Galvanic Replacement of Au on Co(OH)2 Nanoneedle Arrays: Breaking the 90% Faradaic Efficiency Barrier for Electrochemical Nitrogen Reduction and Ambient Ammonia Synthesis

The electrochemical nitrogen reduction reaction (ENRR) is an environmentally friendly and sustainable route for ammonia (NH3) production. It offers a promising alternative to the energy-intensive Haber–Bosch process, significantly reducing its environmental impact. In this study, cobalt hydroxide nanoneedle arrays were successfully prepared on nickel foam (Co(OH)2@NF) by a facile hydrothermal approach. The Co(OH)2 structure was then overlayered simply by Au atoms through galvanic replacement. This process created a synergistic effect between Co and Au, which promotes N2 activation while suppressing the competing hydrogen evolution reaction (HER). Density functional theory (DFT) calculations revealed that Au incorporation significantly modifies the electron density redistribution around adsorbed N2 molecules, creating more favorable sites for protonation and thereby enhancing the ENRR kinetics. The replacement of Co with Au atoms increased the Faradaic efficiency (FE) from 38.2 ± 2.4% to 90.1 ± 2.3%. The NH3 yield rate (rNH3) nearly doubled from 0.45 µg h−1 cm−2 ± 0.02 (2.00 × 10−8 mol h−1 cm−2) at –0.15 V vs RHE to 0.85 ± 0.06 µg h−1 cm−2 (4.98 × 10−8 mol h−1 cm−2) at a more favorable potential of + 0.00 V vs RHE. The Co(OH)2–Au@NF electrocatalyst can be used as a stable and effective electrocatalyst for the green synthesis of NH3, which is, to the best of our knowledge, among the highest FE values reported for ENRR under ambient conditions, particularly considering the extremely low overpotential.