In situ observation of the electrochemical behavior of Li–CO_(2)/O_(2)batteries in an environmental transmission electron microscope

Li–CO_(2)/O_(2)batteries,a promising energy storage technology,not only provide ultrahigh discharge capacity but also capture CO_(2)and turn it into renewable energy.Their electrochemical reaction pathways'ambiguity,however,creates a hurdle for their practical application.This study used copper selenide(CuSe)nanosheets as the air cathode medium in an environmental transmission electron microscope to in situ study Li–CO_(2)/O_(2)(mix CO_(2)as well as O_(2)at a volume ratio of 1:1)and Li–O_(2)batteries as well as Li–CO_(2)batteries.Primary discharge reactions take place successively in the Li–CO_(2)/O_(2)–CuSe nanobattery:(I)4Li^(+)+O_(2)+4e^(−)→2Li_(2)O;(II)Li_(2)O+CO_(2)→Li_(2)CO_(3).The charge reaction proceeded via(III)2Li_(2)CO_(3)→4Li^(+)+2CO_(2)+O_(2)+4e^(−).However,Li–O_(2)and Li–CO_(2)nanobatteries showed poor cycling stability,suggesting the difficulty in the direct decomposition of the discharge product.The fluctuations of the Li–CO_(2)/O_(2)battery's electrochemistry were also shown to depend heavily on O_(2).The CuSe‐based Li–CO_(2)/O_(2)battery showed exceptional electrochemical performance.The Li^–CO_(2)/O_(2)battery offered a discharge capacity apex of 15,492 mAh g^(−1) and stable cycling 60 times at 100 mA g^(−1).Our research offers crucial insight into the electrochemical behavior of Li–CO_(2)/O_(2),Li–O_(2),and Li–CO_(2)nanobatteries,which may help the creation of high‐performance Li–CO_(2)/O_(2)batteries for energy storage applications.

The mechanism of room-temperature oxidation of a HF-etched Ti3C2Tx MXene determined via environmental transmission electron microscopy and molecular dynamics

The oxidation chemistry of two-dimensional transition metal carbide MXenes has brought new research significance to their protection and application.However,the oxidation behavior and degradation mechanism of MXenes,in particular with time under oxygen conditions at room tem-perature,remain largely unexplored.Here,several experimental and theo-retical techniques are used to determine a very early stage of the oxidation mechanism of HF-etched Ti3C2Tx(a major member of MXenes and Tx=surface functional groups)in an oxygen environment at room temper-ature.Aberration-corrected environmental transmission electron micros-copy coupled with reactive molecular dynamics simulations show that the crystal plane-dependent oxidation rate of Ti3C2Tx and oxide expansion are attributed to differences in the coordination and charge of superficial Ti atoms,and the existence of the channels between neighboring MXene layers on the different crystal planes.The complementary x-ray photoelec-tron spectroscopy and Raman spectroscopy analyses indicate that the ana-tase and a tiny fraction of brookite TiO2 successively precipitate from the amorphous region of oxidized Ti3C2Tx,grow irregularly and transform to rutile TiO2.Our study reveals the early-stage structural evolution of MXenes in the presence of oxygen and facilitates further tailoring of the MXene per-formance employing oxidation strategy.

Revealing the dynamics of the alloying and segregation of Pt-Co nanoparticles via in-situ environmental transmission electron microscopy

Thermal treatment is a general and efficient way to synthesize intermetallic catalysts and may involve complicated physical processes.So far,the mechanisms leading to the size and composition heterogeneity,as well as the phase segregation behavior in Pt-Co nanoparticles(NPs)are still not well understood.Via in-situ environmental transmission electron microscopy,the formation dynamics and segregation behaviors of Pt-Co alloyed NPs during the thermal treatment were investigated.It is found that Pt-Co NPs on zeolitic imidazolate frameworks-67-derived nanocarbon(NC)are formed consecutively through both particle migration coalescence and the Ostwald ripening process.The existence of Pt NPs is found to affect the movement of Co NPs during their migration.With the help of theoretical calculations,the correlations between the composition and migration of the Pt and Co during the ripening process were uncovered.These complex alloying processes are revealed as key factors leading to the heterogeneity of the synthesized Pt-Co alloyed NPs.Under oxidation environment,the Pt-Co NPs become surface faceted gradually,which can be attributed to the oxygen facilitated relatively higher segregation rate of Co from the(111)surface.This work advances the fundamental understanding of design,synthesis,and durability of the Pt-based nanocatalysts.

Oxidation behavior of cobalt nanoparticles studied by in situ environmental transmission electron microscopy

The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to polycrystalline tricobalt tetroxide,in the presence of oxygen with a low partial pressure.Numerous cavities(or voids) were formed during the oxidation,owing to the Kirkendall effect.Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law,which was consistent with diffusion-limited kinetics.In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered.The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation,and formed the hollow structure.Irradiation by the electron beam,which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate,played an important role in activating and promoting the oxidations.These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.

In-situ imaging the electrochemical reactions of Li-CO_(2) nanobatteries at high temperatures in an aberration corrected environmental transmission electron microscope

Rechargeable lithium-carbon dioxide(Li-CO_(2))batteries have attracted much attention due to their high theoretical energy densities and capture of C0_(2).However,the electrochemical reaction mechanisms of rechargeable Lo-CO_(2) batteries,particularly the decomposition mechanisms of the discharge product Li_(2)CO_(3) are still unclear,impeding their practical applications.Exploring electrochemistry of Li_(2)CO_(3) is critical for improving the performance of Li-C0_(2) batteries.Herein,in-situ environmental transmission electron microscopy(ETEM)technique was used to study electrochemistry of Li_(2)CO_(3) in Li-C0_(2) batteries during discharge and charge processes.During discharge,Li_(2)CO_(3) was nucleated and accumulated on the surface of the cathode media such as carbon nanotubes(CNTs)and Ag nanowires(Ag NWs),but it was hard to decompose during charging at room temperature.To promote the decomposition of Li2C03,the charge reactions were conducted at high temperatures,during which Li_(2)CO_(3) was decomposed to lithium with release of gases.Density functional theory(DFT)calculations revealed that the synergistic effect of temperature and biasing facilitates the decomposition of Li_(2)CO_(3).This study not only provides a fundamental understanding to the high temperature Li-C0_(2) nanobatteries,but also offers a valid technique,i.e.,discharging/charging at high temperatures,to improve the cyclability of Li-CO_(2) batteries for energy storage applications.

Several major issues concerning the environmental transmission and risk prevention of SARS-CoV-2

Coronavirus disease 2019(COVID-19) is the most serious infectious disease pandemic in the world in a century, and has had a serious impact on the health, safety, and social and economic development of all mankind. Since the earth entered the“Anthropocene”, human activities have become the most important driving force of the evolution of the earth system. At the same time, the epidemic frequency of major human infectious diseases worldwide has been increasing, with more than 70% of novel diseases having zoonotic origins. The review of several major epidemics in human history shows that there is a common rule, i.e., changes in the natural environment have an important and profound impact on the occurrence and development of epidemics. Therefore, the impact of the natural environment on the current COVID-19 pandemic and its mechanisms have become scientific issues that need to be resolved urgently. From the perspective of the natural environment, this study systematically investigated several major issues concerning the environmental transmission and risk prevention of Severe Acute Respiratory Syndrome Coronavirus 2(SARS-CoV-2). From a macroscopic temporal and spatial scale, the research focus on understand the impact of the destruction of the natural environment and global changes on the outbreak of infectious diseases;the threat of zoonotic diseases to human health;the regularity for virus diffusion, migration and mutation in environmental media;the mechanisms of virus transmission from animals and environmental media to humans;and environmental safety, secondary risk prevention and control of major epidemics. Suggestions were made for future key research directions and issues that need attention, with a view to providing a reference for the prevention and control of the global coronavirus disease 2019, and to improving the ability of response to major public health emergencies.

Direct environmental TEM observation of silicon diffusion-induced strong metal-silica interaction for boosting CO_(2)hydrogenation

For the high-temperature catalytic reaction,revealing the interface of catalyst–support and its evolution under reactive conditions is of crucial importance for understanding the reaction mechanism.However,much less is known about the atomic-scale interface of the hard-to-reduce silica-metal compared to that of reducible oxide systems.Here we reported the general behaviors of SiO_(2)migration onto various metal(Pt,Co,Rh,Pd,Ru,and Ni)nanocrystals supported on silica.Typically,the Pt/SiO_(2)catalytic system,which boosted the CO_(2)hydrogenation to CO,exhibited the reduction of Si0 at the Pt-SiO2 interface under H2 and further Si diffusion into the near surface of Pt nanoparticles,which was unveiled by in-situ environmental transmission electron microscopy coupled with spectroscopies.This reconstructed interface with Si diffused into Pt increased the sinter resistance of catalyst and thus improved the catalytic stability.The morphology of metal nanoparticles with SiO_(2)overlayer were dynamically evolved under reducing,vacuum,and oxidizing atmospheres,with a thicker SiO_(2)layer under oxidizing condition.The theoretical calculations revealed the mechanism that the Si-Pt surface provided synergistic sites for the activation of CO_(2)/H_(2)to produce CO with lower energy barriers,consequently boosting the high-temperature reverse water-gas shift reaction.These findings deepen the understanding toward the interface structure of inert oxide supported catalysts.

Application of a DPC for PMD Compensation in Environmental Perturbed Transmission System

Polarization mode dispersion (PMD) compensation is presented on environmental perturbed fiber-optical transmission system in this paper. We achieve a dynamic polarization controller (DPC) to feedback control the PMD, successfully.

Environmental Stability and Transmissibility of Enveloped Viruses at Varied Animate and Inanimate Interfaces

Enveloped viruses have been the leading causative agents of viral epidemics in the past decade,including the ongoing coronavirus disease 2019 outbreak.In epidemics caused by enveloped viruses,direct contact is a common route of infection,while indirect transmissions through the environment also contribute to the spread of the disease,although their significance remains controversial.Bridging the knowledge gap regarding the influence of interfacial interactions on the persistence of enveloped viruses in the environment reveals the transmission mechanisms when the virus undergoes mutations and prevents excessive disinfection during viral epidemics.Herein,from the perspective of the driving force,partition efficiency,and viral survivability at interfaces,we summarize the viral and environmental characteristics that affect the environmental transmission of viruses.We expect to provide insights for virus detection,environmental surveillance,and disinfection to limit the spread of severe acute respiratory syndrome coronavirus 2.

In-situ imaging electrocatalysis in a solid-state Li-O_(2) battery with CuSe nanosheets as air cathode

The development of highly efficient catalysts in the cathodes of rechargeable Li-O_(2) batteries is a considerable challenge.To enhance the electrochemical performance of the Li-O_(2) battery,it is essential to choose a suitable catalyst material.Copper selenide(CuSe)is considered as a more promising cathode catalyst material for Li-O_(2) battery due to its better conductivity and rich electrochemical active sites.However,its electrochemical reaction and fundamental catalytic mechanism remain unclear till now.Herein,in-situ environmental transmission electron microscopy technique was used to study the catalysis mechanism of the CuSe nanosheets in Li-O_(2) batteries during discharge and charge processes.It is found that Li_(2)O was formed and decomposed around the ultrafine-grained Cu during the discharge and charge processes,respectively,demonstrating excellent cycling.This indicate that the freshly formed ultrafine-grained Cu in the conversion reaction catalyzed the latter four-electron-transfer oxygen reduction reaction,leading to the formation of Li_(2)O.Our study provides important understanding of the electrochemistry of the LiO_(2) nanobatteries,which will aid the development of high-performance Li-O_(2) batteries for energy storage applications.

Modeling the dynamics of COVID-19 with carrier effect and environmental contamination

Nowadays,coronavirus disease 2019(COVID-19)poses a major threat to humanity which is caused by a novel coronavirus in Wuhan,China,at the end of December 2019.This novel coronavirus named the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)according to the International Committee on Taxonomy of Viruses(ICTV).It spreads directly through close contact with an asymptomatic(carrier)or symptomatic person who is coughing,sneezing,talking,singing and kissing.It also spreads indirectly through contact with an environment contaminated by viral particles of SARS-COV-2.In the absence of effective treatment against COVID-19,awareness can play an important role in reducing cases of COVID-19.In this study,we develop a mathematical model to better describe the dynamics of COVID-19 by taking into account the above modes of transmission and the prosocial awareness.The existence,uniqueness,positivity and boundedness of solutions of the model are discussed.All possible equilibrium points are determined.The local asymptotic stability of these equilibrium points is studied.Suitable Lyapunov functionals are constructed to investigate the global dynamics of the model.

In situ TEM visualization of Ag catalysis in Li-O_(2)nanobatteries

Lithium-oxygen(Li-O_(2))batteries have been considered as an ideal solution to solving the global energy crisis.Silver(Ag)and Agbased catalyst have been extensively studied due to their high catalytic activities in Li-O_(2)batteries.However,it remains a challenge to track the catalytic mechanism during the charge/discharge process.Here,a nanoscale processing method was used to assemble a Li-O_(2)nanobattery in an aberration-corrected environmental transmission electron microscope(ETEM),where a single Ag nanowire(NW)was used as catalyst for O_(2)electrode.A visualization of the lithium ion insertion process during the electrochemical reactions was achieved in this nanobattery.Numerous Ag nanoparticles(NPs)were observed on the surface of the Ag NW,which were covered by the discharge product Li2O_(2).By simultaneously studying the evolution of the interface and the phase transformation,it can be concluded that these Ag NPs wrapped around Ag NW acted as catalyst during the subsequent charge/discharge reaction.Based on these studies,Ag NPs decorated on porous carbon were synthesized,it can simultaneously improve the cycling stability(100 cycles)and the maximum specific capacity(17,371 mAh·g^(−1)at a current density of 100 mA·g^(−1))in a coin cell Li-O_(2)battery.This study suggests that nanoscale Ag may be a promising catalyst for Li-O_(2)battery.

In situ observation of cracking and self-healing of solid electrolyte interphases during lithium deposition

The growth of lithium(Li)whiskers is detrimental to Li batteries.However,it remains a challenge to directly track Li whisker growth.Here we report in situ observations of electrochemically induced Li deposition under a CO_(2) atmosphere inside an environmental transmission electron microscope.We find that the morphology of individual Li deposits is strongly influenced by the competing processes of cracking and self-healing of the solid electrolyte interphase(SEI).When cracking overwhelms self-healing,the directional growth of Li whiskers predominates.In contrast,when self-healing dominates over cracking,the isotropic growth of round Li particles prevails.The Li deposition rate and SEI constituent can be tuned to control the Li morphologies.We reveal a new“weak-spot”mode of Li dendrite growth,which is attributed to the operation of the Bardeen-Herring growth mechanism in the whisker’s cross section.This work has implications for the control of Li dendrite growth in Li batteries.

In Situ TEM Observation of the Gasification and Growth of Carbon Nanotubes Using Iron Catalysts

We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.

Carbon-Involved Near-Surface Evolution of Cobalt Nanocatalysts:An in Situ Study

When carbon-containing species are involved in reactions catalyzed by transition metals at high temperature,the diffusion of carbon on or in catalysts dramatically influences the catalytic performance.Acquiring information on the carbon-diffusioninvolved evolution of catalysts at the atomic level is crucial for understanding the reaction mechanism yet also challenging.For the chemical vapor deposition process of single-walled carbon nanotubes(SWCNTs),we recorded in situ the catalyst state(solid and molten)composition as well as near-surface structural and chemical evolution at the cobalt catalyst-tube interface with carbon permeation using aberration-corrected environmental transmission electron microscopy and synchrotron X-ray absorption spectroscopy.The nucleation of SWCNTs was linked with an alternating dissolving and precipitating cycle of carbon in catalysts close to the nucleation site.Understanding the dynamics of carbon atoms in catalysts brings deeper insight into the growth mechanism of SWCNTs and facilitates inferring mechanisms of other reactions.The methodologies developed here will find broad applications in studying catalytic and other processes.