Atomic Resolution Study of Reversible Conversion Reaction in Metal Oxide Electrodes for Lithium-Ion Battery

Electrode materials based on conversion reactions with lithium ions have shown much higher energy density than those based on intercalation reactions. Here, nanocubes of a typical metal oxide (Co₃O₄) were grown on few-layer graphene, and their electrochemical lithiation and delithiation were investigated at atomic resolution by <i>in situ</i> transmission electron microscopy to reveal the mechanism of the reversible conversion reaction. During lithiation, a lithium-inserted Co₃O₄ phase and a phase consisting of nanosized Co–Li–O clusters are identified as the intermediate products prior to the subsequent formation of Li₂O crystals. In delithiation, the reduced metal nanoparticles form a network and breakdown into even smaller clusters that act as catalysts to prompt reduction of Li₂O, and CoO nanoparticles are identified as the product of the deconversion reaction. Such direct real-space, real-time atomic-scale observations shed light on the phenomena and mechanisms in reaction-based electrochemical energy conversion and provide impetus for further development in electrochemical charge storage devices

Size-Controlled Intercalation-to-Conversion Transition in Lithiation of Transition-Metal ChalcogenidesNbSe₃

Transition-metal chalcogenides (TMCs) can be used either as intercalation cathodes or as conversion-type anodes for lithium ion batteries, for which two distinctively different lithiation reaction mechanisms govern the electrochemical performance of TMCs. However, the factors that control the transition of lithiation mechanisms remain elusive. In this work, we investigated the lithiation process of NbSe₃ ribbons using <i>in situ</i> transmission electron microscopy and observed a size-dependent transition from intercalation to the conversion reaction. Large NbSe₃ ribbons can accommodate high concentrations of Li⁺ through intercalation by relaxing their internal spacing, while lithiation of small NbSe₃ ribbons proceeds readily to full conversion. We found that the size-dependent variation of the lithiation mechanism is associated with both Li⁺ diffusion in NbSe₃ and the accommodation of newly formed phases. For large NbSe₃ ribbons, the intercalation-to-conversion transition is impeded by both long-range Li⁺ diffusion and large-scale accommodation of volume expansion induced by the formation of new phases. These results demonstrate the inherent structural instability of NbSe₃ as an intercalation cathode and its high lithiation rate as a promising conversion-type anode

Structural Evolution of Cu/ZnO Catalysts during Water-Gas Shift Reaction: An <i>In Situ</i> Transmission Electron Microscopy Study

Supported metal catalysts experience significant structural evolution during the activation process and reaction conditions, which is critical to achieve a desired active surface and interface enabling efficient catalytic processes. However, such dynamic structural information and related mechanistic understandings remain largely elusive owing to the limitation of real-time capturing dynamic information under reaction conditions. Here, using in situ environment transmission electron microscopy, we demonstrate the atomic-scale structural evolution of the model Cu/ZnO catalyst under relevant water-gas shift reaction (WGSR) conditions. Under a CO gas environment, Cu nanoparticles decompose into smaller Cu species and redistribute on ZnO supports with either the crystalline Cu2O or amorphous CuOx phase due to a strong CO–Cu interaction. In addition, we visualize various metal–support interactions between Cu and ZnO under reaction conditions, e.g., ZnO clusters precipitating on Cu nanoparticles, which are critical to understand active sites of Cu/ZnO as catalysts for WGSR. These in situ atomic-scale observations highlight the dynamic interplays between Cu and ZnO that can be extended to other supported metal catalysts

Structural Evolution of Cu/ZnO Catalysts during Water-Gas Shift Reaction: An <i>In Situ</i> Transmission Electron Microscopy Study

Supported metal catalysts experience significant structural evolution during the activation process and reaction conditions, which is critical to achieve a desired active surface and interface enabling efficient catalytic processes. However, such dynamic structural information and related mechanistic understandings remain largely elusive owing to the limitation of real-time capturing dynamic information under reaction conditions. Here, using in situ environment transmission electron microscopy, we demonstrate the atomic-scale structural evolution of the model Cu/ZnO catalyst under relevant water-gas shift reaction (WGSR) conditions. Under a CO gas environment, Cu nanoparticles decompose into smaller Cu species and redistribute on ZnO supports with either the crystalline Cu2O or amorphous CuOx phase due to a strong CO–Cu interaction. In addition, we visualize various metal–support interactions between Cu and ZnO under reaction conditions, e.g., ZnO clusters precipitating on Cu nanoparticles, which are critical to understand active sites of Cu/ZnO as catalysts for WGSR. These in situ atomic-scale observations highlight the dynamic interplays between Cu and ZnO that can be extended to other supported metal catalysts

Structural Evolution of Cu/ZnO Catalysts during Water-Gas Shift Reaction: An <i>In Situ</i> Transmission Electron Microscopy Study

Supported metal catalysts experience significant structural evolution during the activation process and reaction conditions, which is critical to achieve a desired active surface and interface enabling efficient catalytic processes. However, such dynamic structural information and related mechanistic understandings remain largely elusive owing to the limitation of real-time capturing dynamic information under reaction conditions. Here, using in situ environment transmission electron microscopy, we demonstrate the atomic-scale structural evolution of the model Cu/ZnO catalyst under relevant water-gas shift reaction (WGSR) conditions. Under a CO gas environment, Cu nanoparticles decompose into smaller Cu species and redistribute on ZnO supports with either the crystalline Cu2O or amorphous CuOx phase due to a strong CO–Cu interaction. In addition, we visualize various metal–support interactions between Cu and ZnO under reaction conditions, e.g., ZnO clusters precipitating on Cu nanoparticles, which are critical to understand active sites of Cu/ZnO as catalysts for WGSR. These in situ atomic-scale observations highlight the dynamic interplays between Cu and ZnO that can be extended to other supported metal catalysts

In Situ Transmission Electron Microsopy of Oxide Shell-Induced Pore Formation in (De)lithiated Silicon Nanowires

Silicon (Si) nanowires with a silicon oxide (SiOx) shell undergoing lithiation and delithiation were examined by in situ transmission electron microscopy (TEM). Large pores formed in the nanowires during the delithiation cycle. We found that the oxide shell constrains the expansion of the Si nanowires during lithitation and then induces pore formation in the nanowires. We propose that the SiOx shell prevents the vacancies that result from the loss of lithium from escaping the Si core, leading to pore nucleation and growth. It is also possible that the difference in mechanical properties of the expanding and contracting Si nanowire and SiOx shell contribute to the observed pore formation. This in situ study reaffirms the need to directly observe structural changes that occur during cycling in battery materials, especially when modified by coatings

Structural Evolution of Cu/ZnO Catalysts during Water-Gas Shift Reaction: An <i>In Situ</i> Transmission Electron Microscopy Study

Supported metal catalysts experience significant structural evolution during the activation process and reaction conditions, which is critical to achieve a desired active surface and interface enabling efficient catalytic processes. However, such dynamic structural information and related mechanistic understandings remain largely elusive owing to the limitation of real-time capturing dynamic information under reaction conditions. Here, using in situ environment transmission electron microscopy, we demonstrate the atomic-scale structural evolution of the model Cu/ZnO catalyst under relevant water-gas shift reaction (WGSR) conditions. Under a CO gas environment, Cu nanoparticles decompose into smaller Cu species and redistribute on ZnO supports with either the crystalline Cu2O or amorphous CuOx phase due to a strong CO–Cu interaction. In addition, we visualize various metal–support interactions between Cu and ZnO under reaction conditions, e.g., ZnO clusters precipitating on Cu nanoparticles, which are critical to understand active sites of Cu/ZnO as catalysts for WGSR. These in situ atomic-scale observations highlight the dynamic interplays between Cu and ZnO that can be extended to other supported metal catalysts

Probing the Phase Transition during the Formation of Lithium Lanthanum Zirconium Oxide Solid Electrolyte

Lithium lanthanum zirconium oxide (LLZO) has long been considered as a promising solid electrolyte for all-solid-state lithium (Li) metal batteries because of its interfacial stability when coupled with a Li metal anode. However, the cubic phase of LLZO (c-LLZO) with a higher Li-ion conductivity has a complex atomic structure and is subject to complicated phase transition during its processing and working conditions, which remain largely elusive. Here, we reveal the phase transition process during the formation of c-LLZO nanotubes through detailed microscopic characterization by scanning and transmission electron microscopy as well as X-ray diffraction. We find four typical stages during the formation of c-LLZO along with several intermediate phases including lanthanum (La)-rich cubic lanthanum zirconium oxide (La-rich c-LZO), c-LZO, and La-rich c-LLZO. We also reveal the role of m-Li2CO3 and h-Li2O2 as the “phase mediator”

Metal Affinity of Support Dictates Sintering of Gold Catalysts

Sintering during heterogeneous catalytic reactions is one of the most notorious deactivation channels in catalysts of supported metal nanoparticles. It is therefore critical to understand the effect of support on the sintering behavior. Here, by using in situ aberration-corrected transmission electron microscopy and computational modeling, the atomic-scale dynamic interactions are revealed between Au nanoparticles and various supports. It is found that Au nanoparticles on ceria have a smaller contact angle and are apparently less mobile, especially at surface steps when compared with those on the amorphous silica. Analogous to hydrophilicity, we attribute the origin of mobility of small nanoparticles to metal affinity, which determines the interaction between metal and support material. Ab initio molecular dynamics (AIMD) and machine learning-based deep potential molecular dynamics (DPMD) simulations directly capture a coalescence process on the silica surface and the strong pinning of gold on ceria. The joint experimental and theoretical results on the atomic scale demonstrate the metal affinity of active and inert supports as the key descriptor pertinent to sintering and deactivation of heterogeneous catalysts

Metal Affinity of Support Dictates Sintering of Gold Catalysts

Sintering during heterogeneous catalytic reactions is one of the most notorious deactivation channels in catalysts of supported metal nanoparticles. It is therefore critical to understand the effect of support on the sintering behavior. Here, by using in situ aberration-corrected transmission electron microscopy and computational modeling, the atomic-scale dynamic interactions are revealed between Au nanoparticles and various supports. It is found that Au nanoparticles on ceria have a smaller contact angle and are apparently less mobile, especially at surface steps when compared with those on the amorphous silica. Analogous to hydrophilicity, we attribute the origin of mobility of small nanoparticles to metal affinity, which determines the interaction between metal and support material. Ab initio molecular dynamics (AIMD) and machine learning-based deep potential molecular dynamics (DPMD) simulations directly capture a coalescence process on the silica surface and the strong pinning of gold on ceria. The joint experimental and theoretical results on the atomic scale demonstrate the metal affinity of active and inert supports as the key descriptor pertinent to sintering and deactivation of heterogeneous catalysts