Tuning Active Hydrogen on Reconstructed RuO₂/Co(OH)₂ Catalysts for Selective Ammonia Synthesis.

Abstract

The electrochemical nitrate reduction reaction (eNO₃RR) 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 RuO₂/Co₃O₄ precatalyst and optimizing the electrolyte composition (OH^- and NO₃ ^- concentration), thereby selectively enhancing ammonia formation. Consequently, the in situ reconstructed RuO₂/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-NO₃ ^- 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 RuO₂ 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 eNO₃RR.