Reaserch On The Synthesis Of Fe-Mo Nanomaterials And Its Application In Nitrogen Fixation

Using water as a hydrogen source and electrochemically reducing N₂（NRR）to obtain NH₃ at ambinent condition is is regarded as the most promising alternative to the Haber-Bosch method.N₂ reduction is a slow and complex kinetic multi-step reaction.The difficulty lies in the need to break the nitrogen-nitrogen triple bond with a high activation barrier.How to rationally design and synthesize high-efficiency electrocatalysts to improve the ammonia production rate and Faraday efficiency（FE）of the electrochemical nitrogen fixation process is the current difficulty facing electrochemical nitrogen fixation.Fe-Mo-based nanomaterials show great application prospects in electrocatalysis due to the similar components and unique electronic structure of biological enzymes.However,there are few reports on Fe-Mo-based nanomaterials as NRR electrocatalysts.In this paper,the NRR catalytic performance of Fe-Mo-based nanoelectrocatalysts is discussed in detail,and the possible nitrogen fixation mechanism is predicted by density functional theory（DFT）,The specific research content is divided into the following three parts.（1）Design and synthesis of iron-grafted molybdenum oxide nanosheets（Fe@Mo O₃ NSs）NRR electrocatalyst.Some iron ions were grafted onto the molybdenum oxide nanosheets by dipping,and the materials were analyzed by detailed characterization methods.When the NRR performance test is performed in a neutral electrolyte（0.1 M Na₂SO₄）,the ammonia production rate can reach 9.66μgh^-1mg^-1_cat.at-0.6 V vs RHE,and the FE is 13.1%.（2）Fe₂（Mo O₄）₃ nanoparticle was designed and prepared by hydrothermal method,and then its structure and composition were characterized and analyzed in detail.Subsequently,the nitrogen fixation performance of Fe₂（Mo O₄）₃ nanoparticles was tested in detail and the results were analyzed.The ammonia production rate and FE in 0.1M Na₂SO₄ reached 18.16μg h^-1mg^-1_cat.and 9.1%,respectively.The ammonia production rate in 0.1 M HCl reached 20.09μg h^-1mg^-1cat.The performance and catalyst structure remained stable after the second cycle test.We have gone through a series of rigorous control experiments and found that its excellent electrocatalytic performance is mainly due to the synergistic effect of Fe³⁺and Mo O₄^2-.The theoretical calculation results prove that the NRR reaction path on the surface of Fe₂（Mo O₄）₃ nanoparticles（110）is a distant pathway.The potential barrier is 0.98 e V.（3）It is conjectured that the energy band of the semiconductor can be adjusted by doping with metal atoms to improve the performance of the catalyst.This conjecture is proved by theoretical calculations.The band gap of molybdenum oxide will decrease as the doping ratio of iron atoms continues to increase,and the oxygen vacancies introduced with the doping promote the adsorption capacity of nitrogen on the catalyst surface.The oxygen vacancies（OVs）introduced with the doping promote the adsorption capacity of nitrogen on the catalyst surface.This conjecture was verified through theoretical calculations,and it was found that the reaction barrier on the Fe doped Mo O₃nanosheets（001）surface was only 1.43 e V.After this,Fe doped Mo O₃ nanosheets were synthesis by hydrothermal method,and the actual NRR catalytic performance was tested in electrolytes with different p H values.The results show that there is excellent NRR catalytic performance in 0.1M Na₂SO₄,the rate of ammonia production reaches28.52μg h^-1 mg^-1_cat.,and the FE is 13.3%.The above experiments prove that Fe-Mo-based compounds have high catalytic activity and stability for NRR,which provides a good idea for improving the catalyst structure.