Basic Research On Energy Efficiency Improvement Strategy Of Electrocatalytic Nitrogen Reduction Synthesis Of Ammonia

Ammonia is an important chemical substance in industrial production and an ideal hydrogen storage medium.Nowadays,industrial ammonia production mainly relies on the Haber-Bosch process?N₂+3H₂=2NH₃?with high energy consumption and high carbon dioxide emissions.Therefore,in view of the increasing energy and environmental problems,it is urgent to develop alternative technologies for ammonia synthesis under mild conditions.Compared with the Haber-Bosch process,electrocatalytic nitrogen reduction?NRR,2N₂+6H₂O=4NH₃+3O₂?technology can realize the thermodynamic non-spontaneous process of directly synthesizing ammonia from water and air under mild conditions,and the reaction raw materials have a wide range of sources.Therefore,electrocatalytic nitrogen reduction technology has been recognized as a potential alternative technology for ammonia synthesis by Haber-Bosch process.However,due to the difficult activation of N?N bond,low solubility of nitrogen and strong competitive reaction of hydrogen evolution under mild conditions,electrocatalytic nitrogen reduction technology is facing two major challenges including low ammonia production rate and current efficiency.Therefore,based on the design of highly active nitrogen reduction catalyst and study for the inhibition of competitive reaction of hydrogen evolution,this paper systematically studied the strategy to improve the efficiency of electrocatalytic nitrogen reduction synthesis of ammonia through electrochemical test,ultraviolet spectrum analysis,nuclear magnetic analysis,isotope tracer analysis and gas chromatography.Research progress has been achived as follows:1. Based on the low ammonia production rate caused by the strategy of inhibiting hydrogen evolution,the mechanism of nitrogen reduction and hydrogenation process is studied by using materials with highly active hydrogen evolution.The importance and necessity of hydrogen activation in nitrogen reduction process are discussed,and the experimental and theoretical basis for the selection of electrocatalytic nitrogen reduction is provided.2. On the basis of verifying the importance and necessity of hydrogen activation,Mo₂C,a highly hydrogen-producing active material,is selected as the catalyst for electrocatalytic nitrogen reduction.As the specific surface area of Mo₂C increased by adjusting the size of the catalyst,more opportunities for N₂ diffusion are provided to the catalyst surface,effectively improving the rate and efficiency of the electrocatalytic nitrogen reduction.3. In view of Mo and Fe element are both the activity sites of the nitrogenase and based on the experimental basis of Mo₂C,Fe₃C nanodots embedded in carbon nanosheets is designed and applied the electrochemical nitrogen reduction at ambient conditions.The experimental results prove that Fe also has the ability of N₂ adsorption and activation,which provides a new choice for the development of efficient electrochemical nitrogen reduction catalysts.4. It is predicted by the theoretical calculation that binary-metal compounds possess more efficient nitrogen reduction activity than the single-metal compounds.Therefore,the binary-metal carbide Fe₃Mo₃C is scientifically designed and synthesized.The high efficiency catalytic potential of Fe₃Mo₃C in electrochemical nitrogen reduction is indicated by combining theoretical calculation with experiments.5. Based on the problems of extremely low solubility of N₂ and strong hydrogen evolution in the electrochemical ammonia synthesis system at ambient conditions,a pressurized electrocatalytic nitrogen reduction system at room temperature is designed and established for the first time to effectively improve the solubility of N₂ in solution and inhibit the hydrogen evolution reaction,and therefore,effectively reducing the application voltage and improving the Faradaic efficiency of the catalytic system.