Multi‐Dimensional Ni@TiN/CNT Heterostructure with Tandem Catalysis for Efficient Electrochemical Nitrite Reduction to Ammonia

Abstract Electrochemical nitrite reduction reaction (NO 2 RR) is considered a sustainable ammonia (NH 3 ) synthesis strategy. However, there are still significant challenges in designing efficient NO 2 RR catalysts. Here, carbon nanotube (CNT)‐encapsulated Ni nanoparticles (NPs) loaded on MXene‐derived TiN (Ni@TiN/CNT) heterostructure is constructed by combining molten salt etching strategy and chemical vapor deposition. Ni@TiN/CNT exhibits an excellent NH 3 yield rate (15.6 mg h −1 mg cat. −1 ), Faradaic efficiency (95.6%), and record cycle stability (NO 2 RR performance is virtually unattenuated after 60 cycles) at −0.7 V versus reversible hydrogen electrode (versus RHE). In addition, the Zn‐nitrite battery with Ni@TiN/CNT as the cathode shows high power density (9.6 mW cm −2 ) and NH 3 synthesis performance. Combining validation experiments and density functional theory calculations reveals that Ni@TiN/CNT follows the tandem catalytic mechanism. The TiN site preferentially adsorbs and activates NO 2 − , while the Ni site provides abundant active hydrogen for the subsequent reduction process. Meanwhile, the chainmail structure of CNT prevents the oxidation and leaching of active sites, thereby significantly enhancing the stability of Ni@TiN/CNT. This work provides a new inspiration for the preparation of durable and efficient NO 2 RR electrocatalysts with tandem catalytic sites.