Research On Design And Preparation Of Iron-based Catalysts And Their Performance For Electrocatalytic Synthesis Of Ammonia

The raw materials for electrocatalytic ammonia synthesis are cheap and readily available water and nitrogen,which can be used to synthesize ammonia without carbon emission under normal temperature and pressure,with great potential for development.However,the electrocatalytic nitrogen reduction process of ammonia production will be subject to competition from the decomposition of hydrogen produced by electrolyzed water,resulting in a significant reduction in the selectivity of catalytic ammonia production.Designing and developing new high-activity,high-selectivity catalysts is an urgent task for electrocatalytic ammonia synthesis.In this paper,carbon microspheres?CMSs?are prepared using glucose as the carbon source by a hydrothermal method.Followed by using CMS as the carrier,and Fe?NO₃?₃·9H₂O is used as the iron source to prepare the CMS supported iron-based electrocatalysts.The catalysts are characterized by using XRD,SEM,TEM and XPS.The catalytic performances are improved via regulating the microstructure of catalysts.The results show that the addition of Fe³⁺to the glucose solution during hydrothermal synthesis can significantly improve the yield of carbon spheres.The prepared carbon spheres exhibit standard spherical spheres with a uniform diameter of about 10?m.The iron oxides supported on the prepared Fe₂O₃/CMS electrocatalyst are mainly Fe₂O₃ with a small amount of Fe₃O₄ nanocrystals,which the particle size is about 30?40 nm.The addition amount of iron during hydrothermal synthesis,the carbonization temperature,the loaded amount of impregnated iron,and calcination temperature are the main factors affecting the ratio of Fe₂O₃ to Fe₃O₄.The ratio of Fe₃O₄ to Fe₂O₃ on the Fe₂O₃/CMS electrocatalyst will cause different catalytic ammonia production performance.The catalysts have excellent electrocatalytic ammonia synthesis performance when prepared by adding a small amount of iron during hydrothermal synthesis,at a relatively high carbonization temperature,with an appropriate amount of iron impregnation load,and at a relatively mild calcination temperature.As the electrolysis voltage increases,the ammonia production rate increases,whereas the ammonia production coulombic efficiency decreases.The results also show that the catalysts exhibit higher catalytic performance in the early stage of the reaction,and the catalytic activity and selectivity gradually decrease as the reactions progress,but remain at a relatively high level after 12 hours.The highest ammonia production rate of Fe₂O₃/CMS electrocatalyst at normal pressure and 250?is 1.77×10^-8mol·s^-1·cm^-2,and the highest Coulomb efficiency is 82.6%.Based on Fe₂O₃/CMS,a second metal component was introduced to prepare Fe-Ni/CMS and Fe-Mo/CMS bimetallic catalysts,respectively.The diameter of the Fe-Ni/CMS catalyst is about 3?m and the active component is Ni Fe₂O₄.The diameter of Fe-Mo/CMS catalyst is 10?m,and the active components are Fe Mo O₄ and Fe₂O₃.The bimetallic catalysts have a certain ammonia production rate and coulombic efficiency for electrochemical ammonia synthesis,and the catalyst stability has been significantly improved.The CMS-supported iron-based catalyst prepared in this paper has unique advantages of easy preparation,low cost of raw materials,and excellent electrocatalytic ammonia production performance.It should provide theoretical support and guidance for the development of efficient electrochemical ammonia synthesis under mild conditions.