Ru single-atom catalysts achieved a record-high yield rate for NH3 production in N2 electrochemical reduction

Recently, the research group of Prof. Jie Zeng cooperated with Prof. Rui Si from Shanghai Institute of Applied Physics has made a breakthrough in NH₃ production from electrochemical reduction of N₂ by using Ru single-atom distributed on nitrogen-doped carbon (Ru SAs/N-C) as electrocatalysts. Ru SAs/N-C possessed a record-high yield rate for NH₃ production toward N₂ electrochemical reduction. This work was published on Advanced Materials (Adv. Mater. 2018, 30, 1803498) entitled as “Achieving a Record-High Yield Rate of 120.9 μg_NH3 mg^-1_cat. h^-1 for N₂ Electrochemical Reduction over Ru Single-atom Catalysts”. Dr. Zhigang Geng and graduate student Yan Liu were the co-first authors of this work.

Nitrogen is nutritionally unavailable due to the highly stable N≡N covalent triple bond. As such, high pressure and temperature (150-350 atm, 350-550 ^oC) are required to convert N₂ to NH₃ through Haber-Bosch process in industry. The harsh condition of Haber-Bosch process results in 1-2% of the world’s annual energy supply consumption. Moreover, the NH₃ synthesis through Haber-Bosch process requires hydrogen gas as source, which is generated from the steam reforming of natural gas with a large concomitant emission of CO₂. In view of the fossil fuels shortage and global climate change, it is highly desired to explore a catalytic process that produces NH₃ under ambient conditions. As a strategy of NH₃ synthesis under the ambient reaction condition, electrochemical reduction of N₂ into NH₃ has attracted particular attention. However, to date, the highest NH₃ yield rate among the reported electrocatalysts was only 23.8 μg_NH3 mg^-1_cat. h^-1 towards N₂ electrochemical reduction. Therefore, the development of highly active electrocatalysts for NH₃ production is desirable but remains challenging.

Herein, researchers prepared Ru SAs/N-C via pyrolyzing the Ru-containing derivative of zeolitic imidazolate frameworks (ZIF-8) which achieved record-high activity towards N₂ electrochemical reduction. At -0.2 V vs reversible hydrogen electrode, Ru SAs/N-C exhibited a Faradaic efficiency of 29.6% for NH₃ production with partial current density of -0.13 mA cm^-2. Notably, the yield rate of Ru SAs/N-C reached 120.9 μg_NH3 mg^-1_cat. h^-1, which was one order of magnitude higher than the highest value ever reported. Experimental result and theoretical calculation study further revealed that Ru SAs/N-C promoted N₂ dissociation, thereby resulting in enhanced activity. This work provides a guideline for the generation of atomically dispersed uniform single atomic materials and paves a new avenue for further research in the application of single atomic catalysts towards N₂ electrochemical reduction.

This work was supported by CAS, MOST of China, National Natural Science Foundation of China, and Anhui Provincial Key Scientific and Technological Project.

Source: https://onlinelibrary.wiley.com/doi/epdf/10.1002/adma.201803498