Transmission Electron Microscopy Studies On The Sixth Main-Group Element Compounds In The Field Of Energy And Catalysis

Electrochemical energy storage is one of the key supporting technologies for large-scale grid incorporation of clean energy in the future.It not only helps to increase the flexibility and overall utilization of the power grid,but also promotes the extensive application of various transportation and electronic products.In electrochemical energy storage systems,zinc-air batteries and reaction cells for producing hydrogen/carbon-based fuels have high research value and broad application prospects.They achieve energy storage and conversion through specific electrocatalytic reactions,where the electrocatalysts play an indispensable role.Although noble metal-based catalysts have good electrocatalytic reactivity,they are expensive and have poor durability.If electrocatalytic energy storage technology completely relies on earth-scarce precious metal elements,it will be detrimental to the widespread popularity of clean energy in the future.How to develop environmentally friendly,efficient,low-cost,and durable non-precious metal-based catalysts is still an important frontier issue in scientific research.Before embarking on a detailed description of the research work,this paper first introduced the development history,basic structure,and working principle of the transmission electron microscopy research method.The origin,improvement,and current status of the transmission electron microscope were briefly described.From the perspective of the electron beam,sample,signal,etc.,the transmission electron microscope was divided into five major systems whose structures and principles were presented separately.In the application section,in addition to introducing three basic application modes of diffraction,imaging,and spectroscopy,the in-situ mode,as a renascent comprehensive characterization method in the time dimension,was also considered.New opportunities and challenges brought about by the in-situ mode for the future development of transmission electron microscopy were discussed.The research objects of this paper were mainly the compounds of the sixth main-group elements,involving oxides,sulfides,and selenides.According to the periodic sequence of the three elements O,S,and Se,the research works on Fe-doped Co₃O₄nanosheets,two-dimensional layered MoS₂,and MoSe₂/NiSe composite nanowires were introduced successively.Electrochemical tests demonstrated that these active materials were good candidates for the high-efficiency non-noble metal-based electrocatalysts.Among them,Fe-doped Co₃O₄ nanosheets had dual functionality in oxygen evolution/reduction reaction;MoSe₂/NiSe composite nanowires had synergistic effects in hydrogen evolution reaction;nitrogen-carbon materials compounded MoS₂ had a high selectivity in the carbon dioxide reduction reaction.They all showed good electrocatalytic activity and stability when they were respectively used as electrode active materials for zinc-air batteries and electrolysis reaction cells for hydrogen production and carbon dioxide reduction.In order to understand the design principles behind the material modification strategies and to explore the‘structure-property'relationship between the macroscopic properties of the materials and their microstructure,this paper studied the structural and chemical characteristics of these transition metal compounds by using transmission electron microscopy as the main research method and combining various other characterization methods.The doping effect of Fe element in Co₃O₄ nanosheets was analyzed;the induction effect of the NiSe core on the outer 1T phase MoSe₂ was discussed from the perspective of interfacial structure and electron transfer;the growth mechanism of the curled MoS₂ in nitrogen-carbon-based composites was verified by in-situ observation at the atomic scale.Besides,this paper also observed the arrangement of Mo atoms in the monolayer 1T'MoS₂,the defect state of the S atoms in the monolayer 2H MoS₂,and the structural features of the vertical double-layer 1T'/2H MoS₂ heterojunction and horizontal single-layer 2H MoS₂ homojunction.Based on the observed evolution characteristics of the point defects in the monolayer 2H MoS₂,a self-healing reaction mechanism that induced by chemical additives was proposed as well.Transmission electron microscopy showed unique advantages in observing the morphology and composite structure of the materials,evaluating the type and crystallinity of the phases,identifying the type and valence of the elements,determining the type and number of defects,analyzing the details of the interfacial structures,and tracking the structural evolution behaviors.Transmission electron microscopy plays an important role in promoting the development of high-efficiency electrocatalyst active materials in the field of energy and catalysis,as it not only helps to deepen the understanding of the‘structure-property'relationship,but also provides a useful reference for formulating new material modification strategies.