Table of Content

10 September 2022, Volume 43 Issue 9

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Content

Cover and Content of Chemical Journal of Chinese Universities Vol.43 No.9(2022)

2022, 43(9):  1. 

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Perspectives

Applications of Single-atom Catalysts in CO₂ Conversion

QIN Yongji, LUO Jun

2022, 43(9):  20220300.  doi:10.7503/cjcu20220300

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Single-atom catalyst（SAC）， emerging as a kind of promising catalyst materials with isolated active sites anchored on diverse matrixes， has shown excellent performances in thermocatalysis， photocatalysis and electrocatalysis due to their maximized efficiency of atoms and unique， adjustable electronic structure. Among all the reactions catalyzed by SAC， thermo/photo/electrocatalytic CO₂ conversion reaction（CCR） converts CO₂， the greenhouse gas， into fuels or value-added chemicals， which provides an effective strategy for solving the serious issues of global warming and energy shortage. In this perspective， based on the catalytic conversion of CO₂ by SAC， the research progresses in the field of CO₂ conversion reaction by SAC in recent years are summarized， the advantages and disadvantages of the synthetic methods， regulation and various CCRs are discussed， and the future development of SAC is prospected.



Charge Separation and Surface Reaction Mechanisms for Polymeric Single-atom Photocatalysts

TENG Zhenyuan, ZHANG Qitao, SU Chenliang

2022, 43(9):  20220325.  doi:10.7503/cjcu20220325

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In the past decade， a large number of single-atom catalysts（SACs） have been synthesized， and they exhibited excellent catalytic performance as well as high practical and cost advantages in photo-， electro-， thermo- catalysis. The uniqueness of the photocatalytic process determines that it is essentially different from the thermocatalytic and electrocatalytic processes， that is， electrons and holes at the excited state（rather than the valence electrons in the ground state） participate in the reaction. This perspective first discusses the difference between organic polymeric semiconductors and traditional inorganic semiconductors， clarifies that organic polymer semiconductors generally have small relative permittivity and the short distance between photogenerated electrons and holes（computationally， usually<1 nm）， resulting in almost absent band bending at the interface of polymetric photocatalysts. The introduction of metal ions into the matrix of organic semiconductors can form efficient donor- acceptor pairs， followed by an increased lifetime of charge carriers and improved carrier separation. In the process of designing high-efficiency polymer single-atom catalysts， the excited state charge distribution after the introduction of single-atom sites and the driving force of trapped electrons on different reactions are crucial to the overall activity of the catalysts. Time-space population analysis for wavefunction analysis and transient absorption spectroscopy can provide useful information for researchers. In the near future， with the further development of artificial intelligence， establishing an energy function with a regression accuracy close to or reaching the density functional theory level to invert the energy change of the system in the excited state is expected to establish a reliable connection between the excitation property and the activity of the photocatalytic reaction. Furthermore， the role of ligands and solvation should also be carefully considered in future studies.



Application of Single-atom Catalysis in Marine Energy

TANG Quanjun, LIU Yingxin, MENG Rongwei, ZHANG Ruotian, LING Guowei, ZHANG Chen

2022, 43(9):  20220324.  doi:10.7503/cjcu20220324

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The ocean is an important energy treasure house for human society in the future， and contains huge reserves of energy in various forms. Catalytic technology is a key technology to improve the utilization efficiency and conversion of energy and resources， and it is even more important in terms of the huge resource reserves of the ocean. Single-atom catalyst have excellent tunability， high selectivity， and high active site utilization. Therefore， single- atom catalysts compatible with the marine environment show superior application potential. Herein， the research progress of single-atom catalysis in the fields of marine hydrogen energy， marine energy conversion and seawater uranium extraction is systematically summarized. Moreover， comprehensive perspectives are given to guide the further research and development of single-atom catalysis in marine energy.



Techno-economic Analysis and Industrial Application Prospects of Single-atom Materials in CO₂ Catalysis

WANG Xintian, LI Pan, CAO Yue, HONG Wenhao, GENG Zhongxuan, AN Zhiyang, WANG Haoyu, WANG Hua, SUN Bin, ZHU Wenlei, ZHOU Yang

2022, 43(9):  20220347.  doi:10.7503/cjcu20220347

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In recent years， with the intensive scientific research， single-atom catalysts（SACs） have been widely explored and utilized due to their outstanding features such as high activity and high selectivity. As a bridge connec?ting heterogeneous and homogeneous catalysis， study of SACs has become one of the most important courses in the catalytic field and has broad industrial application prospects. This paper firstly gives a brief overview of the development history， characteristics and applications of SACs， and then summarizes the current techno-economic analysis in the field of CO₂ reduction and presents the first techno-economic calculations for single-atom materials. Finally， the future industrial applications of SACs in CO₂ reduction and the key scientific and technical issues to be solved are also discussed.



Progress and Perspective on Molybdenum Disulfide with Single-atom Doping Toward Hydrogen Evolution

LIN Gaoxin, WANG Jiacheng

2022, 43(9):  20220321.  doi:10.7503/cjcu20220321

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Layered molybdenum disulfide（MoS₂） has attracted much attention in electrochemical hydrogen generation due to its unique physicochemical properties. The hydrogen inert surface of MoS₂ results in the inferior hydrogen evolution reaction（HER） activity to Pt in both acid and alkaline media. Confining single atoms（SAs） on MoS₂ is a promising method to activate the basal plane， making MoS₂ an advanced HER electrocatalyst. Herein， this perspective starts with the structure of SA-MoS₂， and discusses the role of SAs for enhanced catalytic activity. Subsequently， synthesis methods， characterization techniques and recent progress of SA-MoS₂ are summarized. It highlights the importance of surface defects induced by SAs in activated basal plane to achieve high electrocatalytic performance. Finally， based on the progress of SA-MoS₂ in HER， this perspective presents general guidelines and research challenges in this promising field.



Review

Application of XAFS Technique in Single-atom Electrocatalysis

WANG Sicong, PANG Beibei, LIU Xiaokang, DING Tao, YAO Tao

2022, 43(9):  20220487.  doi:10.7503/cjcu20220487

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X-Ray absorption fine spectroscopy（XAFS） is a material characterization technique developed since 1980s. Because of its sensitivity to the local structure and chemical environment of central absorption atoms， it is very suitable for the characterization of single-atom catalysts. Basing on the principles and features of XAFS technique， this review deeply discussed the unique role of XAFS technology in several application scenarios involving single-atom catalysts， such as electrocatalytic water splitting， fuel cell cathode reaction and carbon dioxide electrochemical reduction. What’s more， this review predicted the future application prospects of XAFS technology in the field of single-atom electrocatalysis， expecting to give a hint to further and more specific characterization towards the structure and electrocatalytic mechanism of single-atom catalysts.



Single-atom and Cluster Photocatalysis： Competition and Cooperation

LIN Zhi, PENG Zhiming, HE Weiqing, SHEN Shaohua

2022, 43(9):  20220312.  doi:10.7503/cjcu20220312

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Photocatalytic technology has been considered as a promising and sustainable technology to convert solar energy to storable chemical energy. With active sites（single metal atoms and clusters） atomically dispersed on the semiconductor， the mass and charge transfer in photocatalysis can be significantly promoted， and the photocatalytic performance can be remarkably improved. However， it is still controversial whether clusters or single-atoms are the real active sites in catalysts. In this review， the recent advances in single-atom photocatalysis are briefly introduced， with the competition and synergy of single-atoms and clusters analyzed and discussed. Then， the state-of-the-art technologies in the identification and characterization of single-atoms and clusters as photocatalytic active sites are presented. Finally， the future development of single-atoms/clusters synergistic photocatalysis in solar-chemical energy conversions such as water splitting and CO₂ reduction is prospected.



Synchrotron Radiation X-Ray Absorption Spectroscopy Research Progress on Platinum Single-atom Catalysts

REN Shijie, QIAO Sicong, LIU Chongjing, ZHANG Wenhua, SONG Li

2022, 43(9):  20220466.  doi:10.7503/cjcu20220466

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As comparison with bulk materials， platinum single-atom catalysts（Pt SACs） that possess almost 100% noble-metal utilization， superior catalytic activity and homogeneous reactive sites， generally emerge as a promising frontier. The interfacial interactions between highly dispersed Pt atoms and supports largely determine their chemical and physical properties. Hence， constructing the real correlation between metal-support interactions and catalytic performances is essential to guide the optimization design of Pt SACs. Thanks to high flux， high collimation and wide-range wavelengths from synchrotron radiation light source， X-ray absorption spectroscopy（XAS） exhibits unparalleled capacity in the identification of electronic structure and local coordination of SACs. In this prospection， we aim to briefly discuss the synchrotron-radiation XAS research progress on Pt SACs. The unique interaction between Pt and multiply supports， such as metal oxides， metals， nanocarbons and porous organic frameworks， is highlighted in order to give better understanding on the influence mechanism. Ultimately， high-resolution characterizations on Pt SACs based on new synchrotron radiation techniques are prospective and recommended.



Freezing Synthesis for Single Atom Materials

WANG Ruyue, WEI Hehe, HUANG Kai, WU Hui

2022, 43(9):  20220428.  doi:10.7503/cjcu20220428

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In recent years， high-performance single-atom catalysts with maximum metal atom utilization efficiency have become a hot research topic in the field of energy storage and conversion. The high activity of single-atom catalysts is mainly due to their low-coordination environment of metal centers， quantum size effect， and metal- support interaction. Therefore， it is of great significance to develop a general and simple synthetic pathway for high-performance single-atom catalysts based on the structure-activity relationship. Considering industrial applications， wet chemistry synthesis has been considered a promising method for the preparation of single-atom catalysts owing to its simplicity and practicality of massive production. A series of strategies have also been developed for the preparation of supported single-atom catalysts. In this review， we summarized the unique freezing synthetic method to synthesize single-atom materials from the perspective of inhibiting the nucleation of metal species. We further systematically discuss the synthesis mechanism and the catalytic mechanism of the prepared supported single-atom catalysts for extensive applications. Finally， some prospects on the trend of future research in this respect are given.



Recent Progress of Single-atom Materials in Electrochemical Biosensing

JIANG Bowen, CHEN Jingxuan, CHENG Yonghua, SANG Wei, KOU Zongkui

2022, 43(9):  20220334.  doi:10.7503/cjcu20220334

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Electrochemical sensors have become one of the important development directions for the rapid detection of biosensing on the basis of their fast response， strong specificity and high accuracy， but it is currently difficult to achieve the detection level of single biomolecules， mainly originating from the key probe materials. Single-atom materials featuring their simple and well-defined atomic localized structures have received extensive attention in the field of electrochemical biosensing due to a unified active site rivaling biological enzymes. Herein， the synthesis of single-atom materials with a homogeneous local coordination environment and their applications in electrochemical biosensing are reviewed. Moreover， the challenges and opportunities of single-atom materials in electrochemical biosensing are furtherly outlooked.



Progress in Synthesis and Energy-related Electrocatalysis of Single-atom Catalysts

YAO Qing, YU Zhiyong, HUANG Xiaoqing

2022, 43(9):  20220323.  doi:10.7503/cjcu20220323

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Energy storage and conversion technology based on electrochemical reactions provide a green and sustainable way for the transformation of global energy structure， in which electrocatalysts with high efficiency play an important role. Benefitting from its unique advantages in physical and chemical properties， single-atom catalysts have shown great application prospects in electrocatalytic energy conversion. Herein， we review the progress in synthesis and energy-related electrocatalysis of single-atom catalysts. Firstly， the common characterization methods of single-atom catalysts are introduced. Subsequently， the synthesis methods of single-atom catalysts are summarized， including wet-chemical method， high temperature pyrolysis method， atomic deposition method， electrochemical deposition method， etc. Then， the research progress of these materials in oxygen reduction， carbon dioxide electroreduction， water electrolysis and nitrogen electroreduction reactions are introduced， with an emphasis on the relationship between structure of the catalyst and its performance. Finally， the current challenges and prospects in this field are discussed.



Article

Construction of Cobalt Single Atoms via Double-confinement Strategy for High-performance Electrocatalytic Reduction of Carbon Dioxide

WU Yu, LI Xuan, YANG Hengpan, HE Chuanxin

2022, 43(9):  20220343.  doi:10.7503/cjcu20220343

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In this manuscript， zinc， cobalt co-doped metal organic frameworks（MOFs） nanoparticles（ZnCo-ZIF） were mixed with polyacrylonitrile（PAN） to form a precursor solution. After electrospinning and high temperature pyrolysis， a porous carbon nanofiber supported single-atom cobalt catalyst（A-Co@PCF） was obtained. During high-temperature pyrolysis， polyacrylonitrile decomposed and carbonized to form the main body of carbon nanofibers. The collapse of MOFs nanoparticle structure and the volatilization of zinc components created the hierarchically porous structure throughout the nanofibers. Due to the double confinement of carbon nanofibers and pore structure， cobalt components cannot aggregate into cobalt nanoparticles， but cobalt components generate highly dispersed cobalt single atoms. Electrochemical tests show that the cobalt monoatomic catalyst can successfully reduce carbon dioxide to carbon monoxide， and the Faraday efficiency of carbon monoxide can reach 94% at ?0.66 V（vs. RHE） cathode potential. And after 60 h of durability test， its catalytic performance has no obvious performance attenuation， showing high stability. The high activity and stability of A-Co@PCFs can be attributed to the porous structure of the material and highly dispersed cobalt atoms， which also makes it possible to replace precious metal catalysts. In addition， this method also provides a reference for the synthesis of other transition metal single-atom catalysts.



Synergistic Catalysis Between Ir Single Atoms and Nanoparticles for N₂O Decomposition

YANG Jingyi, LI Qinghe, QIAO Botao

2022, 43(9):  20220388.  doi:10.7503/cjcu20220388

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“Atom trapping” is one of the effective methods to prepare thermally stable single-atom catalysts（SACs） at high temperature. However， the SACs derived from such methods often suffer from poor activity， which inhibits their application. Therefore， developing the application of these SACs is highly desired. In this work， we found that the Ir SACs prepared via atom trapping are inactive towards N₂O decomposition， but exhibit a synergistic effect with Ir nanoparticles（NPs） after loading the nanoparticle counterparts. X-ray photoelectron spectroscopy（XPS） and in situ diffuse reflectance infrared spectroscopy of CO adsorption（CO-DRIFTs） characterization combined with kinetic analysis revealed that the metallic Ir NPs are the real active sites in this reaction. Although Ir single atoms（SAs） with high valance state cannot directly activate the N₂O， they change the electronic state and adsorption ability of Ir NPs. O₂ temperature programmed desorption（O₂-TPD） verified that the presence of SAs stimulate the desorption of O₂ from Ir NPs thus enhance activity. This work provides new insights into the catalytic role of SAs.



Integration of Atomically Dispersed Ga Sites with C₃N₄ Nanosheets for Efficient Photo-driven CO₂ Cycloaddition

YANG Jingyi, SHI Siqi, PENG Huaitao, YANG Qihao, CHEN Liang

2022, 43(9):  20220349.  doi:10.7503/cjcu20220349

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A carbon nitride（C₃N₄）-based catalyst featuring high density of atomically dispersed Ga species（mass fraction of 8.42%） was rationally fabricated（Ga-C₃N₄） based on a molecule-confined strategy for photo-driven cycloaddition of CO₂ and epoxides. The atomically dispersed Ga sites and uniform N species in Ga-C₃N₄ served as Lewis acid and Lewis base sites， respectively， cooperating together to promote the activation of substrates. Compared with the thermal-driven catalytic system， the light irradiation favors the photo-generated electron transfer from catalyst（i.e.， Ga-C₃N₄） to epoxides， facilitating the catalytic efficiency of ring-opening step（i.e.， rate-limiting step）. As a result， Ga-C₃N₄ exhibited superior catalytic performance towards the CO₂ cycloaddition with epoxides under light irradiation.



Nitrogen Doped Ultra-thin Carbon Nanosheet Composited Platinum-ruthenium Single Atom Alloy Catalyst for Promoting Electrochemical Hydrogen Evolution Process

FAN Jianling, TANG Hao, QIN Fengjuan, XU Wenjing, GU Hongfei, PEI Jiajing, CEHN Wenxing

2022, 43(9):  20220366.  doi:10.7503/cjcu20220366

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In order to reduce the amount of precious metals， reduce costs and increase the possibility of large-scale production， the construction of single atom alloy（SAA） is a very feasible solution. Herein， an electrocatalyst with ultra-small PtRu single atom alloy species evenly dispersed on nitrogen doped ultra-thin carbon nanosheets（PtRu SAA/NC） was designed， and its structure was confirmed by synchrotron-radiation-based X-ray absorption fine structure（XAFS） spectroscopy. Compared with pure Ru clusters and nitrogen doped carbon sheets， the PtRu SAA/NC possesses higher hydrogen evolution reaction（HER） catalytic activity and exceptional stability， which exhibits a small Tafel slope of 43 mV/dec and a low overpotential of 54 mV at 10 mA/cm² during HER in 0.5 mol/L H₂SO₄ solution. The design of this low-cost and high-efficiency single atom alloy catalyst provides a new research direction for the development of clean energy structure conversion.



S-doped Fe-N-C as Catalysts for Highly Reactive Oxygen Reduction Reactions

CHENG Qian, YANG Bolong, WU Wenyi, XIANG Zhonghua

2022, 43(9):  20220341.  doi:10.7503/cjcu20220341

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In this paper， a series of S-doped Fe-N-C catalysts were prepared by introducing Fe（NO₃）₃·9H₂O and KSCN in a methanol-water two-solvent system using microwave heating and high-temperature pyrolysis techniques with ZIF-8 as the precursor. The results were analyzed by several characterization means such as X-ray powder diffraction， scanning transmission electron microscopy， and nitrogen adsorption and desorption tests. The results indicated that the reasonable introduction of both Fe and S resulted in Fe₃C/Fe-SAS@SNC catalysts with obvious graded porous structure and specific surface area of 673 m²/g， which exhibited excellent catalytic performance for oxygen reduction in both acid and alkaline electrolytes. In 0.1 mol/L KOH， the half-wave potential of the Fe₃C/Fe-SAS@SNC was 0.880 V（vs. RHE）， which is higher than that of commercial Pt/C catalysts， and exhibited better stability than commercial Pt/C. In addition， the Fe₃C/Fe-SAS@SNC electrocatalytic oxygen reduction performance in 0.5 mol/L H₂SO₄ is similarly comparable to that of commercial Pt/C catalysts.



Single-atom Cerium Sites Designed for Durable Oxygen Reduction Reaction Catalyst with Weak Fenton Effect

CHU Yuyi, LAN Chang, LUO Ergui, LIU Changpeng, GE Junjie, XING Wei

2022, 43(9):  20220294.  doi:10.7503/cjcu20220294

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Metal-Nitrogen-Carbon（M-N-C） materials has hitherto been the most promising alternative to platinum for catalyzing the oxygen reduction reaction. However， severe degradation issues have been reported under operando testing condition， such as free radical attack generated by the Fenton reaction and the leaching of active sites， which restricted the further advance of M-N-C catalysts. Herein， single-atom Ru，Ce-N-C catalyst with Ru-N _x active sites with weak fenton effect and Ce-N _x sites as free radical scavenger was synthesized. The results indicated that Ru， Ce-N-C catalyst exhibits excellent oxygen reduction reaction（ORR） activity［E_1/2=0.78 V（vs. RHE）］ and outstanding stability（8 mV negative shift after 30000 cycles）， which is superior to Fe-N-C catalyst. The electron transfer number（n） of Ru， Ce-N-C was 3.98， and the average H₂O₂ yield for Ru， Ce-N-C was less than 5%. This work opens the new path for improving the durability of M-N-C catalysts in fuel cells.