Spherical Aberration-corrected Transmission Electron Research Articles

Improvement of chemical mechanical polishing performance by introducing N–Si bond via external coating of cerium oxide with ZIF-8

Cerium oxide (CeO2) nanoparticles are widely used as abrasives in chemical mechanical polishing (CMP), an essential process for obtaining Si wafers with excellent surface quality. While CeO2 nanoparticles form Ce–O–Si bonds, which exhibit good CMP performance, their low activity results in a low removal rate. To address this issue, a two-step ultrasonic dispersion method was employed to prepare a uniform nuclear@shell CeO2@ZIF-8. The process of chemical bond generation in CMP was studied using spherical aberration-corrected transmission electron microscopy and X-ray photoelectron spectroscopy. In comparison to pure cerium oxide, the formation of Ce–O–Si bond was observed, and notably, the emergence of N–Si bond originating from the N of the ZIF-8 shell was identified. Coupled with the increased Ce3+ content, these developments enhanced CMP performance. The material removal rate (MRR) of the CeO2@ZIF-8 abrasives was 151.507 nm/min, which is 89.72 % higher than that of the pure CeO2 abrasives. Moreover, the surface roughness, as determined via AFM testing, was reduced to 0.231 nm within the confines of a 5.0 × 5.0 μm² region. Therefore, this study introduces a novel concept for CMP research by developing a CeO2@ZIF-8 compound abrasive to create a new N–Si bond.

Microstructural study on in-situ high-entropy (NbMoTaWV)C reinforced nanocrystalline NbMoTaWVC refractory high entropy alloys prepared by mechanically alloying

Refractory high-entropy alloys (RHEAs) can be commonly regarded as the best candidates for potentially substituting for the nickel-based superalloys practically used in the areas of aviation and nuclear industry, which can significantly endure in high-temperature and harsh environment. In this work, a nanocrystalline NbMoTaWVC RHEA is successfully produced by mechanical alloying method and X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and spherical aberration corrected transmission electron microscopy (AC-TEM) are employed to systematically characterized the microstructural details of NbMoTaWV and NbMoTaWVC RHEAs mechanically alloyed powders. Our results can support the evidence that the observable minimum nanoparticle sizes of the NbMoTaWV and NbMoTaWVC RHEAs considerably decrease to approximately ∼100 nm. Furthermore, the average grain sizes are gradually refined and thus notably drop to around of 30–50 nm, and five elemental powders can be found to be homogeneously alloyed. The evidence can be confirmed that the order of solid solution may be proposed as follows: Nb → Mo → V → Ta → W. The chemical short-range order occurred at the local nanoscale of NbMoTaWV and NbMoTaWVC RHEAs. Meanwhile, further microstrutural analysis can demonstrate that NbMoTaWV and NbMoTaWVC RHEAs powders with ultrafined grain have a bcc phase structure and bcc + bct matrix phases combined with high-entropy tungsten carbides (NbMoTaWV)C and (NbMoTaWV)2C of nano-precipitated phases, respectively, suggesting that the martensitic transformation probably occurred. The NbMoTaWV and NbMoTaWVC RHEAs powders of locally crystal lattice distortion rates reached approximately 8.07% and 6.33%.

Hybrid additive manufacturing of aluminum matrix composites with improved mechanical properties compared to extruded counterparts

Great difficulties existed in fabricating large components of SiC particles reinforced aluminum matrix composites with excellent mechanical properties using existing manufacturing procedures. This study demonstrated that the challenges can be addressed by developing a hybrid solid-state additive manufacturing method. The influence of the deposition procedures and the post-processing heat treatment on the microstructure and mechanical properties of the SiC particles reinforced 2009 aluminum ally matrix composites (SiCp/2009Al composites) was systematically investigated using advanced technologies such as spherical aberration corrected transmission electron microscope, atom probe tomography, etc. The results showed that the SiCp/2009Al composites produced by the hybrid solid-state additive manufacturing exhibited enhanced tensile properties and improved isotropy in mechanical properties compared to the extruded feedstock of SiCp/2009Al composites. This was attributed to the formation of dense metal with uniformly distributed SiC particles, high-density of Cu–Mg co-clusters, refined grains and SiC particles, low deformation texture, tightly bonded SiCp/2009Al interface, and sound interfacial bonding between deposited layers.

Influence of interface on the domain polarization orientation in ferroelectric Hf0.5Zr0·5O2 thin films

Ferroelectric HfO2-based materials have attracted extensive attention in the research of next-generation nonvolatile memories and logic devices due to their superior scaling properties and compatibility with the CMOS process. However, forming the ferroelectric metastable phase in the thin films of a few nanometers requires clamping of the top and bottom electrodes. As a result, the interface can significantly impact domain structure and polarization, leading to imprinting effects and non-uniform space charge distribution. Here, we have demonstrated how the interface affects the ferroelectric polarization in Hf0.5Zr0·5O2 (HZO) thin films produced by ALD and the physical mechanisms behind it. We found that by regulating the quantity of oxygen vacancy content at the top and bottom interfaces of TiN/HZO/TiN ferroelectric capacitors, it is possible to achieve inversion of polarization orientation. By using a spherical aberration-corrected transmission electron microscope and first-principles calculation, we identified that the internal electric field generated by the accumulation of oxygen vacancies at an interface and the asymmetrical electrostatic energy of the interfacial T-phase layer jointly play a role in the ferroelectric polarization orientation. Our results will significantly help the interface engineering of HfO2-based ferroelectric thin films and devices.

Texture in atomic layer deposited Hf0.5Zr0.5O2 ferroelectric thin films

HfO2-based ferroelectric materials have excellent CMOS compatibility and polarization even in ultrathin films, which is regarded as promising candidate material for memory devices and related electronic devices. However, as the ferroelectric layer thickness scaling down, the consistency of device performance is inevitably affected by the complex polyphase and polycrystalline nature of HfO2-based ferroelectric thin films. Therefore, obtaining and controlling the texture of HfO2-based ferroelectric thin films is extremely important for regulating polarization orientation and improving ferroelectric polarization. In this work, 10 nm Hf0.5Zr0.5O2 (HZO) films were prepared by atomic layer deposition (ALD) on Nb-doped SrTiO3 (NSTO) single crystal substrates. The texture and orientation of HZO films were analyzed through the state-of-the-art spherical aberration corrected transmission electron microscope (Cs-TEM) technique. The domain matching epitaxy between HZO films and NSTO substrate helps eliminate lattice mismatch and residual misfit strain, and ultimately leads to the formation of <112> texture in HZO ferroelectric films. The obtained results represent lattice and interface play an extremely important role in regulating the ferroelectricity of HfO2-based films, which provides a way to design ultra-thin HfO2-based materials with excellent ferroelectric polarization by controlling the crystal structure and orientation.

Rapid Plasma Electrolytic Oxidation Synthesis of Intermetallic PtBi/MgO/Mg Monolithic Catalyst for Efficient Removal of Organic Pollutants.

The intermetallic PtBi/MgO/Mg monolithic catalyst was first prepared using non-equilibrium plasma electrolytic oxidation (PEO) technology. Spherical aberration-corrected transmission electron microscope (ACTEM) observation confirms the successful synthesis of the PtBi intermetallic structure. The efficiency of PtBi/Mg/MgO catalysts in catalyzing the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH4 was demonstrated. The activity factor for the catalyst is 31.8 s-1 g-1, which is much higher than reported values. In addition, the resultant catalyst also exhibits excellent catalytic activity in the organic pollutant reaction of p-nitrobenzoic acid (p-NBA) and methyl orange (MO). Moreover, benefiting from ordered atomic structures and the half-embedded PtBi nanoparticles (NPs), the catalyst demonstrates excellent stability and reproducibility in the degradation of 4-NP. This study provides an example of a simple method for the preparation of intermetallic structures as catalysts for organic pollutant degradation.

Phase transformations in single-layer MoTe2 stimulated by electron irradiation and annealing

Among two-dimensional (2D) transition metal dichalcogenides (TMDs), MoTe2 is predestined for phase-engineering applications due to the small difference in free energy between the semiconducting H-phase and metallic 1T′-phase. At the same time, the complete picture of the phase evolution originating from point defects in single-layer of semiconducting H-MoTe2 via Mo6Te6 nanowires to cubic molybdenum has not yet been reported so far, and it is the topic of the present study. The occurring phase transformations in single-layer H-MoTe2 were initiated by 40–80 kV electrons in the spherical and chromatic aberration-corrected high-resolution transmission electron microscope and/or when subjected to high temperatures. We analyse the damage cross-section at voltages between 40 kV and 80 kV and relate the results to previously published values for other TMDs. Then we demonstrate that electron beam irradiation offers a route to locally transform freestanding single-layer H-MoTe2 into one-dimensional (1D) Mo6Te6 nanowires. Combining the experimental data with the results of first-principles calculations, we explain the transformations in MoTe2 single-layers and Mo6Te6 nanowires by an interplay of electron-beam-induced energy transfer, atom ejection, and oxygen absorption. Further, the effects emerging from electron irradiation are compared with those produced by in situ annealing in a vacuum until pure molybdenum crystals are obtained at temperatures of about 1000 °C. A detailed understanding of high-temperature solid-to-solid phase transformation in the 2D limit can provide insights into the applicability of this material for future device fabrication.

Facile synthesis of Zn0.5Cd0.5S nanosheets with tunable S vacancies for highly efficient photocatalytic hydrogen evolution.

In order to effectively improve the separation efficiency of photogenerated charge carriers and thus the photocatalytic activity, in this work, porous Zn0.5Cd0.5S nanosheets with a controlled amount of S vacancies were prepared by a multistep chemical transformation strategy using the inorganic-organic hybrid ZnS-ethylenediamine (denoted as ZnS(en)0.5) as a hard template. The amount of S vacancies and the morphology of the Zn0.5Cd0.5S nanostructures were tailored by adjusting the hydrolysis time. Furthermore, we report the observation of S vacancies in porous Zn0.5Cd0.5S nanosheets at the atomic level using spherical aberration-corrected (Cs-aberrated) transmission electron microscopy (Cs-corrected-TEM). The results revealed that Zn0.5Cd0.5S nanosheets with S vacancies absorb more visible light and generate more electron-hole carriers due to their porous nanosheet structure. At the same time, sulfur vacancies are introduced into the Zn0.5Cd0.5S nanosheets to capture the electrons generated by the light and further extend the lifetime of the carriers. As expected, the photocatalytic activity of Zn0.5Cd0.5S nanosheets prepared by 4 h hydrolysis is 20.5 times higher than that of Zn0.5Cd0.5S(en)x intermediates. Moreover, Zn0.5Cd0.5S-4h showed excellent cycling stability. This work provides a new strategy for the optimization of Zn0.5Cd0.5S photocatalysts to improve photocatalytic hydrogen evolution.

Enhanced catalytic oxidation of benzene though the synergistic Pt-Ni bimetallic single-atom catalyst

Excellent catalysts for the catalytic oxidation of benzene (C6H6) require active sites with robust oxidation capabilities. Heteronuclear dual-single atom catalysts can exhibit enhanced catalytic activity through synergistic interactions between the dual single atoms (SAs). Herein, we successfully engineered a bimetallic single-atom catalyst, Pt1-Ni1/TiO2-NW, which demonstrates exceptional performance in C6H6 oxidation. Various technologies, including X-ray absorption fine structure and Z-type spherical aberration-corrected transmission electron microscopy, were used to identify the bimetallic single atoms within the catalyst. The catalytic oxidation of C6H6 by Pt1-Ni1/TiO2-NW was comprehensively investigated. Finally, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) were employed to reveal the underlying mechanism for the synergetic effect of the bimetallic single atoms. The results indicate that the introduction of Ni SA favors the formation of Pt SA. The T90% of Pt1-Ni1/TiO2-NW reached 185 °C, a remarkable 40 °C lower than that of the single-atom catalyst Pt1/TiO2-NW. More importantly, the active center of Pt-O-Ni, formed by the collaboration of Pt SA and Ni SA with bridging oxygen, plays a crucial role in reducing the energy barrier during the conversion of C6H6 to phenol and further to benzoquinones. This research provides a valuable methodology for constructing heteronuclear bimetallic single-atom catalysts tailed specifically for C6H6 oxidation.

Cu@Co with Dilatation Strain for High-Performance Electrocatalytic Reduction of Low-Concentration Nitric Oxide.

Electrocatalytic reduction of nitric oxide (NO) to ammonia (NH3 ) is a clean and sustainable strategy to simultaneously remove NO and synthesize NH3 . However, the conversion of low concentration NO to NH3 is still a huge challenge. In this work, the dilatation strain between Cu and Co interface over Cu@Co catalyst is built up and investigated for electroreduction of low concentration NO (volume ratio of 1%) to NH3 . The catalyst shows a high NH3 yield of 627.20µg h-1 cm-2 and a Faradaic efficiency of 76.54%. Through the combination of spherical aberration-corrected transmission electron microscopy and geometric phase analyses, it shows that Co atoms occupy Cu lattice sites to form dilatation strain in the xy direction within Co region. Further density functional theory calculations and NO temperature-programmed desorption (NO-TPD) results show that the surface dilatation strain on Cu@Co is helpful to enhance the NO adsorption and reduce energy barrier of the rate-determining step (*NO to *NOH), thereby accelerating the catalytic reaction. To simultaneously realize NO exhaust gas removal, NH3 green synthesis, and electricity output, a Zn-NO battery with Cu@Co cathode is assembled with a power density of 3.08mW cm-2 and an NH3 yield of 273.37µg h-1 cm-2 .

Microstructure evolution of a Cr-Cr/Mo coated Zr alloys in inert gas and steam environment at high temperature

The Cr/Mo multilayer coating was applied as a diffusion barrier for Cr-coated Zr alloys. The barrier effect and eutectic resistance of the Cr/Mo multilayer were evaluated by annealing the samples up to 1400 °C in an inert gas and steam environment. The microstructure at the interface between the Cr/Mo multilayer and Zr substrate was analyzed by spherical aberration corrected transmission electron microscope (AC-TEM). After high temperature annealing, an interlayer composed of Cr-Mo-Zr mixed phases formed between the coating and Zr substrate. The atomic-resolution EDS revealed that the proportion of Cr, Mo, and Zr in the interlayer was 4:2:3. The growth of the Cr-Mo-Zr interlayer obeyed a parabolic law. The consumption rate of the outer Cr coating was compared to that of Cr coated Zr alloy samples without a Cr/Mo barrier layer. Results show that the Cr/Mo interlayer successfully reduced the Cr-Zr inter-diffusion and eutectic reaction.

Atomic insight into the BEOL thermal budget on phase transition of phase change memory cells

Research works on phase change random access memory (PCRAM) based on Ge–Sb–Te (GST) phase change materials have achieved exciting progress, but the industrialization of PCRAM still faces big challenges, including unsatisfied endurance property or unexpected cell structure failure during fabrication. Here, we investigate the impact of the thermal budget in back-end-of-line (BEOL) process on the microstructure evolution of carbon doped GST (CGST) cells. We demonstrate that the as-deposited amorphous CGST in the confined memory cell will transform to face centered-cubic (FCC) phase with uniform grain size during high temperature up to 400 °C in the BEOL process. However, if there is much more unexpected thermal budget during the BEOL process, the FCC-CGST grains will further grow and transform to highly ⟨0001⟩ oriented single crystalline hexagonal (HEX) GST, together with the formation of voids, leading to the structure failure of the storage cells. By virtue of the advanced spherical aberration corrected transmission electron microscopy (Cs-TEM), we find that there are randomly stacked seven-layered and nine-layered atomic arrangements in single crystalline HEX-GST, corresponding to the chemical stoichiometry of Ge2Sb2Te5 and Ge1Sb2Te4, respectively. Interestingly, twin crystal with the coexistence of vacancy-ordered FCC-GST and HEX-GST on the different twin boundary is observed, indicating that the twin crystals play a critical role in the coalescence and the growth of FCC-GST. This work not only sheds light on the structure failure mechanism of GST cell but also provided additional insight into the formation of HEX-phase in a confined GST memory cell.

Study on the preparation of ceramic membrane support and its Fe migration rule by high‐aluminum fly ash as raw material

AbstractIn order to reduce the cost of ceramic membrane support, ceramic membrane support was prepared using high‐aluminum fly ash as raw material, and its Fe migration rules during the preparation process are studied. The effects of sintering temperature, pore forming agent content, and binder content on the properties of support, such as porosity, pore size, bending strength and water flux have been investigated. The optimum contents of high‐aluminum fly ash, pore forming agent and binder in the ceramic membrane support are 95%, 4%, and 1% respectively, and its sintering temperature is 1300°C. The porosity, bending strength, pore size, and water flux of the prepared support are 37%, 22 MPa, 665 nm, and 2800 L/h·m2·MPa, respectively. X‐ray powder diffractometer, X‐ray fluorescence spectrometer, X‐ray photoelectron spectrometer, inductively coupled plasma spectrometer, transmission electron microscope, spherical aberration corrected transmission electron microscopy, and laser Raman spectroscopy were used to characterize the support and Fe existing morphology in it. The results show that the main phases of sintered support are mullite, corundum, and silica. Massive mullite is produced when the sintering temperature reaches 1200°C. The content of mullite increases with increasing sintering temperature. About 7.7 % content of total Fe in the support exists in the form of Fe2O3. About 92.3% content of total Fe is dissolved into mullite. Fe is evenly distributed in mullite, and it is enriched at the grain boundary by element segregation. Fe in mullite is difficult to dissolve under strong acid conditions, so its stability is very strong.

Engineering Sub-Nanometer Hafnia-Based Ferroelectrics to Break the Scaling Relation for High-Efficiency Piezocatalytic Water Splitting.

Reversible control of ferroelectric polarization is essential to overcome the heterocatalytic kinetic limitation. This can be achieved by creating a surface with switchable electron density; however, owing to the rigidity of traditional ferroelectric oxides, achieving polarization reversal in piezocatalytic processes remains challenging. Herein, sub-nanometer-sized Hf0.5 Zr0.5 O2 (HZO) nanowires with a polymer-like flexibility are synthesized. Oxygen K-edge X-ray absorption spectroscopy and negative spherical aberration-corrected transmission electron microscopy reveal an orthorhombic (Pca21 ) ferroelectric phase of the HZO sub-nanometer wires (SNWs). The ferroelectric polarization of the flexible HZO SNWs can be easily switched by slight external vibration, resulting in dynamic modulation of the binding energy of adsorbates and thus breaking the "scaling relationship" during piezocatalysis. Consequently, the as-synthesized ultrathin HZO nanowires display superb water-splitting activity, with H2 production rate of 25687µmolg-1 h-1 under 40kHz ultrasonic vibration, which is 235and 41times higher than those of non-ferroelectric hafnium oxides and rigid BaTiO3 nanoparticles, respectively. More strikingly, the hydrogen production rates can reach 5.2µmolg-1 h-1 by addition of stirring exclusively.

Triethylenediamine cobalt complex encapsulated in a metal–organic framework cage to prepare a cobalt single-atom catalyst with a high Co-N4 density for an efficient oxygen reduction reaction

Transition metal single atom catalysts (TM SACs) are the most promising oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs) and metal-air batteries. However, the low density of M-Nx active sites seriously hinders further improvement of the ORR electrocatalytic activity. Here, a strategy for encapsulating nitrogen-rich guest molecules (triethylenediamine cobalt complex, [Co(en)3]3+) was proposed to construct a high-performance cobalt single-atom catalyst (Co-encapsulated SAC/NC). With this strategy, the guest molecules are encapsulated into metal–organic framework (MOF) cages as an additional cobalt source to boost cobalt loading, while abundant nitrogen from guest molecules contributes to the formation of Co-N4 active sites. Remarkably, the resulting Co-encapsulated SAC/NC has a high cobalt loading amount of 4.03 wt%, and spherical aberration-corrected transmission electron microscopy (AC-TEM) has confirmed that most cobalt exists in a single-atom state. As a result, the Co-encapsulated SAC/NC exhibits excellent ORR catalytic performance with a half-wave potential of 0.88 V. Furthermore, Zn-air batteries employing Co-encapsulated SAC/NC as air cathode show high peak power density and excellent cycling stability. Density functional theory (DFT) calculations reveal that adjacent active sites have different rate-determining steps and lower reaction energy barriers than a single active site.

In situ observation of two-step crystallization of amorphous oxides via electron microscopy

The transformation from amorphous materials to crystals and the corresponding microscopic mechanism have become a research focus in materials science, condensed matter physics, and biophysics etc. In this paper, taking Y3Al5O12 (YAG) as an example, the crystallization process of amorphous YAG oxide is investigated from an atomic point of view through the combination of spherical aberration-corrected transmission electron microscopy (SCTEM) with an in situ heating method, and the morphology and structural evolution of the surface and interface are explored. It is observed that the crystallization proceeds on the surface and interior of the amorphous YAG separately. Through atomic-scale imaging, it is determined that semi-ordered structures are formed in a few atomic layers at the amorphous/crystalline interface and that the structural transformation process from the amorphous to the semi-ordered state and then to the crystal structure may be the main reason for the multiple stages of the crystallization of amorphous oxides. This study demonstrates the mechanism of the amorphous-to-crystal transformation on the atomic scale and contributes to gaining a better understanding of the crystallization process of bulk oxides, especially complex metal oxides.

Direct atomic-scale visualization of the 90° domain walls and their migrations in Hf0.5Zr0.5O2 ferroelectric thin films

Domain walls (DWs) play an essential role in altering the polarization and related properties of ferroelectric materials, and are regulated by the mechanism of changing atomic configuration. However, compared with perovskite ferroelectrics, the DWs in hafnia-based fluorite-structure ferroelectric is experimentally lacking, especially with regard to detailed studies of atomic-scale structures. The present work used spherical aberration-corrected transmission electron microscope combined with in-situ technique to ascertain the origin, atomic arrangements of 90° DWs in Hf0.5Zr0.5O2 thin films. Different types of 90° DWs were found to exhibit varying migration behaviors in response to the concentration of oxygen vacancies. Point defects and corresponding changes in the local strain field are proposed to drive DW switching in this material. These new insights into the atomic-scale characteristics of 90° DWs are expected to assist in elucidating the structure of DWs and improve our understanding of the ferroelectric characteristics of new type hafnia-based materials.

Interaction mechanism between immiscible Fe-Mg element diffusion and crystal defect annihilation in the steel/Mg composite interface region

Crystal defect-induced elemental diffusion between immiscible metals is the key to achieve metallurgical bonding. However, the interaction between immiscible element diffusion and crystal defect annihilation is unclear. In this paper, in-situ heat treatment experiments were conducted at the steel/Mg composite interface by ambient atmosphere spherical aberration corrected transmission electron microscope. The immiscible element diffusion phenomenon and crystal defect annihilation phenomenon in the composite interface region were studied, and the interaction mechanism was revealed. The results show that during the heat treatment, the diffusion of Mg element to the steel side is obvious, while the diffusion of Fe element to the Mg side is not obvious, which is called “one-way selective diffusion effect”. The annihilation rate of steel crystal defects is much smaller than that of Mg. The stable crystal defects of steel in the interface region can provide a channel for Mg elements diffusion, while the faster annihilation rate of Mg crystal defects causes Fe elements to hardly diffuse into Mg. The Mg elements that have diffused into the steel side have a pinning effect on dislocations and grain boundary movement, which in turn increases the thermal stability of the steel crystal defects. This study provides theoretical guidance for promoting the element diffusion at the immiscible metals composite interface.

Guanosine-derived atomically dispersed Cu-N3-C sites for efficient electroreduction of carbon dioxide

Single-atom copper (Cu) embedded within carbon catalysts have demonstrated significant potential in the electrochemical reduction of carbon dioxide (CO2) into valuable chemicals and fuels. Herein, we develop a straightforward and template-free strategy for synthesizing atomically dispersed CuNC catalysts (CuG) by annealing the self-assembled guanosine. The CuG catalysts display two-dimensional morphology, tunable pore size and large surface areas that can be adjusted by changing carbonization temperature. Spherical aberration-corrected transmission electron microscopy reveals that single-atom Cu are homogeneously dispersed on the surface of carbon nanosheets. The optimum CuG-1000 catalysts achieve a high CO Faradaic efficiency (FEco) up to 99% and a high CO current density of 6.53 mA cm−2 (−0.65 V vs. RHE). Besides, the flow cell test of CuG-1000 shows a high current density up to 25.2 mA cm−2 and the FEco still exceeded 91% after more than 20 h of testing. Specifically, the existence of Cu-N3-C active sites was proved by extended X-ray absorption fine structure (EXAFS). Density functional theory evidences that tricoordinated copper with N can largely regulate the adsorption and desorption of key intermediates by transferring electrons to *COOH through Cu atoms, thereby improving selectivity toward CO. This work demonstrates the active origin of CuNC catalysts in CO2 electroreduction and offers a blueprint to construct atomically dispersed transition site catalysts by supramolecular self-assembly strategy.

Recognizing the formation of single-atom vanadium by enthalpy and its advantage in selective catalytic reduction of nitrogen oxide

Developing a more effective catalyst for the environmental pollutant is always the pursuit of worldwide researchers. In previous reports, most works were focused on prepared catalysts, and more efforts should explore process from a precursor to the formed catalyst. In this work, V supported TiO2 catalysts were synthesized with different V loadings, and compared in selective catalytic reduction of nitrogen oxide. For the first time, differential scanning calorimetry was used to analyze the forming enthalpy for these catalysts. As a result, turnover frequency (TOF) was decreased from 0.05 to 0.001 s−1 when the loading was increased from 0.05 to 15 mol%. At the same time, the forming enthalpy was decreased from 16.53 to 1.80 KJ·mol−1. Spherical Aberration Corrected Transmission Electron Microscope recognized both single-atom and cluster V even at the lowest loading. What’s more, density functional theory revealed that single-atom V had a lower dehydrogenation energy (1.088–1.152 eV) than cluster V during the catalysis (1.834–1.850 eV). According to these evidences, single-atom V had bigger formation enthalpy, lower dehydrogenation energy, and larger TOF than cluster V. These results help to optimize the preparation process for an effective catalyst, which is in favor of hazardous-pollutant treatment.