Professor Xiang Zhonghua from Beijing University of Chemical Technology: non carbonated covalent organic polymer materials for catalytic oxygen reduction

One of the key to break through the bottleneck of fuel cell industry is to develop high-efficiency, stable and low-cost redox catalyst In recent years, metal organic framework materials (MOFs) / covalent organic framework materials (COFS) have been widely used as precursors for the preparation of electrocatalysts, but the subsequent high-temperature carbonization will lead to the change or even destruction of the structure of MOFs / COFS, making them lose the original highly ordered and adjustable structural advantage Covalent organic polymers (COP) have good hydrothermal stability, high specific surface area, structural diversity and adjustability, and gradually play an important role in the field of electrocatalysis Recently, Beijing University of chemical technology has made new breakthroughs in this research field with Professor Zhonghua's research group (angel Chem Int ed doi: 10.1002/anie.201808226) Brief introduction to the research group of Professor Xiang Zhonghua molecular energy materials research and development center of Beijing University of Chemical Technology (Xiang Zhonghua research group) was established in July 2014 At present, the center has 1 Professor, 1 associate professor, 1 postdoctoral teacher and 1 research assistant It mainly focuses on the development of easily tailored and highly stable covalent organic polymer materials (COP), focusing on the function oriented design of materials structure at the molecular level for the application in the field of energy (j.am.chem.soc., 2015, 137, 13301; adv.mater., 2016, 28, 6253; angel.chem Int ed.; 2011, 50, 491) and engineering preparation (zl201510674580.7) Typical achievements include cop in fuel cell cathode Oxygen Reduction Catalysis (angel Chem Int ed., 2014, 53, 2433; adv mater., 2014, 26, 3315; ACS Nano, 2017, 11, 8379; ACS energy lett., 2017, 2, 1308; J energy chem., 2017, 26, 1168), nano energy, 2017, 35, 115; chem Eng SCI., 2017, 162, 33; SCI Bulletin, 2018, 63, 369), zinc air (liquid flow) battery (nano energy, 2018, 47, 361), etc Postdoctoral recruitment: due to the needs of research work, the research team plans to recruit a postdoctoral: 1 Application conditions 1 People with research background of porous material preparation, electrocatalysis, photocatalysis, etc., who have published more than two high-level SCI papers in relevant journals 2 In principle, the fresh doctoral graduates shall not be more than 35 years old, and the doctors with working experience shall not be more than 40 years old 3 With international vision and team spirit, strong interest in scientific research, and the ability to independently carry out scientific research 4 Physical and mental health, practical working attitude, able to assist in daily laboratory management and postgraduate training 2、 Relevant treatment 1 Salary and welfare: salary and welfare shall be implemented in accordance with the relevant provisions of the national postdoctoral program and the relevant provisions of Beijing University of chemical technology 2 Social insurance benefits: Postdoctoral students shall participate in social insurance and pay housing fund according to relevant regulations during their stay in the station 3 Medical treatment: the postdoc transferred from the archives relationship to our university can enjoy the medical treatment at public expense according to the official staff standard of our university 4 Other treatment: postdoctors join the school labor union and participate in the activities of the labor union during their stay in the station; the scientific research achievements obtained during their stay in the station are treated the same as the teachers of the school, and can be rewarded according to the relevant provisions of the school's Institute of science and technology development Please send your resume to: xingzh@mail.buct.edu.cn Brief introduction to Zhonghua Professor Xiang Zhonghua, Professor of School of chemical engineering, Beijing University of chemical technology, doctoral supervisor, director of research and development center of molecular energy materials In 2013, he obtained a Ph.D degree in chemical engineering and technology from Beijing University of chemical technology, and in 2013-2014, he worked in Kent Hale Smith Prof Liming Dai Laboratory of Department of macromolecular engineering and science of Case Western Reserve University in the United States for postdoctoral research In 2013, it won the first prize of natural science of the Ministry of Education (ranking second); in 2017, it won the 9th "Hou Debang chemical science and technology award Youth Award"; in 2017, it was rated as "Excellent Communist Party member of Beijing University"; in 2017, it was selected into the "young talent examination project" of China Association for science and technology The research direction is molecular design and engineering preparation of covalent organic polymer (COP) In recent years, he has published more than 50 SCI papers in the journals of angelw Chem Int ed., J am Chem SOC., adv mater., energy & environ SCI., acsnano, nano energy, chem Eng SCI As the first author or corresponding author, and cited more than 2200 times by science and other SCI 16 invention patents and 4 authorizations have been applied for Cutting edge research achievements: non carbonated covalent organic polymer materials used in oxygen reduction catalysis covalent organic polymer materials (COP) have high specific surface area, precise and controllable pore structure, and good hydrothermal stability However, the poor conductivity of cop results in poor catalytic performance, which needs to be enhanced by subsequent high-temperature carbonization This process inevitably leads to the change or even destruction of cop structure Graphene has special single-layer two-dimensional honeycomb structure and excellent chemical and physical properties, such as: high specific surface area and charge transfer efficiency, good conductivity and chemical stability Therefore, the combination of cop and graphene can effectively improve the charge transfer efficiency of cop materials Through the self-assembly of cop and reduced graphene oxide (RGO), a new composite cop / RGO, namely catalyst cop-p-so3-co-rgo (4, right of Figure 1), was successfully prepared In order to obtain rich active sites, porphyrin analogues with high nitrogen content were used as monomers to prepare COP based electrocatalysts In order to accelerate the self-assembly of cop and RGO in the solution, the author first sulfonated cop, then connected metal ions (such as Co ions) with sulfonic groups and added them to the cop framework (Fig 1) Fig 1 The preparation of cop / RGO (source: angel Chem Int ed.) conductivity test results show that the conductivity of cop / RGO material is higher than that of COP by several orders of magnitude (from 3.06 × 10-9 to 2.56 × 10-1 SM-1), so that the non carbonized cop / RGO material has electrocatalytic activity The results of electrochemical performance test (Figure 2) show that the activity of oxygen reduction reaction (ORR) of cop / RGO is significantly improved, and cop / RGO has good stability in alkaline solution The active sites of catalyst 4 were analyzed comprehensively and deeply The toxic test results of SCN - showed that the orr properties of 4 were almost unchanged before and after SCN - addition, which indicated that CO 2 + in 4 skeleton was not the active site of orr, and there was no Co-N bond In order to verify this conclusion, the author has carried out the extended X-ray absorption fine structure (EXAFS) spectral analysis (Figure 3a), which shows that there is only one main peak at 1.5 Å, indicating that there is a co-O bond, and the Co-N peak or other high shell peak does not appear, which shows that the Co atom only coordinates with the O atom, which is in line with the above experimental conclusion Therefore, Co ions only accelerate the self-assembly of cop and RGO in the catalyst, but not in the catalyst In order to verify the universality of metal ions, iron, manganese, nickel and copper ions were used instead of cobalt ions Under the same conditions, the corresponding catalysts have similar orr performance and approximate starting potential (Fig 2f) Figure 2 Characterization of the electrochemical performance of the catalyst (source: angel Chem Int ed.) then, the author tested the X-ray absorption near edge structure (XANES) of CO and s in catalyst 4 before and after orr reaction (Figure 3) Comparing the XANES spectra of CO and s after reaction, the author found that there was no obvious change, indicating that CO and s almost did not participate in the orr process and were not the active center of orr The doping of electron rich nitrogen will make the carbon atoms around it positively charged, thus promoting the adsorption and activation of oxygen (O2) and improving the activity of orr Based on the above analysis, the author speculates that O 2 may be adsorbed on the carbon atom of porphyrin ring, which can be verified by the density functional theory (DFT) calculation Figure 3 EXAFS and XANES spectrogram analysis (source: angel Chem Int ed.) in order to understand the catalytic mechanism, the author established the atomic model of catalyst, and calculated the adsorption energy, overpotential and charge distribution of O2 and intermediate by DFT method (Figure 4) By comparing the adsorption energy of all possible adsorption sites, the author finally determined that the best active site is the carbon near pyrrole in the porphyrin ring, which is consistent with the results of XANES analysis In addition, the Bard effective charge distribution between cop and RGO is calculated The results show that there is almost no electron transfer between cop and RGO It is confirmed that the adsorption of macromolecular polymer on the surface of graphene will not change the electronic structure of graphene Based on the above experimental and theoretical analysis, the author concludes that the carbon next to pyrrole in porphyrin ring is the active center of orr Figure 4 DFT calculation results (source: angelw Chem Int ed.) Summary: the research group realized the development of electrocatalyst for oxygen reduction through non carbonized cop materials It is of great significance to develop electrocatalysts with clear active sites, high stability and good catalytic activity for clean energy conversion and storage This work was jointly completed by Xiang Zhonghua, Professor of Beijing University of chemical technology and Xia Zhenhai, Professor of North Texas University This research achievement was recently published in angelw Chem Int ed (DOI: 10.1002 / anie 201808226) The author of this paper is: Jianing Guo, chunyulin, Zhenhai Xia, and Zhonghua Xiang Today, people and scientific research are increasingly valued in economic life, China ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information, chembeango app, chembeango official microblog, CBG wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the domestic representative research group, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.