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.

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.

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.

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.

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.

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.

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.