Experimental Preparation And Theoretical Study Of Molybdenum-based Electrocatalytic Nitrogen Reduction Materials

Ammonia?NH₃?is regarded as an important chemical substance,which is widely used in agriculture,medicine and industry.Fertilizers,pharmaceuticals,resins,dyes,explosives and other products that are closely related to human life are all produced with NH₃.Considering the increasingly severe energy crisis and global warming,the industrial Haber-Bosch method with great amount of energy consumption needs to be improved.The electrochemical synthesis of ammonia can be carried out under ambient conditions,with the helps of some excellent catalysts.Moreover by adjusting the working potential,electrolyte and pH value,the NRR process can be effectively improved.Therefore,it is essential to seek electrocatalysts with higher NH₃ yield rate and Faradaic efficiency?FE?,good stability and excellent selectivity.In this work,hollow spherical Bi₂MoO₆ catalytic materials were synthesized by the one-step hydrothermal reaction.Such electrocatalyst affords a large NH₃ yield of 20.46?g h^-1 mg^-1_cat.and a high Faradaic efficiency of 8.17%at-0.6 V vs.reversible hydrogen electrode in 0.1 M HCl.Tests show that the material has good durability and selectivity as an effective electrocatalyst for NRR.This study will provide a significant low-cost and environmentally friendly electrocatalyst for the synthetic synthesis of NH₃.On the other hand,it will open up a promising direction for exploring Mo-based heterogeneous electrocatalysts.An in-depth understanding about the NRR mechanisms on the Bi₂MoO₆?131?surface was revealed by the Density Functional Theory?DFT?.The catalytic active sites and corresponding electronic structure changes on the Bi₂MoO₆ surface were analyzed at an atomic scale to further understand the origin of NRR catalyst activity.According to the theoretical calculation results,the oxygen vacancies V₁ and V₃ on the Bi₂MoO₆?131?surface can effectively activate the N₂ molecule.The optimal path follows the alternating mechanism at the active site of V₃.The reaction process from*NH₂ to*NH₃is the rate-determining step with a relatively low energy barrier of 0.693eV,which is conductive to NRR.With its unique electronic properties,TiO₂ is widely used in many fields such as photovoltaic cells,catalysis,optical devices,charge storage,antibacterial applications and so on.However,the pure TiO₂ has a low activity as an NRR electrocatalyst.We explored the changes of electronic and electrochemical properties of the rutile TiO₂?110?surface after Mo doping through the DFT calculations.The reaction mechanism of Mo-TiO₂ as a NRR catalyst was studied too.When the Mo is doped into the Mo₁ site,a hybrid state formed by the hybridization of Mo-4d and Ti-3d orbitals appears at about0.4 eV below the Fermi level.With the doping of Mo atoms,the adsorption ability of surrounding Ti atoms to N₂ is enhanced.The optimal NRR path is an alternate path at Ti₁ site,and its rate-determining step is 0.956 eV.The calculation results indicate that Mo doping can effectively improve the NRR catalytic activity of TiO₂.