Research On Problems In Electrocatalytic Ammonia Synthesis Systems And The Application Of Metal-Free Based Doping In Electrocatalytic Ammonia Synthesis

Ammonia is one of the world’s most important energy sources and is used in a variety of applications including industry,agriculture,pharmaceuticals and energy storage.Currently,industrial ammonia synthesis mainly relies on the Haber-Bosch（HB）method,which has the drawbacks of massive energy consumption and raising greenhouse gas emissions.The mild,eco-friendly,renewable electricity-driven electrocatalytic conversion of nitrogen（N₂）to high-value ammonia（NH₃）is a promising alternative to the HB method for ammonia synthesis.However,extremely low solubility of N₂in aqueous solution,difficult activation of the nitrogen-nitrogen triple bond and competition from hydrogen evolution reactions all lead to unsatisfactory performance of electrochemical ammonia synthesis.At the same time,the ubiquitous plague of NH₃ contamination in electrochemical ammonia synthesis and various potential problems during the experimental process have also put it under question.This thesis focuses on the issues of the ENRR system and the modification of heteroatom doping to improve the performance of catalyst.The issues of ENRR system have been identified and overcome,and further improve this system.In addition,the performance of catalyst for ENRR was also improved by heteroatom doped.Details of the research are as follows:（1）The specific experiments indicated that when solutions containing chloride ions are used as electrolyte in the ENRR,the formation of chlorine gas（Cl₂）occurs at the anode during electrolysis,which in turn dissolves in water to form hypochlorous acid（HCl O）.In an H-type cell,the strongly oxidizing HCl O formed at the anode oxidizes the ammonium（NH₄⁺）generated from the cathode cell and diffused into the anode cell,and in a single port cell,the NH₄⁺generated is even completely oxidized.At the same time,the rate of Cl₂ precipitation from the anode accelerates with increasing applied voltage,and the associated oxidation of NH₄⁺also accelerates.This increases the difference of NH₄⁺concentration in the cathode and anode cells,which in turn increases the rate of diffusion of NH₄⁺from the cathode to the anode cell.This can have a significant impact on the quantitative and results analysis of NH₃produced in ENRR,leading to significant inaccuracies of the experimental results in ENRR.（2）A simple hydrothermal method was used to synthesize sulfur-doped samarium hydroxide（S-Sm（OH）₃）in one step,and the synergistic interaction between S and Sm（OH）₃ was used to obtaining efficient ENNR properties.The results of TPD demonstrate that S-Sm（OH）₃greatly increases the amount of N₂ adsorbed,XPS analysis shows a significant increase in oxygen vacancies.The highest ammonia yield(r _NH3)of 21.14μg h^-1 mg^-1_cat.and Faraday efficiency（FE）of 29.16%were achieved with 0.1 M Na₂SO₄ as the electrolyte,much higher than that of undoped Sm（OH）₃(r _NH3:10.02μg h^-1 mg^-1_cat.,FE:25.6%),and the performance was maintained after 55 h of electrolysis.This demonstrates that our catalysts can remain stable and unchanged for long periods of time.