News Resource: Advanced Research Institute of

Multidisciplinary Science

Editor: News Agency of BIT

Translator: Han Miaomiao, News Agency of BIT

Single-atom catalysts (SACs), especially transition metal-nitrogen-carbon (TM-N-C) SACs with maximal atom utilization and tunable electronic structure have attracted extensive attention and have been rapidly developed and advanced in the past decade . Metal-organic frameworks (MOFs), due to their unique structural and compositional features, have emerged as one of the most prominent precursors for M-N-C-based ORR SACs. However, most of the MOFs-derived catalysts reported so far suffer from poor mass transfer at the three-phase interface, low intrinsic performance active centers, and low active center density. Therefore, directional design of the three-phase interface and active sites of MOFs catalytic materials is of great significance to improve the ORR catalytic performance of SACs.

Based on this, the team of Professor Wang Bo and Special Researcher Yang Wenxiu of BIT proposed a novel dual-template strategy to construct an atomically Co-doped three-dimensional cross-channel hierarchical carbon material (CoSA@NPC) as a high-performance ORR Electrocatalyst. DFT theoretical calculations show that the large number of carbon defects in CoSA@NPC modulates the adsorption of oxygen intermediates at the Co-N4 site during the ORR process, improving the catalytic efficiency of ORR; The optimized CoSA@NPC exhibited 7 times the electrochemical surface area and 11 times the intrinsic activity compared to the ice-templated (NI-NPC) catalyst. Furthermore, the assembled zinc-air batteries (ZABs) exhibit ultra-high specific capacity (905 mAh g-1) and excellent stability (350 h). The first author of this article is Li Liuhua, a master student of BIT.

Fig 1. Synthesis and Morphological Characterization of CoSA@NPC

a) Schematic diagram of the route for the synthesis of CoSA@NPC via a dual-template strategy. (b) SEM images and (c, d) TEM images show that the CoSA@NPC material exhibits a 3D trans-channel porous structure assembled from hollow spheres and hollow nanorod channels, which endow the material with a huge specific surface area and a Hierarchical pore size distribution effectively improves mass transfer during ORR. (e) The spherical aberration electron microscope clearly shows that the cobalt element in CoSA@NPC exists in the form of single atoms, and the corresponding EDX element map shows that the four elements Co, N, C, and O are uniformly distributed.

Fig 2. Structural Characterization of CoSA@NPC

XRD characterization shows that CoSA@NPC has only two distinct diffraction peaks of graphitic carbon, confirming the existence of Co as a single atom (Fig. 2a). Raman tests show that CoSA@NPC has larger ID/IG values compared to catalysts without silicon template (NS-NPC) or without ice template (NI-NPC), implying a greater degree of defects in the material (Fig. 2b). Oxygen adsorption tests confirmed that CoSA@NPC had stronger adsorption capacity for O2 molecules (Fig. 2b). The results of synchrotron radiation show that the Co element in CoSA@NPC is in an intermediate valence state between +2 and +3 valence, Co mainly coordinates with N, and there is no Co-Co bonding. The composite curves indicate that Co single atoms mainly exist in the configuration of Co-N4 (Fig. 2d-2f). The wavelet transformed images show that CoSA@NPC has completely different signal patterns from cobalt phthalocyanine and cobalt foil (Fig. 2g–2i).

Fig 3. Electrochemical performance of CoSA@NPC

Compared with NI-NPC, NS-NPC, and commercialized Pt/C materials, CoSA@NPC has better ORR performance, with a half-wave potential of 0.878 V, showing 7 times the electrochemical surface area and 11 times the electrochemical surface area. Intrinsic activity. Furthermore, the CV long-cycle and amperometric test results of CoSA@NPC demonstrate its excellent durability.

Fig 4. Battery performance and DFT calculations of CoSA@NPC single-atom catalysts

The Zn-air battery assembled with CoSA@NPC as cathode material exhibits an open-circuit voltage of 1.44 V, a maximum power density of 153.6 mW cm-2, and a specific capacity of 905 mAh g-1. It is worth mentioning that in the long-cycle test of charge-discharge Maintained the stability of 350h. DFT calculations show that the defects in CoSA@NPC effectively tune the electronic structure of the pure Co-N4 active site, greatly improving the adsorption of oxygen intermediates at the Co-N4 site and promoting the ORR activity.

Paper title：Atomically Co dispersed cross-channel hierarchical carbon-based electrocatalyst for high-performance oxygen reduction in Zn-Air battery

Paper link:https://pubs.rsc.org/en/content/articlelanding/2022/ta/d2ta05777h

Profile attached：

Wang Bo, member of the Standing Committee of the Party Committee of BIT, Vice President, Director of the Center for Frontier Science of High-Energy Matter，and Professor. The National Ten Thousand Talents Program Leading Talent, the winner of the National Outstanding Youth Fund, and the Young and Middle-aged Science and Technology Innovation Leading Talent of the Ministry of Science and Technology. Won the "Clarivate Analytics World Highly Cited Scientist", "Chinese Chemical Society Youth Chemistry Award", Beijing Youth May Fourth Medal and other honors. He is currently a member of the Standing Committee of the China Association for Science and Technology, a member of the Science and Technology Committee of the Ministry of Education; the executive director of the MOF Commission of the International IZA Society, an expert of the hydrogen energy special group of the Ministry of Science and Technology, the executive director of the Chinese Society for Environment and Sustainable Development, and the International Academy of Electrochemical Energy (IAOEES). Director, Vice Chairman of Zhongguancun Hydrogen Energy Technology Alliance, Director of Environment and Sustainable Development Society of China Ministry of Communications, part-time Director of Beijing-Tianjin-Hebei National Technology Innovation Center; He is the editorial board member of China Chemical Letters, Chinese Journal of Chemistry and Scientific Reports, and the deputy editor-in-chief of the Journal of Safety and Environment.. Mainly engaged in the theory and design of novel nanoporous materials, open framework polymers and their applications in key separation processes, environmental protection, and energy gas production and energy storage.

Yang Wenxiu is a doctoral supervisor and special researcher at the Institute of Frontier and Interdisciplinary Sciences of BIT. Mainly engaged in the synthesis of functionalized nanomaterials and their applications in the fields of catalysis and new energy (water electrolysis, zinc-air batteries, fuel cells and CO2 reduction, etc.). So far, 55 SCI papers have been published, among which, as the first/corresponding author, in Trend. Chem. (Cell sub-journal), J. Am. Chem. Soc., Angew. Chem. Int. Ed., Energy Environ. Sci. , ACS Energy Lett., and other internationally renowned journals published 25 papers, with a total of more than 3,000 citations. 6 invention patents have been applied for and 3 have been authorized. In addition, he presided over 2 National Natural Science Foundation of China projects, 1 postdoctoral fund, and 1 Beijing Institute of Technology start-up plan. He is a young editorial board member of Structural Chemistry and a guest editor of Batteries and Frontiers in Materials.

Research group website：https://bowang.bit.edu.cn/chinese/index.htm