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.