Professor Zhang Jiatao, Researcher Zhao Di, Professor Chen Chen of Tsinghua University and others EES research articles: Atomic engineering of oxygen-rich metal organic frameworks, Fe1N2O2 interface structure promotes efficient electrochemical reduction of CO2
article information
article information
Atomic engineering of oxygen-rich metal organic frameworks, Fe1N2O2 interface structure promotes efficient electrochemistry and Original CO2
First author: Zhao Di, Yu Ke, Song Pengyu
Corresponding author: Zhao Di*, Liu Shoujie*, Zhang Jiatao*, Chen Chen*
Unit: Beijing Institute of Technology, Tsinghua University
Research background
electrochemical conversion of carbon dioxide provides a way to produce fuel and raw materials. In different CO2 electrochemical reduction (CO2RR) pathways, the generation of carbon monoxide (CO) through 2 electron transfer reaction is the first step in converting it into a more complex product and is also considered one of the most economical CO2 reduction pathways. Among various M-N-C catalysts, Fe-N-C has a common FeNx coordination structure and is expected to replace traditional precious metal-based CO2RR catalysts in the near future.
For Fe-NC type electrocatalysts, the formation of *COOH requires a large energy barrier. Since *CO is relatively strong in binding at the active site, it is also difficult to desorption of CO. Therefore, the key to improving the CO2-CO conversion efficiency of Fe-N-C electrocatalyst is to promote *COOH generation (protonation) and optimize the binding strength (desorption) of *CO. The electronegativity of heteroatom O is stronger than that of the most common N, which is of great significance to regulating the microenvironment of Fe single atoms and improving catalytic performance.
The traditional ZIF-8 is the most common MOF backbone, but because there is an M-N coordination bond in the parent ZIF structure, the SACs obtained by pyrolysis are always M-N4 coordination configuration. O atoms are introduced externally. At a pyrolysis temperature greater than 500℃, O atoms are very easy to volatilize and difficult to obtain Fe-O coordination catalysts. At present, it is urgent to find a new MOF carrier to help form Fe-O coordination during high-temperature pyrolysis, regulate the Fe atomic interface, and promote efficient electrochemical reduction of CO2.
Article introduction
Based on this, Professor Zhang Jiatao from Beijing Institute of Technology, Researcher Zhao Di, and Professor Chen Chen and Professor Liu Shoujie from Tsinghua University, have collaborated with , and published the title "Atomic-Level Engineering Fe1N2O2 Interfacial Structure Derived from Oxygen-Abundant Metal–Organic Frameworks to Promote Electrochemical CO2 Reduction” research article.
This paper uses Zn-MOF-74 as an oxygen-rich precursor for synthesis and regulation. Fe/Zn-MOF-74 is obtained by doping Fe ions, introduced into N source and calcined, and finally obtained Fe1N2O2/NC catalyst with a special coordination structure. The catalyst is within a wide potential window of -0.4V to -0.8V, and the CO Faraday efficiency remains above 95%. It is worth pointing out that at -0.5V, the CO Faraday efficiency reaches even up to 99.7%, almost close to 100%.
In addition, the formation mechanism of Fe1N2O2/NC is revealed through the analysis of the synchronous radiation results of the calcined product at different temperatures. Theoretical calculations show that compared with traditional Fe-N4 catalysts, the introduction of O and N together to regulate the Fe atomic interface has significant advantages in electrocatalyzed carbon dioxide reduction to produce CO. The unique coordination structure of Fe1N2O2 shows small free energy changes in the generation of intermediate COOH* and the desorption steps of CO, thereby accelerating the reaction kinetics and improving catalytic performance.
This article’s key points
Key points 1: Unique catalyst structure design
is different from the most common ZIF-8 carrier. This work uses FE-doped Zn-MOF-74 as the precursor for synthesis and regulation. Fe occupies the Zn site in the original MOF and coordinates with O atoms in the organic ligand, and further introduces an N source. Under high-temperature calcination, Zn evaporates, and the Fe-O coordination cluster will be replaced by partial Fe-N coordination, and finally a Fe1N2O2/NC catalyst with a special coordination structure is obtained. This structure is effectively verified by XPS and synchronous radiation results.
The good rod-shaped morphology of Fe1N2O2/NC can be observed through the TEM and HRTEM characterization results. The EELS point spectrum obtained by HAADF-STEM further strongly proves the coexistence of Fe, O, and N in Fe1N2O2/NC, indicating that a single iron is co-anchored by N and O inside C. Through this synthetic design, the problem of difficult to obtain Fe-O bonds with ZIF-8 as a precursor is effectively solved.
Figure 1. Preparation process and morphological characterization of Fe1N2O2/NC.
1 Key points 2: Research on the Fe1N2O2/NC structure generation process
Figure 2. Analysis of the formation process of Fe1N2O2/NC catalyst through N2 adsorption-desorption isotherm, XPS, FeK side synchronous radiation, etc.
By analyzing the BET and morphology at different stages such as the introduction of N sources and the introduction of N sources, it was concluded that the introduction of N sources can not only help maintain morphology, but also help the formation of Fe single atoms. The XRD, XPS and synchronous radiation characterization of the calcined product at different temperatures (0°C, 250°C, 500°C, 750°C and 1000°C) was performed to study the catalyst structure generation process. Fe k-side XANES spectroscopy showed that samples calcined at different temperatures had a major peak at 1-2 Å, which could be attributed to the first shell metal-N/O.
As the reaction temperature increases, the peak intensity decreases, and the peak position slightly shifts to the left, indicating that the local coordination number decreases accordingly, forming a coordinate configuration of mixed Fe-N/O. Quantitative EXAFS analysis showed that before pyrolysis, the first shell of the Fe atom consisted of Fe-O bonds with a coordination number of 6 (5 from organic ligands and 1 from adsorbed O species). After carbonization at 500°C, the adsorbed O2 or water is removed, and the average coordination number of the intermediate is 5. When the temperature further rises to 750°C, the average coordination number decreases to 4.7, and the 0Fe-N scattering path appears, indicating that the N atoms in the ammonia begin to replace the O atoms in the frame. Finally, Fe1N2O2/NC catalyst was obtained at 1000°C with a coordination number of about 4.
Keypoint 3: Excellent CO2RR-CO performance
The electrochemical CO2 reduction performance of these catalysts was evaluated in CO2 saturated 0.1 M KHCO3 solution. As can be seen from the LSV curve, Fe1N2O2/NC has a smaller starting potential for the reversible hydrogen electrode (RHE) at -300 mV and a higher current density within the measured potential range than NC and Fen/C. In a typical three-electrode H-type battery, CO2 constant potential electrolysis is further performed at different potentials.
At -0.7 V, the jCO of Fe1N2O2/NC is as high as 6.5 mA cm-2, which is much higher than the comparison samples at the same potential (NC is 1.5 mA cm-2, Fen/C is almost 0 mA cm-2). The selectivity of Fe1N2O2/NC electrocatalysts is as high as 95% in the extremely wide potential range of -0.4 - 0.8 V. It is worth noting that at -0.5 V, FECO is as high as 99.7%, which is better than most currently reported Fe single-atom catalysts. Electrolyzed at -0.7V potential for 12 h, the CO Faraday efficiency and bias current density attenuation were negligible, showing excellent stability.
Keypoint 4: DFT calculation further reveals the excellent performance mechanism
In order to reveal the impact of plane coordination of O and N atoms on the Fc bits, we conducted a series of density functional theory DFT calculations. A model in which Fe1N2O2, Fe1N4 and Fe1N3O, Fe1NO3 and Fe1O4 embedded N-doped carbon was constructed. The calculation shows that as the number of coordination O increases, it is more conducive to the generation of *COOH. Compared with other models, the Fe1N2O2 configuration is most conducive to the desorption of CO. Compared with Fe1N2O2, the Fe position in Fe1N4 is more likely to adsorb CO, which is not conducive to CO desorption.
CO@Fe1O4's PDOS has obvious spin polarization, so CO molecules will be firmly trapped on the catalyst surface, thereby increasing the difficulty of CO desorption. The charge density results show that due to strong spin polarization and less electron loss, most of the electrons are concentrated on CO, resulting in strong adsorption and difficulty in desorption of CO. In addition, compared with other models, the Bader changes in Fe sites between CO@Fe1N2O2 and Fe1N2O2 have the greatest difference, further indicating that CO@Fe1N2O2 is easier to release adsorbed CO than other models, thereby improving reaction performance.
Article link
Atomic-Level Engineering Fe1N2O2 Interfacial Structure Derived from Oxygen-Abundant Metal–Organic Frameworks to Promote Electrochemical CO2 Reduction
https://pubs.rsc.org/en/content/articlelanding/2022/ee/d2ee00878e
DOI: 10.1039/d2 ee00878e
Author profile
Zhang Jiatao, currently professor at the School of Chemistry and Chemical Engineering and School of Materials, Beijing Institute of Technology. Fellow of the Royal Chemistry Society of the United Kingdom, Deputy Editor-in-Chief of Energy Materials Advances Journal, Senior Member of the Chinese Chemical Society, Member of the Chemical Engineering Professional Committee of the Chinese Chemical Engineering Society, Deputy Secretary-General of the Nanomaterials and Devices Branch, and Director of the Chinese Materials Research Society. He graduated from Tsinghua University with a Ph.D. He has been engaged in postdoctoral research at the Institute of Inorganic Chemistry of the University of Karlsruhe in Germany and the University of Maryland in the United States.
The main research directions are semiconductor doped quantum dot chemical synthesis and photoelectric new energy devices application, semiconductor composite nanomaterial chemical synthesis and photocatalytic application research, semiconductor composite nanomaterial chemical synthesis and biomedical research. He presided over 8 provincial and ministerial projects such as the National Natural Science Foundation of China, Beijing, and the Ministry of Education; participated in 2 key and major integrated projects of the National Natural Science Foundation of China. To date, he has published more than 70 academic papers in domestic and foreign academic journals and conferences, including more than 60 in SCI, 2 in EI, and 7 authorized patents.
Zhao Di , received her doctorate degree from Beijing Institute of Technology in 2017. In the same year, he worked as a postdoctoral fellow in the Department of Chemistry at Tsinghua University. He joined Beijing Institute of Technology in 2020 and is currently an associate professor at the School of Chemistry and Chemical Engineering. Research directions include nano, clusters, single-atom catalyst synthesis and catalytic performance research.
Related research results have published nearly 20 related papers in international academic journals such as J. Am. Chem. Soc., Angew. Chem. Int. Ed., Chem. Soc. Rev., Energy Environ. Sci., Nano Energy, Chem. Mater. , and some of them have been invited to cover magazines and have been reported by C&EN, including 3 highly cited papers. An international patent is authorized. Received the second postdoctoral innovation talent support program. As the project leader, he has undertaken projects on the China Postdoctoral Science Foundation and participated in projects such as the National Natural Science Foundation of China and horizontal corporate projects.
Chen Chen, currently a professor in the Department of Chemistry of Tsinghua University. He obtained a bachelor's degree from Beijing Institute of Technology in 2006, a doctorate from Tsinghua University in 2011, and worked in postdoctoral research at the University of California, Berkeley and Lawrence Berkeley National Laboratory from 2011 to 2014. He has taught in the Department of Chemistry at Tsinghua University since 2015.
mainly engages in research in the fields of inorganic materials, catalysis, etc. More than 60 papers have been published in academic journals such as Science, Nat. Chem., Nat. Catal., Nat. Commun., J. Am. Chem. Soc., Angew. Chem. Int. Ed., Adv. Mater., etc. In 2018, he received the support of the Beijing Outstanding Youth Science Foundation and won the Youth Chemistry Award of the Chinese Chemistry Association; in 2019, he received the support of the National Outstanding Youth Science Foundation.
