Study On Preparation And Performance Of Electrochemical Ammonia Synthesis Catalyst

Ammonia production occupies a pivotal position in the national economy.Nearly 80%of ammonia is used for fertilizer production.The successful development of the synthetic ammonia industry not only solves the food problem caused by population expansion,but also promotes the development of related industries.In addition,ammonia has also received attention as a hydrogen storage and energy storage material.However,since N₂ is very stable and difficult to activate,it is difficult to obtain a fast reaction for ammonia synthesis.The traditional Haber-Bosch ammonia synthesis process currently used in industry must be carried out under severe conditions of high temperature（300～500°C）and high pressure（200～300atm）,which not only consumes a lot of fossil energy,but also emits immeasurable carbon dioxide,had a huge impact on the environment.With the increasing demand for ammonia,the global annual output of ammonia has exceeded 100 million tons and is increasing year by year.However,energy and environmental problems caused by the ancient Haber-Bosch process for ammonia synthesis have become increasingly prominent.Therefore,exploring an ammonia synthesis method with high efficiency,low energy consumption and environment-friendliness has become an inevitable requirement of social development.In recent years,the electrochemical N₂ reduction reaction（NRR）to synthesize ammonia has attracted the attention of the majority of researchers.It is a method with mature mechanism and the greatest hope among various new methods of synthesizing ammonia.The electrochemical synthesis of ammonia has obvious advantages.It can overcome the thermodynamic constraints of traditional ammonia synthesis and is carried out at room temperature and pressure.However,the slow kinetic process of NRR hinders the electrochemical generation efficiency of NH₃.In addition,the competitive hydrogen evolution reaction（HER）significantly reduces the Faraday efficiency（FE）of electrochemical ammonia synthesis.Therefore,while suppressing HER,it is very desirable to synthesize an effective electrocatalyst to accelerate NRR.In this paper,graphene oxide（GO）and defective graphene oxide（DGO）were successfully prepared by the improved Hummers method,and then reduced to different forms of graphene（Graphene）by high temperature,which was used as a substrate,respectively,doped or loaded with transition metals,And finally got three different composite materials.In this experiment,potassium hydroxide（KOH）and high-purity nitrogen（N₂）were used as raw materials,and the experiment of electrochemical synthesis of ammonia was carried out under normal temperature and pressure.The catalytic performance of composite materials of three-dimensional defective graphene doped with iron（3D-DG/Fe）,three-dimensional defective graphene doped with iron and molybdenum bimetal（3D-DG/Fe Mo）,and defective graphene foam loaded with iron single atoms（DGF/Fe）were studied,and explored the influence of different catalyst morphology and the performance of electrochemical ammonia synthesis.The 3D-DG/Fe Mo catalyst can be seen from the element map that the successful doping of Fe and Mo elements,compared with the3D-DG/Fe catalyst,the measured ammonia yield rate is 24.1μg·h^-1·mg^-1_cat,Higher than 16.3μg·h^-1·mg^-1_cat of 3D-DG/Fe catalyst,and shows better stability.The DGF/Fe catalytic material was synthesized by microwave radiation and hydrothermal reaction method,and the successful preparation of DGF and Fe single atom was proved by HAADF-STEM and other characterization methods for aberration correction of the composite material.The electrochemical ammonia synthesis test showed that the ammonia yield was as high as 31.6μg·h^-1·mg^-1_cat.Based on the above findings,it is found that graphene-based metal single atoms are a promising catalytic material,and Fe single atoms can significantly enhance the activity of electrocatalytic ammonia synthesis.