A Study On Electrochemical Synthesis Of Ammonia At Ambient Temperature And Pressure

Traditional Haber-Bosch process have many defects including high cost,high energy consumption and serious environmental pollution.And electrochemical ammonia synthesis has been regarded as a promising alternative to the present Haber-Bosch process for ammonia production,this is because the electrochemical method can overcome the thermodynamic limit of ammonia formation reversible reaction and can be operated at atmospheric pressure.And with the development of study for electrochemical ammonia synthesis,it is possible to achieve ammonia synthesis directly from air and water at room temperature and pressure in the future.In the field,the reaserch of solid proton conductor electrolyte system is the most widespread.In this paper,the electrochemical ammonia synthesis in a polymer electrolyte membrane is studied using Nafion membrane at ambient temperature and pressure.The performance of carbon paper loaded with Pt/C and blank carbon paper is studied using Nafion membranes in H⁺ or H⁺/NH₄⁺ form,respectively.The results show that ammonia can be produced on the two cathode at ambient temperature and pressure within the whole range of applied voltage from 0.2 V to 2.0 V.The produced ammonia is retained in the membrane using H⁺-form Nafion membrane as electrolyte.The yield of ammonia appears to be higher with the H⁺/NH₄⁺-form Nafion membrane both for the two cathode,suggesting the presence of NH₄⁺ in the membrane,facilitates the electrochemical reduction of nitrogen.The yield of ammonia on blank carbon paper electrode can be comparable with that for carbon paper loaded with Pt/C electrode,which implies that Pt/C is not a good electrocatalyst for N₂ reduction.The degradation rate of the Pt/C catalyst were studied,it was found that the activity of Pt/C will decrease after a period of time in a certain voltage,and the activity of Pt/C can recover under the higher voltage.To develop new catalysts for nitrogen electrochemical reduction,g-C₃N₄ catalyst is prepared by the thermal polycondensation process,and Pt/g-C₃N₄ catalyst is obtained by reducing Pt onto g-C₃N₄ nanosheets with ethylene glycol.The phase composition and morphology of the two kinds of catalysts are characterized by XRD,SEM,TEM and XPS.The performance of carbon paper loaded with Pt/g-C₃N₄,carbon paper loaded with g-C₃N₄,carbon paper loaded with Pt/C and blank carbon paper electrode is compared.It was found that the catalytic performance of Pt/g-C₃N₄ is greatly improved in spite that the performance of Pt/C is almost the same with blank carbon paper,which suggests that g-C₃N₄ carrior is in favor of nitrogen reduction reaction and inhibit hydrogen evolution reaction to some extent.The yield of ammonia appears to be higher with the H⁺/NH₄⁺-form Nafion membrane both for Pt/g-C₃N₄ and g-C₃N₄,further testing the role of NH₄⁺ in the membrane facilitating the electrochemical reduction of nitrogen.