Research On Design And Preparation Of Catalyst And Its Performance For Electrochemical Synthesis Of Ammonia

With the rapid growth of global demand and the vigorous development of society and economy,it’s particularly important to slove the problems of energy supply and environmental pollution.“Ammonia”is recognized as an ideal carrier of hydrogen energy and is expected to become a new generation of effient,clean and renewable energy carriers.Therefore,it is extremely urgent to develop new high-efficiency catalysts for electrochemical nitrogen reduction reactions.This thesis designed and synthesized SnS nanoflowers uniformly coated with a carbon layer and FeCo LDH with a hollow cube structure as an electrochemical nitrogen reduction catalyst.The catalytic activity of the catalyst was systematically studied and evaluated,and the catalyst was analyzed in depth in the electrochemical nitrogen reduction.The main research and results of the reaction mechanism in the reaction are as follows:1.SnS nanoflowers（SnS@C）uniformly coated with a carbon layer were synthesized by one-step hydrothermal self-assembly to enhance the activity of catalytic synthesis of ammonia at room temperature and piezoelectricity.Based on the structure of the hydrophobic carbon layer,the transfer rate of protons from the aqueous solution to the electrode surface is limited,the direct contact of N₂ molecules with the catalyst surface is realized,and the N₂ adsorption capacity and charge transport capacity of the catalyst surface are enhanced.Due to the synergistic effect of SnS and carbon layer,its eNRR performance is greatly improved.In 0.1M Na₂SO₄ electrolyte,SnS@C achieved an ammonia production rate of 7.95×10^-11mol·s^-1·cm^-2 and a Faraday efficiency of 14.56% at an overpotential of-0.5V vs.RHE.Demonstrates excellent catalytic selectivity and stability.In order to prove the reliability of the test results,This article has proved the reliability of the N source by designing adequate control experiments and ¹⁵N isotope labeling experiments,and ruled out the influence of all possible pollution on the experiment.This article has also systematically studied and proved the key role of the hydrophobic carbon layer in promoting the performance of eNRR.The DFT theoretical calculations show that the higher catalytic activity is attributed to the rearrangement of electrons between the SnS and the carbon layer interface,which greatly reduces the adsorption energy barrier of N₂ molecules on the111 crystal plane of SnS.Density of states calculation results show that the coverage of the carbon layer makes the edge of the conduction band of SnS produce defect energy levels,and further promotes the catalyst’s ability to activate N₂ molecules.2.Using Cu2O with cubic structure as a sacrificial template,FeCo LDH（FeCo LDH/HNCs）with a hollow cubic structure is prepared for electrochemical nitrogen reduction reaction.Using cubic Cu₂O as a template,FeCo LDH is grown on the outside,and then FeCo LDH/HNCs samples with hollow cubic structure are obtained by sacrificial template method.Based on the hollow cube structure of FeCo LDH/HNCs and the lamellar structure of LDH,it provides sufficient active sites for the electrochemical nitrogen reduction reaction.By adjusting the stoichiometric ratio of Fe and Co,it is revealed that metal elements can promote the electrochemical nitrogen reduction reaction.With 0.1M Na₂SO₄ as the electrolyte,FeCo_1/1 LDH/HNCs achieved an ammonia production rate of 21.73ug _NH3·h^-1·mg^-1_cat and a Faraday efficiency of 16.2%under the application of-0.5V vs.RHE potential,and confirmed that there is no side effect.The formation of the product N₂H₄ indicates that the catalyst has excellent eNRR catalytic activity and excellent selectivity.The experimental results also found that FeCo_1/1 LDH/HNCs exhibit higher reactive area and lower charge transfer resistance,so the optimal ammonia production rate and Faraday efficiency of FeCo_1/1 LDH/HNCs are higher than FeCo_1/2 LDH/HNCs and FeCo_1/3 LDH/HNCs.Through the evaluation of the eNRR performance of FeCo LDH/HNCs with different Fe/Co ratios,it is found that the ratio of metals in the bimetallic catalyst plays a key role in the sybergistic catalytic effect.And it is conclude that the catalytic performance is the best when the ratio of Fe/Co in the FeCo LDH/HNCs catalyst is 1:1.