Research On Controllable Preparation Of Carbon-supported Nano Non-noble Metal Oxides And Electrocatalytic Synthesis Of Ammonia

The electrocatalytic nitrogen reduction reaction（NRR）provides a green and sustainable new way to synthesize ammonia.However,the N≡N bond is activated difficultly under normal temperature and pressure.At the same time,the hydrogen evolution reaction（HER）usually compares with NRR,the development of catalysts with high-activity and high-selectivity for electrochemical ammonia synthesis has become one of the goals pursued by researchers.In this paper,glucose and sucrose are used as carbon sources to prepare carbon microspheres.The influence of hard template addition method and hard template method supplemented by soft template agent method on the microstructure of electrocatalysts and its performance of catalytic ammonia production are studied.On the basis of the iron-based electrocatalyst,the second metal M（M=La,Ni and Mo）is introduced to regulate the catalyst to improve its electrocatalytic ammonia production performance in the low-temperature molten salt system.Electrocatalysts are prepared by an impregnation method after carbon microspheres are synthesized using a hard template method.Electrocatalytic synthesis of ammonia is carried out in a molten salt electrolyte at 250°C.The results show that the way of adding the hard template has a great influence on the structure of the catalysts.The carbon microspheres prepared by adding the hard template during hydrothermal reaction have a microporous（2.32nm）structure with a specific surface area of 14.70 m²·g^-1.The surface of the obtained catalyst is dominated by Fe₂O₃ crystals,and a small amount of Fe₃O₄ crystals are induced at the same time.The carbon microspheres prepared with adding the hard template during carbonization are mainly mesoporous（5.23nm）structure with a specific surface area of 199.83 m²·g^-1,and Fe₂O₃ particles of 20～30nm are mainly uniformly supported on the surface of the catalyst.In addition,the type of carbon source basically has no effect on the structure of the catalyst.Electrochemical analysis shows that,compared with the method with of adding hard template agent during hydrothermal reaction,the method of adding hard template agent during carbonization changes the reduction path of Fe₂O₃ on the carbon microspheres.The obtained catalysts exhibit higher NRR activity due to improvement for inhibiting hydrogen evolution and enhancement of diffusion performence.the type of carbon source has a greater impact on the catalytic ammonia production performance.The catalyst prepared with glucose as the carbon source achieves a higher ammonia production rate and coulombic efficiency.The stability of the catalyst for ammonia synthesis is significantly improved with adding a hard template during hydrothermal reaction.The ammonia production rate and coulombic efficiency still remained respectively at 3.02×10^-9 mol·s^-1·cm^-2 and 21.55%after electrolysis for 12 hours.The method of adding hard template agent during carbonization can effectively improve the initial activity of the catalyst for ammonia production,and the ammonia production rate is as high as 1.48×10^-8mol·s^-1·cm^-2.On the basis of the hard template method,the microstructure and catalytic performance of the catalyst were further adjusted by introducing a soft template.The results showed that the introduction of polyvinylpyrrolidone and citric acid as soft templates can significantly change the pore size of the carbon microspheres.The pore size is increased to about 100 nm.However,the distribution and composition of the active components on the catalysts can not be changed with adding the soft templates of polyvinylpyrrolidone and citric acid.Adding hard template together with a soft template of polyvinylpyrrolidone under hydrothermal reaction significantly improves the stability of the catalyst.The ammonia production rate and coulombic efficiency are still 3.49×10^-9 mol·s^-1·cm^-2 and 22.18%,respectively,after electrolytic electrocatalytic reaction is continuously carried out for 12 hours.The catalyst prepared by adding citric acid during hydrothermal reaction and adding a hard template during carbonization exhibits a high initial ammonia production rate of 1.86×10^-8mol·s^-1·cm^-2.Based on the iron-based catalyst,second metals are introduced to adjust the ammonia production performance of the catalyst.The results show that the type of the second metals has a significant impact on the structure of the catalyst and the performance of catalytic ammonia production.The introduction of La significantly improves the selectivity of the catalyst.The introduction of Ni reduces the size of the carbon microspheres to about 1μm,and significantly changes the initial activity of the catalyst.The introduction of Mo reduces the size of the carbon microspheres to about 2μm,and significantly improving the stability of the catalyst.