Themolysis Of Zirconium Metalloporphyrin MOFs To Single Atom Catalysts For Electrochemical Ammonia Synthesis

The production of ammonia from atmospheric nitrogen is of great significance to human life in the light of its huge demand in fertilizer production and pharmaceutical industry,as well as the potential to be a promising fuel.Generally,the industrial production of ammonia relies on the Haber-Bosch process,which requires huge consumption of resources.The electrocatalytic nitrogen reduction reaction proceeds under ambient conditions,thus holding great promise for ammonia synthesis.Nevertheless,the conpetitive hydrogen evolution severely restricts the amourtt of produced ammonia,which renders the large-scale application of electrocatalytic nitrogen unachievable.Therefore,it is imperative to synthesiae electrocatalysts featuring high performance of nitrogen reduction as well as the siuppression of hydrogen evolution.Single-atom catalysts(SACs)have been widely applied in diverse reactions.Besides,the well-defined active sites of single atoms make it convenient for mechanism studies.In the electrocatalytic nitrogen reduction reaction,SACs can effectively suppress the hydrogen evolution and the fully exposed active sites can promote the efficiency of nitrogen reduction.Featuring well-defined structure,large surface area high porosity and great functionality,metal-organic frameworks(MOFs)have been proven as ideal platform for the synthesis of SACs,The incorporation of porphyrin units into the ligands provides more binding sites for metal ions and endows MOFs with new functions.The construction of SACs derived from metalloporphyrin MOFs is not limited to the micropore confinement,thus faclitating mass transfer.Based on the above mentioned facts,this dissertation mainly concentrates on the following points:1.Thanks to the structural uniformity and synthetic tunability of PCN-222,a series of SACs with the identical microstructure,including Fei-N-C,Co1-N-C and Nii-N-C,have been successfully constructed and used as model electrocatalysts.In the electrochemical ammonia synthesis tests,Fe1-N-C exhibits superior activity to Coi-N-C and Nii-N-C counterparts,following the trend Fei-N-C>Coi-N-C>Nii-N-C.2.Based on the ideal model of single-atom catalysts,theoretical calculations have been conducted to unveil the intrinsic difference in these catalysts,revealing that Fei-N-C shows the lowest energy barrier of the rate-determining step during NRR process.Bader charge analysis indicates that Fei-N-C possesses the most positive charges,inhibiting the approach of protons and suppressing hydrogen evolution.