Synthesis And Applications Of Metalloporphyrin Derived Two-dimensional Carbon Nanomaterials

Electrochemical oxygen reduction reaction?ORR?plays an important role in energy storage and conversion equipment,where electrocatalysts play a key role in improving the efficiency and performance of ORR energy storage devices.Metal,N-codoped carbon?M-N-C?nanostructures are promising electrocatalysts for replacing platinum-group-metal ones toward ORR or other gas-involved energy electrocatalysis.Metal organic framework?MOF?has been widely used to prepare M-N-C catalysts as precursors due to the ability to obtain an M-N-C catalyst with a porous structure and active metal center uniformly dispersed by pyrolysis.Also,as we know,2D carbon nanosheets are becoming an increasing hot spot due to the intrinsic advantages of continuous electron conduction pathways,easily film processing and large specific surface area,which can benefit greatly the conductivity as well as electron transfer in the electrochemical process.However,high-quality two-dimensional MOF nanostructures is difficult to synthesize rapidly at large-scale,it is still a challenge to prepare two-dimensional M-N-C nanostructures.In this paper,the surfactant-assisted method,supplemented by filtration,ultrasonic and microfluidic control,realized the controllable preparation of metal porphyrin two-dimensional nanocrystals,and synthesized two-dimensional M-N-C materials with its precursors.The two-dimensional M-N-C material with interconnected hierarchical porous structure was further fabricated by etching,and its ORR catalytic performance was studied.The specific research work is as follows:1.Using urfactant-assisted method,supplemented by filtration,sonication and microfluidic control,5,10,15,20-tetrakis?4-pyridyl?porphyrin?TPyP?acetic acid solution and copper acetate?Cu?Ac?₂?H₂O?aqueous solution was mixed to obtain monodisperse copper porphyrin two-dimensional nanocrystal and their aggregated cluster.The average thickness and lateral size of the obtained copper porphyrin two-dimensional nanocrystals are about 80-100 nm and 700-800 nm.The three-dimensional clusters are assembled from two-dimensional nanocrystals with an average diameter of 1.2-1.5?m.2.The Cu-N-C Nanodiscs?Cu@Cu-N-C?was obtained by pyrolysis the above monodisperse copper porphyrin two-dimensional nanocrystals,which maintained the morphology of copper porphyrin two-dimensional nanocrystals,and the average thickness is about 80 nm.Further analysis showed that Cu@Cu-N-C contains three elements of copper,nitrogen and carbon,of which copper exists in the form of single atoms copper and copper nanoclusters.The onset potentials of Cu@Cu-N-C catalyst is 0.88 V?vs.RHE?,and the current density is 5.7 mA cm^-2,and the catalytic performance is lower than that of the Pt/C catalyst.3.Based on the above Cu@Cu-N-C materials,the secondary level microstructure was prepared in the interior of Cu@Cu-N-C catalyst by chemical etching to obtain interconnected hierarchical porous topology Cu-N-C-ICHP catalyst with plant leaf stomata-like pore.Further analysis showed that Cu-N-C-ICHP consists of three elements of copper,nitrogen and carbon,of which copper exists in the form of single atoms copper.Cu-N-C-ICHP has a unique open ends hierarchical porous structure with a broad pore size distribution,and the mesoscale holes are running through the top to the bottom surfaces of the carbon-based matrix.The onset potential of Cu-N-C-ICHP catalyst is 0.97V?vs.RHE?,and the half-wave potential is 0.85 V?vs.RHE?.Compared with Cu@Cu-N-C,the catalytic performance of Cu-N-C-ICHP has been significantly improved,which is equivalent to Pt/C catalyst.The results show that the interconnected hierarchical porous structure gives carbon nanomaterials faster mass transfer efficiency,larger specific surface area and more active sites.The synergistic interactions between them play a critical role for boosting the ORR activity.