The Structure-property Relationship Of Non-Noble Metal-Nitrogen-Carbon Nanomaterials In Mimetic Enzyme Catalysis And Electrocatalysis

Non-noble metal-nitrogen-carbon?M-N-C?nanomaterials with low price and good stability have promising applications in energy storage and conversion,environmental protection and catalysis,medical diagnosis and detection.However,their further developments are restricted by the complex structure and uncertainty of active sites.Therefore,it is of great importance to elucidate the structure-property relationship,which is beneficial to regulate the structure of M-N-C nanomaterials based on different catalytical reactions.In this thesis,we aim to build the structure-performance relationship between M-N-C nanomaterials and different catalytic reactions.The metal center and coordination environment for M-N-C nanomaterials are rationally designed to improve their enzyme-like properties,electrocatalytic NRR and CO₂RR performance significantly.Our work will provide insight into precise construction of high performance catalysts at atomic scale.The specific research contents and conclusions are as follows:1.We study the structure-activity relationships between different M-N-C catalysts and enzyme-mimicking catalytic properties.The mechanism of the structure-dependent enzymatic activity is systematically investigated and elucidated from the perspective of different configurations of M-N_x models?x=0,3,4,and 5;M=Fe,Co,and Ni?.The Fe-N/C-CNT nanomaterial with Fe-N₃ units is developed as excellent oxidase mimics.The underlying catalytic mechanism is fully revealed by deeply exploring the possible reactive oxygen species?ROS?,catalytically active sites,and reaction pathways.This Fe-N₃-C oxidase mimic is further applied as a feasible colorimetric platform for glutathione detection.This study makes the in-depth study of the structure-activity relationship between M-N-C structures and enzyme-like catalytic activity,which provides a new idea for designing efficient nanozymes rationally.2.We study the structure-selectivity relationship between different Mo-N-C structures and enzyme-like properties.The structure of Mo-N₃-C possesses the highest adsorption energy and specificity for hydrogen peroxide by making comparations among a series of Mo-N-C structures with different nitrogen coordination numbers.Then we successfully fabricate the heterogeneous single atomic molybdenum catalyst?Mo-SAC?with built-in Mo-N₃ sites as a proof-of-concept paradigm that shows specific peroxidase-mimicking activities.Relying on the homogeneity of active sites,the fundamental peroxidase-like mechanism is revealed by Fenton-like reaction and homolytic path from the perspective of structural features and molecular orbital theory.This peroxidase-like single-atom nanozyme is successfully applied for selective and sensitive analysis of xanthine in the human urine samples.This strategy of unraveling the structure-selectivity relationship will provide a new thought-way to the rational design of single-atom nanozymes and make up the gap between the nanozymes and natural enzymes.3.We study the structure-activity relationship between the structure of Fe-N-C catalysts and the electrocatalytic nitrogen reduction reaction?NRR?.We design an Fe-N/C-CNTs catalyst with built-in Fe-N₃ active sites through theoretical prediction and experimental verification.The hierarchical porous architecture,large active surface area,positively charged surface,weak ferromagnetism,and strong nitrogen chemisorption of Fe-N/C-CNTs all facilitate enormous potential for the electrochemical NRR.This catalyst exhibits enhanced NRR activity with NH₃production(34.83?g·h^-1·mg^-1_cat.),faradaic efficiency?9.28%at-0.2 V vs RHE?,selectivity,and stability in 0.1 M KOH aqueous media under mild conditions.The results of block experiments and density functional theory both reveal that Fe-N₃species with high spin moment make a spontaneous chemisorption for N₂ molecules,which are primary catalytically active centers for the NRR.This work not only further expands the study for the structure-activity relationship between M-N-C nanomaterials and NRR,but also serves as a typical example of precisely designing catalysts for N₂ fixation.4.We study the structure-activity relationship between different Ni-N-C structures and the electrocatalytic carbon dioxide reduction reaction?CO₂RR?.We design an Ni@Ni-N-C electrocatalyst with dual sites of Ni-N₂ structure and Ni cluster encapsulated in the carbon layer,which is used to overcome the drawback for the limited amount and type of active sites in single-atom catalysts.This catalyst exhibits great CO₂RR performance to produce CO with low reaction overpotential,broad potential range,high CO Faraday efficiency and current density.The experimental results and DFT calculations reveal that the introduction of Ni cluster encapsulated in the carbon layer can adjust the local electron distribution on the surface of Ni@Ni-N-C catalysts,promote the interaction between COOH*group and Ni-N₂ sites,and reduce the energy barrier for reducing CO₂.This research makes a much deeper investigation for the structure-activity relationship between M-N-C nanomaterials and CO₂RR,which paves a new avenue for tuning the CO₂RR catalytic performance of M-N-C and single-atom catalysts precisely.