This work was jointly completed by University of Electronic Science and Technology of China, Canadian Light Source and Rice University. Professor Xia Chuan from College of Materials and Energy is the first author and correspondent, and Professor Haotian Wang from Rice University in the United States and Professor Hu Yongfeng from Canadian Light Source are the correspondent. The cooperative team has established a solid foundation in the field of electrocatalytic materials research and electrochemical reactor design, and achieved fruitful research results.
Transition metal monoatomic materials have high atom utilization rate, unique electronic structure and clear and adjustable coordination structure, which show excellent activity in various electrocatalytic processes. However, the low atomic density of metals in traditional monoatomic materials (usually less than 5 wt .% or 1 at). %) greatly limits its overall catalytic performance and industrial application prospect, so it is very important to develop a general synthesis strategy for transition metal monoatomic materials with high loading. The existing "top-down" and "bottom-up" processes have great limitations in improving the metal loading of synthesized monoatomic materials (Figure 1, a-b). Taking the single atom supported by carbon material as an example, the existing "top-down" method is to make defects on the surface of carbon material carrier, and then stabilize the single atom through the defects. However, because the defect size cannot be accurately controlled, the number of defect locations is very limited, and when the metal load increases, clusters are easily formed at large defect locations. The "bottom-up" method uses metal and organic precursors (such as metal-organic skeleton, metalloporphyrin molecules and metal-organic small molecules) to obtain carbon materials loaded with metal atoms. When the metal loading is too large, clusters or particles will be produced during pyrolysis because there is not enough isolation space between metal atoms.
In view of this, the team developed a preparation method of monoatomic catalytic materials (figure 1c) which is different from the existing "top-down" and "bottom-up" processes, so as to break through the limitation of monoatomic loading. The team innovatively used graphene quantum dots with large surface area and high thermal stability as carbon substrates, and modified them with -NH2 groups to make them have high coordination activity for metal ions. After introducing metal ions, a cross-linked network with metal ions as nodes and functionalized graphene quantum dots as structural units can be obtained, and finally highly loaded metal monoatomic materials can be obtained by pyrolysis. Compared with the traditional "top-down" and "bottom-up" monoatomic catalyst synthesis methods, the method reported in this study not only ensures the high dispersion of the initial anchoring time of high-content metal ions, but also effectively inhibits the agglomeration of metal atoms caused by substrate sintering and reconstruction in the subsequent pyrolysis process.
XAFS, HADDF-STEM and other characterization methods prove that the supported metal monoatomic catalytic materials prepared by this method can ensure the monodispersion of metal atoms and realize metal loading far beyond the level reported in the existing literature. With this method, the team successfully prepared an Ir monoatomic catalytic material with a mass fraction as high as 4 1.6% (with an atomic fraction of 3.84%) (Figure 2), which was several times higher than the maximum loading of Ir monoatomic reported in the literature.
In addition, the synthesis strategy is universal and can be used to prepare other noble metal or non-noble metal highly loaded metal monoatomic catalytic materials. For example, on carbon-based materials, the maximum loading of Pt atoms can reach 32.3 wt. %, and the average lifetime of nickel atoms can reach 65,438+05 wt.% (Figure 3).
Xia Chuan, a professor at the School of Materials and Energy, University of Electronic Science and Technology of China, is a national young talent. The research direction is electrocatalysis, electrosynthesis and electrochemical biosynthesis based on new energy, and it is devoted to realizing the energy and material cycle of carbon balance. In-depth and systematic research has been carried out in the characteristic direction of "on-site synthesis of liquid fuels and basic chemicals", and fruitful results have been achieved in the field of reactor and catalyst design. * * * Published more than 50 academic papers, authorized 3 American patents and cited more than 5,200 times. In the past five years, he has published more than 20 papers in high-level journals at home and abroad, such as Science and Nat, as the first author/correspondent. Energetic, Nat. Nat Qatar. Chemistry, etc. Among them, 9 papers are highly cited by ESI and 2 papers are hot topics.