The Preparation Of Modified Sillenite Bismuth Ferrite For Electrocatalytic Nitrogen Fixation

Ammonia has a wide range of applications in industry,agriculture,clean energy and other fields,as a result,nitrogen fixation technology plays an important role in various fields.The current widely used artificial nitrogen fixation technology is the Haber-Bosch method,but due to its harsh reaction conditions,this method consumes a large amount of energy and produces a large amount of greenhouse gas,which will aggravate the global greenhouse effect.Therefore,scientists begin to explore sustainable nitrogen fixation systemst can be achieved under ambient conditions.Among them,electrocatalytic nitrogen reduction reaction is a new type of nitrogen fixation technology converting nitrogen into ammonia with electrocatalysts in a certain voltage.The reaction process has the potential to utilize clean without secondary pollution and is expected to alleviate the environmental problems caused by the Haber-Bosch nitrogen fixation method.The electrocatalyst plays a decisive role in the efficiency of electrocatalytic nitrogen fixation,but the rate of ammonia production and selectivity of traditional electrocatalysts are not very ideal,so it is necessary to develop an electrocatalyst with high nitrogen fixation activity and selectivity.Sillenite bismuth ferrite(Bi₂₅FeO₄₀)with a body-centered cubic structure has unique photorefractive,piezoelectric,electro-optical,and photo-conductive properties.It has a large number of oxygen vacancies and the potential for electrocatalytic nitrogen fixation.In this paper,Bi₂₅FeO₄₀is modified by two methods:Bi_1.8Fe_1.2Sb O₇/Bi₂₅FeO₄₀composite electrocatalyst（BFSO/BFO）and Nb-doped Bi₂₅FeO₄₀（Nb/BFO）electrocatalyst are prepared and studied.In order to determine its activity and stability of electrocatalytic nitrogen fixation,the main contents and conclusions are as follows:（1）BFSO/BFO is obtained by one-step hydrothermal method,and the compounding ratio can be changed by adjusting the molar ratio of Bi/Sb added.The results show that the formation of Bi_1.8Fe_1.2Sb O₇pyrochlore leads to the amorphization of the composite electrocatalyst,increasing the oxygen vacancy density and the specific surface area of the catalyst,which provides more adsorption and reaction sites for the nitrogen fixation reaction.At the same time,the presence of Bi_1.8Fe_1.2Sb O₇reduces the electrochemical impedance of the catalyst and increases the electrochemically active surface area and the current density significantly at the same potential.Among them,0.8:1:0.2 BFSO/BFO not only has the best electrocatalytic nitrogen fixation effect at-0.2 V vs.RHE,which is 2.2 times as high as Bi₂₅FeO₄₀,but also has good electrocatalytic stability.（2）Nb/BFO is obtained by one-step hydrothermal method.The research results show that Nb replaces the site of Fe in the BFO partially with the doping of Nb,so that part of Bi³⁺in BFO is converted to Bi⁵⁺,resulting in the change of Nb⁵⁺to the oxidation state of Nb⁺³,while the valence state of Fe³⁺is unchanged.The doping of Nb effectively improves the electron transfer rate,reduces the electrochemical impedance of the catalyst,and increases the current density on the catalyst surface at the same potential.Electrocatalytic nitrogen fixation results show that Nb/BFO with different ratio shows the best electrocatalytic nitrogen fixation activity at-0.3 V vs.RHE,of which 1-Nb/BFO（the doping amount of Nb is 1 mmol）has the highest ammonia production rate,which is 1.9 times as high as Bi₂₅FeO₄₀.What’s more,1-Nb/BFO performs excellent electrocatalytic stability,maintaining a good activity after reused five times.