Preparation And Electrocatalytic Properties For Ammonia Synthesis Of WO₃ And FeMoO₄

Ammonia(NH3)is an essential raw material in the chemical industry,and is expected to play a huge role in hydrogen and energy storage.The traditional Haber-Bosch method for ammonia synthesis requires high-temperature and high-pressure conditions,and has the problems of high energy consumption,large pollution and unbalanced distribution areas.In contrast,electrocatalytic N2 reduction reaction(NRR)is a green and economic ammonia synthesis process that uses electricity to catalyze the reaction of N2 and H2O under mild conditions.At present,electrocatalytic NRR has the problems of low yield,complicated detection process,and harsh experimental environment requirements.Therefore,it is necessary to optimize the experimental process,improve the detection standards and find the appropriate catalyst.In recent years,transition metal oxides have excelled in the field of electrocatalytic NRR,which has the advantages of easy availability of raw materials,simple synthesis,stability and high eff-iciency.On this basis,how to expand the types of transition metal oxides and further improve the catalytic performance of materials has also become a research hotspot in this field.Therefore,two transition metal oxide catalysts of tungsten trioxide(WO3)and ferrous molybdate(FeMoO4)were designed and synthesized in this paper,and their electrocatalytic NRR performance and related catalytic mechanism were studied.On the one hand,the nanowire WO3 material was prepared by a one-step hydrothermal method.The nanowires were interwoven to form a network-like pore structure,which was conducive to the adsorption and activation of nitrogen.The electro-catalytic NRR performance at different voltages was tested,and the NH3 yield and Faraday efficiency(FE)of WO3 showed a trend of increasing first and then decreasing with increasing voltage.Among them,at a voltage of-0.5 V vs.RHE,the NH3 yield reached a maximum of 11.31 μg·h-1.mg-1cat.,and the corresponding FE is 5.79%.In addition,in the 12-hour long-term test,the current density-time curve remained stable,showing excellent stability of the WO3 sample.Therefore,nano-WO3 material is a NRR catalyst with low cost,high catalytic activity and good stability.On the other hand,nanorod-shaped FeMoO4 materials were prepared by solvothermal method.Due to the advantages of Mo-Fe interaction,the average NH3 yield of the catalyst reached 16.01 μg·h-1·mg-1cat.at a voltage of-0.6 V vs.RHE,and the FE was 8.24%.Tests have shown that FeMoO4 material also has excellent stability.The source of NH3 was investigated by a series of control experiments,and false positive interference was excluded.The possible catalytic activity centers and reaction mechanisms of FeMoO4 materials were also investigated by density functional theory calculations.Studies have shown that Fe atoms are the active center for the adsorption and activation of N2,and the reaction mainly proceeds through alternate association paths with lower free energy barriers.Therefore,nano-FeMoO4 material is a very promising electrocatalytic NRR material.