扫描电子显微技术与表征技术的发展与应用

扫描电镜是研究材料微观结构的有力工具,电子显微技术与表征技术的发展,进一步推动了扫描电镜在材料各领域应用。随着各领域研究方向的细分化和应用需求的差异化,扫描电子显微技术与表征技术出现了差异化发展趋势,这极大丰富了商品化SEM产品类别。扫描电子显微技术的主要发展方向有高分辨率、低加速电压、低真空工作环境、大样品仓、大探针电流、电镜微型化等。电子显微表征技术的主要发展方向有高通量快速表征、显微表征原位化、样品结构信息采集三维化、电镜功能集成一体化等。

In situ studies of energy-related electrochemical reactions using Raman and X-ray absorption spectroscopy

Electrochemical energy conversion technologies involving processes such as water splitting and O_(2)/CO_(2) reduction,provide promising solutions for addressing global energy scarcity and minimizing adverse environmental impact.However,due to a lack of an in-depth understanding of the reaction mechanisms and the nature of the active sites,further advancement of these techniques has been limited by the development of efficient and robust catalysts.Therefore,in situ characterization of these electrocatalytic processes under working conditions is essential.In this review,recent applications of in situ Raman spectroscopy and X-ray absorption spectroscopy for various nano-and single-atom catalysts in energy-related reactions are summarized.Notable cases are highlighted,including the capture of oxygen-containing intermediate species formed during the reduction of oxygen and oxidation of hydrogen,and the detection of catalyst structural transformations occurring with the change in potential during the evolution of oxygen and reduction of CO_(2).Finally,the challenges and outlook for advancing in situ spectroscopic technologies to gain a deeper fundamental understanding of these energy-related electrocatalytic processes are discussed.

Identifying the active sites in C-N codoped TiO_(2) electrode for electrocatalytic water oxidation to produce H_(2)O_(2)

Unveiling the active site of an electrocatalyst is fundamental for the development of efficient electrode material.For the two-electron water oxidation to produce H_(2)O_(2),competitive reactions,including four-and one-electron water oxidation and surface reconstruction derived from the high-oxidative environment co-existed,leading to great challenges to identify the real active sites on the electrode.In this work,Ti/TiO_(2)-based electrodes calcined under air,nitrogen,or urea atmospheres were selected as electrocatalysts for two-electron water oxidation.Electrochemical analyses were applied to evaluate the catalytic activity and selectivity.The morphological and current change on the electrode surface were determined by scanning electrochemical microscopy,while the chemical and valence evolutions with depth distributions were tested by XPS combined with cluster argon ion sputtering.The results demonstrated that Ti/TiO_(2) nanotube arrays served as the support,while the functional groups of carbonyl groups and pyrrolic nitrogen derived from the co-pyrolysis with urea were the active sites for the H_(2)O_(2) production.This finding provided a new horizon to design efficient catalysts for H_(2)O_(2) production.

Coordination environment of active sites and their effect on catalytic performance of heterogeneous catalysts

The structural complexity of supported metal catalysts,playing significant role in a wide range of chemical technologies,have prevented us from deeply understanding their catalytic mechanisms at atomic level.A fundamental understanding of the nature of active sites and structure–performance relationship of supported metal catalysts from a comprehensive view will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy conversion and environmental protection.This review surveys the effects of multiple factors,including the metal size,shape,support,alloy and ligand modifier,on the coordinated environment of active center and further their influence on the catalytic reactions,aiming to provide guidance for the design of industrialized heterogeneous catalysts with extraordinary performance.Subsequently,the key structure characterization techniques in determining the coordination structure of active metal sites,especially the dynamic coordination structure change under the reaction condition,are well summarized.A brief summary is finally provided together with personal perspectives on the further development in the field of heterogeneous metal catalysts.

Single atom‐based catalysts for electrochemical CO_(2) reduction

Electrochemical CO_(2) reduction reaction(CO_(2)RR),powered by renewable energy,emerges as a promising approach against environmental issues and energy crisis by converting CO_(2) into val‐ue‐added chemicals.Single atom catalysts(SACs)with isolated metal atoms dispersed on supports exhibit outstanding performance for CO_(2) electroreduction,because of their strong single at‐om‐support interactions,maximum metal utilization and excellent catalytic activity.However,SACs suffer from agglomeration of particles,low metal loading,and difficulty in large‐scale production.In addition,molecular catalysts as another single atom‐based catalyst,consisting of ligands molecules connected to metal ions,exhibited similar metal‐nitrogen(M‐N)active centers as that in met‐al‐nitrogen‐carbon(M‐N‐C)SACs,which were highly active to CO_(2) reduction due to their well‐defined active sites and tunability over the steric and electronic properties of the active sites.Nonetheless,molecular catalysts are challenged by generally moderate activity,selectivity and sta‐bility,poor conductivity and aggregation.Many works have been devoted to overcoming these is‐sues of SACs and molecular catalysts for efficient CO_(2)RR,but only limited reviews for systematic summary of their fabrication,application,and characterizations,which were highlighted in this review.Firstly,we summarize recent advanced strategies in preparing SACs for CO_(2)RR,including wet‐chemistry approaches(defect engineering,spatial confinement,and coordination design),other synthetic methods and large‐scale production of SACs.Besides,electrochemical applications of SACs and molecular catalysts on CO_(2)RR are discussed,which involved the faradaic efficiency and partial current density of the desired product as well as the catalyst stability.In addition,ex‐situ and in‐situ/operando characterization techniques are briefly assessed,benefiting probing the active sites and understanding the CO_(2)RR catalytic mechanisms.Finally,future directions for the devel‐opment of single atom‐based catalysts(SACs,molecular catalysts)are pointed out.

Full life cycle characterization strategies for spatiotemporal evolution of heterogeneous catalysts

The sustainable development of the chemical industry requires novel and efficient catalysts and catalytic processes,especially eco-friendly and intrinsically safe processes.The idea is to improve the selectivity,activity,and stability of the catalyst in an appropriate reactor.Therefore,it is of great academic and industrial significance to conduct in-situ characterization of a working catalyst while testing its catalytic performance.This is beneficial for a comprehensive study on the dynamic evolution of the catalyst structure under real conditions,deepening the understanding of the structure-performance relationship of catalysts,and providing a scientific basis for the development of future generation catalytic technology.Thus far,it is still a great challenge to realize full life cycle characterization of heterogeneous catalysts from catalyst formation and function to deactivation under real world conditions.In this mini review,we summarize the characterization strategies for heterogeneous catalysts,using zeolite,metal,and metal oxide catalysts as typical examples.The research strategies for the approximation of industrial conditions,multi-scale in-situ characterization devices,and computational modeling of realistic conditions should provide insight for the research and development of industrial catalysis.

In-situ electrochemical surface-enhanced Raman spectroscopy in metal/polyelectrolyte interfaces

Polyelectrolyte becomes more and more popular in electrocatalysis.The understanding of electrode/polyelectrolyte interfaces at the molecular level is important for guiding further the polyelectrolyte-based electrocatalysis.Herein,we demonstrate an in-situ surface-enhanced Raman spectroscopic method by using a three-electrode spectroelectrochemical cell towards characterizing the electrode/polyelectrolyte interfaces.The Ag/AgCl and Ag/Ag_(2)O electrodes are used as the reference electrode in the acidic and the alkaline systems,respectively.The working electrode is made of a transparent carbon thin film which loads the electrocatalysts.The applications of this method are demonstrated through the in-situ characterizations of the p-methylthiophenol adsorbed on the Au and Pt and the electrochemical oxidation of Au on polyelectrolyte membranes.The potential-dependent spectral features of these two systems show that this method is a powerful tool for investigating the electrode/polyelectrolyte interfaces in electrocatalysis.

Restructuring of well-defined Pt-based electrode surfaces under mild electrochemical conditions

Since the 1980s,single-crystal Pt electrodes with well-defined surface structures have been deemed stable under mild electrochemical conditions(e.g.,in the potential region of electric double layers,underpotential deposition of hydrogen,or mild hydrogen evolution/OH adsorption)and have served as model electrodes for unraveling the structure-performance relation in electrocatalysis.With the advancement of in situ electrochemical microscopy/spectroscopy techniques,subtle surface restructuring under mild electrochemical conditions has been achieved in the last decade.Surface restructuring can considerably modify electrocatalytic properties by generating/destroying highly active sites,thereby interfering with the deduction of the structure-performance relation.In this review,we summarize recent progress in the restructuring of well-defined Pt(-based)electrode surfaces under mild electrochemical conditions.The importance of the meticulous structural characterization of Pt electrodes before,during,and after electrochemical measurements is demonstrated using CO adsorption/oxidation,hydrogen adsorption/evolution,and oxygen reduction as examples.The implications of present findings for correctly identifying the reaction mechanisms and kinetics of other electrocatalytic systems are also briefly discussed.

Surface-enhanced vibrational spectroscopies in electrocatalysis:Fundamentals,challenges,and perspectives

Electrocatalysis offers a promising approach towards chemical synthesis driven by renewable energy.Molecular level understanding of the electrochemical interface remains challenging due to its compositional and structural complexity.In situ interfacial specific characterization techniques could help uncover structure-function relationships and reaction mechanism.To this end,electrochemical surface-enhanced Raman spectroscopy(SERS)and surface-enhanced infrared absorption spectroscopy(SEIRAS)thrive as powerful techniques to provide fingerprint information of interfacial species at reaction conditions.In this review,we first introduce the fundamentals of SERS and SEIRAS,followed by discussion regarding the technical challenges and potential solutions.Finally,we highlight future directions for further development of surface-enhanced spectroscopic techniques for electrocatalytic studies.