Recently, Prof. Xingke Cai’s group from the Institute for Advanced Study at Shenzhen University published a research article titled “A Metal Coordination Number Determined Catalytic Performance in Manganese Borides for Ambient Electrolysis of Nitrogen to Ammonia” in the “Advanced Materials” on February 10, 2024. First author of the article is Dr. Muhammad Asim Mushtaq working as a postdoc fellow and Prof. X. Cai is a co-corresponding author with Prof. X. Sun from UESTC, Chengdu, Sichuan.
Ammonia (NH3) is a crucial compound and finds numerous applications in pharmaceuticals, synthetic fibers, and fertilizer manufacturing industries, as well as energy storage. It can also be used as a hydrogen energy carrier without carbon footprints, which is expected to have a significant influence on the future H2 energy economy. However, the conventional Haber–Bosch approach utilized to produce NH3 at elevated temperature (400–500°C) and pressure (200 bar) is energy consuming and environment pollutive. Alternative strategies to replace the Haber–Bosch process for NH3 production are highly desirable. Among all strategies, electrocatalytic nitrogen reduction reaction (NRR) in an ambient condition with water as the hydrogen source has been taken as the most promising technique, which can easily be compatible with agriculture, industry, and renewable energies.
In this work, a series of pure phase manganese boride (MnBx) materials, including Mn2B, MnB, MnB2, and MnB4 were successfully synthesized which show different coordination numbers for the Mn atoms. Through the structural characterization and performance comparison of these materials, we found that with the increase of B content in the compounds, the catalytic activity of a single Mn catalytic site is greatly improved. The optimal FE and ammonia production rate of MnB4 reached up to 38.5±2.7% and 74.9±2.1μgh−1mgcat−1 at−0.3V, respectively, much higher than the currently reported boride materials. This is because the number of B atoms coordinated with Mn atoms increases as the B/Mn ratio in the compound increases, resulting in an increase of valence electrons transferred from Mn to B. This increases the adsorption of N2 on Mn atoms and the intrinsic catalytic activity of Mn atoms for the hydrogenation of *N2. This coordination number modulation strategy provides a new solution for the development of high-performance transition-metal-boride-based NRR catalysts.
This work was supported by funding from the Natural Science Foundation of China (Grant Nos. 52373266, 52003163, and 22105129), the Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2022A1515010670 and 2022A1515011048), the Science and Technology Innovation Commission of Shenzhen (Grant Nos. KQTD20170810105439418 and 20200812112006001). Link to the article: https://doi.org/ 10.1002/adma.202313086
