Fabrication Of Mo-based Catalysts And Their Performance In Electrochemical Reduction Of Nitrogen

The Haber-Bosch process,a significant invention was firstly developed in 1910 s,and Fe/Ru-based catalyst was applied to convert nitrogen and hydrogen to ammonia at 400-500 °C.At such a high temperature,the ammonia synthesis was slow owing to the unfavorable situation of reaction equilibrium.To avoid the disadvantage,pressures of 200-300 atmospheres was added to shift the equilibrium towards ammonia production.For operating the process at such an exacting condition,the energy input was 485 k J·mol-1.The industry of ammonia production synthesis over 500 million tons of NH3 per year,80% of it was put into fertilizer,consume 3-5% natural gas supply and about 2% energy consumed among the world.An energy-saving method would be highly desirable.Electrochemical reduction of N2 to NH3/NH4+ as a new method,contains a series of advantages.It could operate at ambient conditions by uncomplicated equipment from abundant N2 and water on the planet,and the electric energy could come from the sun and wind.This paper focuses on the active Mo electro-catalyst and prepared four different oriented Mo thin film catalysts by electro surfaces treatment methods.SEM,XRD,XPS and EDS were used to characterize materials surface geometry structure,crystal structure and electric structure.The ammonia was measured using UV-VIS spectrometer,the activity of the catalysts was estimated by Faraday efficiency,current density,ammonia synthesis rate.The results indicated that different crystal plane oriented Mo catalysts have different N2 reduction activity.Mo(110)plane is benefit for N2 reduction,Mo(211)plane is unfavorable for N2 reduction.The Mo-based catalysts have a low onset potential,and it starts ammonia produce at-0.29 Vvs.RHE.The maximum ammonia synthesis rate was 3.09×10–11 mol·s–1·cm–2,the maximum faraday efficiency was 0.72%.The Mo catalyst has a great stability,it can reduction of N2 to NH3 without decay of reaction rate about 9 h.The NH3 synthesis rate amplify as temperature raised,but it’s not suitable for faradaic efficiency.We using ionic liquid and ethylene glycol as solvent for different viscosity,(NH4)6Mo7O24 as Mo resource,Na BH4 as reduction reagent,prepared three kind of particle size Mo nano-catalysts.TEM,XRD,XPS and EDS were used to characterize materials surface geometry structure,crystal structure and electric structure.Mo catalyst synthesis from ionic liquid was about 1.5~1.8 nm and 2.8~3.4nm,and that from ethylene glycol was about 8~10 nm.All of them are easily oxidized and could be well loaded on activated carbon.The 1.5~1.8 nm Mo has the best activity,on which the maximum mass activity 27 ug·h-1·mg-1cat.and maximum faradaic efficiency 2.1% were been gotten.The ATR-IR was used to characterize the reaction intermediate,and the peaks of –NH2 bending and N-N stretching were clearly been detected.The peak of –Nx Hy enhanced with overpotential increasing,the peak of H2 O was contrary to that.We also founded that Li+ in the electrolyte is unfavorable for N2 reduction.Besides,we synthesized nano-sheet Ni Mo alloy and spongy porous Fe Mo alloy by self-growth on Ni and Fe through hydrothermal method,founded both of them are not active enough for N2 reduction,so it indicated that addition of Ni and Fe is harmful for N2 reduction compared to pure Mo.