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Breakthrough Made by Yin’s Team of BIT in Ammonia Synthesis under Wild Conditions

release date :2019-03-11 10:48:00  |   [ close window ]ViewCount:

    Translator: News Agency of BIT, Miao Yufei

    Editor: News Agency of BIT

   

  Recently, Yin Anxiang’s research group of School of Chemistry and Chemical Engineering in Beijing Institute of Technology and Key laboratory of atomic and molecular cluster science of Ministry of Education, cooperating with Yan Chunhua’s and Zhang Yawen’s research groups of Peking University, as well as Si Rui’s research group of Shanghai Synchrotron Radiation Light Source, has made a breakthrough in the field of ammonia synthesis by electrocatalysis of water phase at normal temperature and pressure. The research results titled "Promoting nitrogen electroreduction to ammonia with bismuth nanocrystals and potassium cations in water" was published on Nature Catalysis on 2019 March 4, which links to https://www.nature.com/articles/s41929-019-0241-7.

 

  The ammonia production industry plays a significant role in the development of society and national economy. At present, global ammonia production has exceeded 100 million tons per year, most of which is used for agricultural production to deal with food and shelter problem and the rest serves as important industrial raw material. In addition, ammonia has the advantages of high hydrogen content (up to 17.6% by mass ratio) and easy liquefaction, and is expected to become an important clean hydrogen storage and energy storage material with broad application prospects. However, since nitrogen molecules are too stable to activate, it is difficult to synthesize ammonia rapidly under mild conditions. The Haber - Bosch method are widely used in industry, applying high temperature (300-500 degrees Celsius) and high pressure (100-200 atm.) and other harsh conditions to help high purity hydrogen react with nitrogen on iron-based catalyst surface to produce ammonia. Both the energy and hydrogen come from fossil fuels (such as methane, etc.), displaying the disadvantages of high fuel consumption and high carbon dioxide emissions. The ammonia production industry consumes 3-5% of the world's annual methane and 1-2% of its energy supply, and produces 1.6% of the total carbon dioxide emissions. It has become an urgent scientific challenge to find suitable environment-friendly alternatives to realize high efficiency, low energy consumption and low emission ammonia synthesis under mild conditions.

 

  Nitrogen electroreduction (N2 + 3H2O →2NH3 + 1.5O2) provides a new pathway for the sustainable synthesis of ammonia. The reaction can be carried out under normal temperature and pressure, with massive accessible water and nitrogen (air) as the reaction raw materials and the electricity generated by sustainable energy (solar energy, wind energy, etc.) as the energy source, "zero-emission" ammonia synthesis thus can be achieved. Therefore, no matter serving as a potential alternative to the traditional Haber-Bosch method or as a crucial part of the new clean energy system, electrochemical ammonia synthesis technology has great potential of development and broad application prospects.

 

  However, the electrochemical ammonia synthesis technology still faces great challenges, and its development is severely bounded by the considerably low selectivity and activity of existing catalysts. The technique cannot be applied unless the selectivity and activity of catalysts can be significantly enhanced. Nevertheless, existing research experience and theories indicate that this kind of reaction catalysts generally face a severe "selectivity - activity" dilemma; that is on the one hand, catalysts with high theoretical activity usually lead to intensive side reactions of hydrogen evolution and thus lower the selectivity. On the other hand, the adsorption of nitrogen by the catalyst with high selectivity is too strong, leading to the difficulty of product desorption and low reactivity. Therefore, it is necessary to break through the existing theories and develop new catalysts and catalytic systems in order to make progress in the study of electrocatalytic ammonia synthesis and greatly improve both the selectivity and activity of catalysts.

Figure 1 Bi-K+ catalytic system realizing high efficient electrochemical ammonia synthesis: theoretical simulation, reaction model and catalytic performance

  Pioneering use of synergistic effect of non-noble metal catalysts (bi-nanometer catalysts) and alkali metal (potassium) cocatalyst, successfully enhances the adsorption and activation of nitrogen molecules on the surface of the catalyst, simultaneously inhibiting the side reaction of hydrogen evolution, which makes a break on the existing limit and substantially increase in electricity catalytic selectivity and the reaction rate of synthetic ammonia. At normal temperature and pressure (25 degrees Celsius, 1 atm.), starting from water and nitrogen, high selectivity (whose electron utilization rate is higher than 66%) and high rate of ammonia production (3.4 g NH3 g -- 1 h -- 1) can be achieved. This result is reported to be enormously improved in terms of quantity so far, which provides a possibility for the practical application of electrochemical synthesis of ammonia. It is worth mentioning that the catalytic system also possesses extensive applicability. Not only bismuth catalysts, but also a series of common catalysts (Pt, Au, etc.) can be applied to the promotion of alkali metals. In addition, the catalytic system can also function in the carbon dioxide electrocatalytic reduction reaction, being of significant importance for energy and environment. This study offers a new approach for the synthesis of ammonia with sustainable energy and high efficiency under mild conditions.

 

  The research was funded by the National Key Research and Development Program of China, the National Natural Science Foundation of China, Beijing Institute of Technology (BIT) and High-Performance Computing Platform of Peking University (PKU). Study Co-authors include Hu Changwen and Wang Bo research group from BIT. Researcher Sun Wei from PKU, professor Wang Guoxiong from Dalian Institute of Chemical Physical of Chinese Academy of Sciences and professor Zhou Zhiyou from Xiamen University have given strong support in the course of the study. Special researcher Yin Anxiang from BIT, Professor Zhang Yawen and Professor Yan Chunhua from PKU and researcher Si Rui of the Shanghai Synchrotron Radiation Facility are the co-corresponding authors of the research. The co-first authors are doctoral students Hao Yuchen from BIT and Guo Yu from PKU.

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