Electrochemical Synthesis Of Nano-metal Oxides And Research On The Performance Of Electrocatalytic Nitrogen Fixation

Ammonia(NH₃)is one of the most important chemicals in the world with applications in agriculture,industry and energy carriers.The traditional method of NH₃production adopts the Harber-Bosch process,which is carried out under high temperature and high pressure,consumes a lot of energy and is accompanied by a large amount of greenhouse gas emissions.Electrochemical nitrogen reduction to synthesize NH₃ is driven by electrical energy at room temperature and pressure,and the process is simple,safe and controllable,which is considered to be a promising method to replace the Harber-Bosch process.However,the low NH₃ production rate and Faradaic efficiency(Faraday Efficiency,FE)of this process limit its large-scale industrial application.Designing and developing electrocatalyst with excellent activity and stability is the core of the current field of electrocatalytic nitrogen fixation.Nano-metal oxides(Nano Metal Oxides,NMOs)have unique surface electronic structures and are easy to control its surface defects,possessing broad application prospects in the field of electrocatalysis.Based on this,in this work,based on the electrochemical oxidation corrosion method,a series of NMOs containing oxygen vacancies(Oxygen Vacancy,V_O)were designed and prepared,and the preparation process was optimized to realize the regulation of V_O.The electrocatalytic nitrogen fixation performance of the synthesized NMOs was studied in detail,the effect of V_O on the catalytic activity was analyzed;the specific nitrogen fixation mechanism was discussed in combination with density functional theory(Density Functional Theory,DFT)calculations.The control of the catalytic performance of the material is realized from the perspective of defect engineering.The main research contents and experimental results are as follows:(1)Nano Fe₃O₄ materials were prepared by electrochemical oxidation and corrosion in sodium chloride electrolyte.Structural and compositional analysis found that V_O was introduced during the preparation.The electrocatalytic nitrogen fixation performance was tested.In 0.1 M Na₂SO₄,the NH₃ production rate was 12.09?g·h^-1·mg^-1_cat.,and the FE was 16.9%.After five cycles and 24 h long-term test,there is no obvious degradation in performance.No by-product hydrazine is produced in the process,showing good selectivity.Theoretical calculations indicate that the Fe₃O₄ catalytic ammonia production proceeds along alternate paths.(2)The electrochemical synthesis process was optimized,and three groups of Sn O₂nanomaterials with V_O concentrations of 13.4%,23.97%and 34.56%were designed and prepared successfully,which were compared with commercial Sn O₂.The electrocatalytic nitrogen fixation test results show that the higher the V_O concentration,the higher the activity and the better the ammonia production performance;the nano Sn O₂ with the highest V_O concentration obtains the NH₃ production rate and FE of 25.27?g·h^-1·mg^-1_cat.and 11.48%,showing better stability and selectivity.A series of test analysis showed that the higher the V_O concentration in Sn O₂,the larger the specific surface area,the more surface active sites,the stronger the charge transfer ability,and the more efficient electrocatalytic NRR performance.Theoretical calculations explore the mechanism by which V_O promotes the catalytic activity of Sn O₂,and the catalysis mainly proceeds along an alternate pathway.(3)Three groups of ternary oxide Bi OCl nanomaterials with different V_Oconcentrations were designed and prepared by the electrochemical oxidation corrosion method.The electrocatalytic nitrogen fixation performance in 0.1 M Na₂SO₄ shows that Bi OCl with the higher V_O concentration has better catalytic performance,the ammonia production rate reaches 19.01?g·h^-1·mg^-1_cat.,and the FE is 11.43%;it has better selectivity and stability.The more V_O in Bi OCL,the more reactive sites,and the better catalytic performance.