Electrochemical Synthesis Of Ammonia Directly From Water And Nitrogen At Atmospheric Pressure

With the rapid economic development,the demand for ammonia by humans is increasing.However,the traditional Haber-Bosch process has the problems of high energy consumption,high pollution and low single-pass conversion.The research on the new ammonia synthesis method is imperative.The electric field can break the thermodynamic limit of ammonia synthesis,and it can achieve directly atmospheric pressure electrochemical synthesis of ammonia from water and nitrogen.It has broad prospects for development.In this paper,Fe?NO₃?₃·9H₂O was used as precursor,activated carbon was used as carrier,and Fe₂O₃/AC catalyst was successfully prepared by impregnation method.Electrochemical synthesis of ammonia was studied at atmospheric pressure using molten NaOH-KOH as an electrolyte and water and nitrogen as raw materials using TEM,SEM,TG/DTA and XRD.The mechanism of electrochemical ammonia synthesis from water and nitrogen in molten NaOH-KOH suspensions of suspended Fe₂O₃/AC was investegated using thermodynamic analysis and TG/DTA,XRD and CV.It was found that Fe₂O₃/AC can be stably suspended in molten NaOH-KOH electrolytes.Fe₂O₃/AC catalysts can inhibit hydrogen reduction and enhance reduction of iron.The preparation conditions of Fe₂O₃/AC catalyst were optimized.The effects of catalyst loading,immersion time and calcination temperature on the performance of ammonia synthesis were investigated.The results showed that the electrochemical performance of Fe₂O₃/AC catalysts for electrochemical synthesis of ammonia was better under the conditions of calcination temperature of 300°C,carrier particle size of 200-300 mesh,loading capacity of Fe/AC=7/50 and impregnation time of 24 h.The influences of electrolysis voltage,carrier gas aeration method,cathode material and two-step ammonia synthesis process on the performance of synthetic ammonia were investigated.The results showed that the ammonia production rate can reach 8.27×10^-99 mol·s^-1·cm^-2with an applied voltage of 1.55 V in one-step ammonia synthesis process.and Coulomb efficiency is up to 13.7%at 1.15 V.The results indicated that the performance of ammonia synthesis can well be improved using graphite plate alloy cathode.The dispersion of feed gas is conducive to electrochemical synthesis of ammonia.In order to increase and the performance of electrochemical ammonia synthesis,the crystallinity of Fe₂O₃ was improved using activated carbon modified with liquid-phase oxidation.The results showed that the Coulomb efficiency and ammonia production rate of ammonia were respectively 32.3%and 8.57×10^-9mol·s^-1·cm^-2at 250°C and 1.15 V in ammonia synthesis process when Fe₂O₃/AC catalyst was prepared using activated carbon modified with 30wt%H₂O₂ and 9mol/L HNO₃ as carrier.Two-step method improve significantly the performance of synthetic ammonia.Coulomb efficiency is up to 79.8%at1.15 V,and the ammonia production rate is as high as 1.34×10^-8mol·s^-1·cm^-2at 1.75 V.