Unravelling the Ru-promoted dynamic evolution of Cobalt hydroxide during nitrate reduction towards ammonia production

Geen ammonia synthesis through electrochemical nitrate reduction (e-NO3R) using cost-effective Co-based catalysts is promising, but the inevitable structural evolution induced by reductive potentials compromises long-term stability and hinders practical implementation. Focusing on β-Co(OH)2, which serves as the active phase in e-NO3R systems, this work combines experimental analysis and computational studies to reveal a dynamic surface *OH evolution process: *OH cleavage under negative potentials and *OH generation by the dissociation of NO3-. Notably, Ru nanoparticles anchored on β-Co(OH)2 nanosheets promote structural evolution by facilitating *OH cleavage and generation, thereby sustaining a highly active and selective OH-terminated surface. Simultaneously, Ru provides moderate *H adsorption, accelerates the conversions from NO3− to NO2− and from NO2− to NH3, and thus enhances ammonia synthesis. The optimized Co(OH)2-Ru catalyst achieves an ammonia yield of 98 ± 0.91 mg·h-1·cm-2 with a Faradaic efficiency (FE) of 97.7 ± 0.90 % at −0.7 V versus reversible hydrogen electrode (vs. RHE), while maintaining NH3 FEs above 95% across a broad potential window. This work elucidates structural evolution dynamics, offering a design principle for robust electrocatalysts. The unclear structural evolution mechanism of Cobalt-based materials restricts the long-term applications of nitrate reduction for ammonia synthesis. Here, the authors report a Ru-promoted dynamic evolution of cobalt hydroxides that can stably produce ammonia at high current densities.