Intrinsically Conductive π-d Conjugated Layers with Co-N₄ Active Sites for Efficient Nitrate Electrocatalysis and...

Electrochemical synthesis of ammonia from nitrate has been extensively investigated as a potential alternative to the energy-intensive Haber-Bosch process. This approach not only operates under ambient conditions but also simultaneously removes nitrate contaminants while producing ammonia as a value-added product. However, the ongoing quest lies in designing an efficient electrocatalyst that achieves a high ammonia yield rate, high selectivity, and long-term stability. Herein, we report the outstanding performance of a Co-N₄ coordinated π-d layered Co₃(HITP)₂ (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) in nitrate electrocatalysis. The unique combination of abundant Co-N₄ active sites and superior electrical conductivity enables significant electrocatalytic activity, delivering a maximum ammonia yield rate of 56.8 mg cm^-2 h^-1 at -0.8 V vs RHE and a Faradaic efficiency of ∼91% at -0.4 V vs RHE. Mechanistic analysis reveals that alkaline conditions accelerate water dissociation to generate adsorbed hydrogen intermediates (H*), which are utilized by Co-N₄ sites to drive the stepwise hydrogenation of nitrate to ammonia while suppressing competing hydrogen evolution reaction (HER) pathways. Furthermore, integration of this catalyst into a zinc-nitrate battery resulted in a maximum power density of 5.3 mW cm^-2 and an open-circuit potential of ∼1.45 V. These results highlight the potential of π-d conjugated Co-N₄ materials as an efficient catalyst for both environmental remediation and energy conversion.