalysts for the acidic CO₂RR at high current densities.