Tuning Active Hydrogen on Reconstructed RuO 2 /Co(OH) 2 Catalysts for Selective Ammonia Synthesis

Abstract The electrochemical nitrate reduction reaction (eNO 3 RR) is widely recognized as a promising strategy for sustainable ammonia production and supporting the nitrogen cycle. However, its advancement is impeded by complex behavior of reaction intermediates and the inevitable reconstruction of precatalysts. To address these challenges, the generation and utilization of active hydrogen (*H) are strategically managed by tailoring the RuO 2 /Co 3 O 4 precatalyst and optimizing the electrolyte composition (OH − and NO 3 − concentration), thereby selectively enhancing ammonia formation. Consequently, the in situ reconstructed RuO 2 /Co(OH) 2 catalyst achieves an impressive ammonia yield of 35.9 ± 0.9 mg h −1 cm −2 and a Faradaic efficiency (FE) of 98.1 ± 2.6% at −0.3 V versus RHE. Furthermore, the catalyst shows significant potential for applications in nitrate‐rich wastewater treatment and rechargeable Zn‐NO 3 − batteries, maintaining stable operation for over 260 hours at 1 mA cm −2 with only a 6 mV increase in the potential window. Mechanistic studies reveal that electron‐rich RuO 2 facilitates *H generation through water dissociation, which subsequently migrates to Co(OH) 2 to hydrogenate nitrogenous intermediates, selectively producing ammonia. This study highlights the importance of designing efficient catalytic systems that address both precatalyst reconstruction and the complexities of reactant and intermediate conversion in electrolytes, which are essential for managing the intricate electron and proton transfer processes involved in eNO 3 RR.