High-angle Annular Dark-field Scanning Transmission Electron Microscopy Research Articles

Atomically thin Co-doped nickel oxide/hydroxide superstructure toward high-energy supercapacitors

Atomically thin nanosheets can expose almost all electroactive sites, which deliver outstanding electrochemical performances. However, the direct fabrication of atomically thin nanosheets array on conductive substrates as binder-free electrodes remains a challenge. Herein, atomically thin (ca. 1.4 nm) Co-doped nickel oxide/hydroxide (CoNiOHx) nanosheets superstructure is grown on Ni foam via an alanine-induced in-situ synthesis strategy. High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) verifies the formation of Co8Ni16O32 mesophase between Co-doped Ni(OH)2 and NiO in the optimized sample. Density functional theory (DFT) calculations demonstrate an improved electrical conductivity and low deprotonation energy in Co8Ni16O32, contributing to elevated electrochemical performances. As expected, the electrode delivers a super-high specific capacity of 2244 mC cm−2 (ca. 1268 C g−1) at 2 mA cm−2 and prominent long-life span with no capacity decay after 5000 cycles. Moreover, the asymmetric supercapacitor constructed by coupling the above cathode and activated carbon (AC) anode displays a high energy density of 73.3 Wh kg−1 at the power density of 2250 W kg−1, as well as meritorious cycling stability. This work provides a new strategy for the construction of atomically thin superstructure on conductive metal substrate with high energy storage capability.

Porous CN@MOF derived N, S-doped hierarchical framework carrying Co3Fe7/Fe0.8Co0.2S heterojunction: An efficient bifunctional cathode catalyst for Zn–air battery

The exploiting of bifunctional transition metal electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is of significance for the commercialization of rechargeable zinc-air batteries (ZABs). Herein, the N and S atoms-doped hierarchical carbon framework hosting the Co3Fe7/Fe0.8Co0.2S heterojunction is synthesized by employing porous g-C3N4 as framework and spacer, and FeCo-ZIF as metal source followed by sulfidation and pyrolysis. The detailed characterization confirms that the porous g-C3N4 plays a crucial role in improving the dispersion of metal nanoparticles. The obtained FeCo-Sx@NSC-900 catalysts exhibit layered accumulation configuration with uniformly distributed metal nanoparticles. Moreover, the typical carbon@metal nanoparticles and heterojunction structure can be observed from the HRTEM (High-Resolution Transmission Electron Microscopy) and HAADF-STEM (high-angle annular dark-field STEM) analysis results. The optimal FeCo-Sx@NSC-900 catalysts deliver exceptional ORR and OER performance with a potential difference between ORR and OER of merely 0.713 V, which is superior to the commercial Pt/C+RuO2 catalysts and other monometallic catalysts. Additionally, the ZAB assembled with the optimal FeCo-Sx@NSC-900 catalysts as cathode affords a good battery performance with high OCV (1.50 V), large power density (172 mW/cm2), good discharge stability, large specific capacity, and long-term charge/discharge stability (>300 cycles).

Scanning transmission electron microscopy and atom probe tomography analysis of non-stoichiometry long-period-stacking-ordered structures in Mg-Ni-Y/Sm alloys

The long-period-stacking-ordered (LPSO) structure affects the mechanical, corrosion and hydrolysis properties of Mg alloys. The current work employs high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and atom probe tomography (APT) to investigate the structural and local chemical information of LPSO phases formed in Mg-Ni-Y/Sm ternary alloys after extended isothermal annealing. Depending on the alloying elements and their concentrations, Mg-Ni-Y/Sm develops a two-phase LPSO + α-Mg structure in which the LPSO phase contains defects, hybrid LPSO structure, and Mg insertions. HAADF-STEM and APT indicate non-stoichiometric LPSO with incomplete Ni6(Y/Sm)8 clusters. In addition, the APT quantitatively determines the local composition of LPSO and confirms the presence of Ni within the Mg bonding layers. These results provide insight into a better understanding of the structure and hydrolysis properties of LPSO-Mg alloys.

Growth mechanism of star-shaped Au–Ag nanoparticles synthesized by ascorbic acid reduction and underpotential deposition

The growth mechanism of star-shaped Au–Ag nanoparticles, which is important for improving the absorption efficiency of nanoparticles in the near-infrared region, remains to be clarified. In this study, the growth mechanism by stabilizing certain facets of Au in spines by underpotential deposition of Ag was investigated. The nanoparticles were analyzed primarily by scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy. Analysis of spines on nanoparticles synthesized with an Au/Ag ratio of 18/4 revealed that approximately 1 nm of Ag was deposited on the topmost surface of Au, and the growth direction of spines was <200>. Underpotential deposition of Ag nanolayers on specific facets of the spines on nanoparticles was observed for the first time by elemental mapping and high-angle annular dark-field STEM tomography. These findings are expected to contribute to the morphology control of plasmonic nanoparticles.

Different mechanisms of A-site and B-site high entropy effect on radiation tolerance of pyrochlores

The properties of high entropy pyrochlore have been studied extensively, but there is no consistent conclusion on its radiation tolerance. Besides, the mechanism of the high entropy effect on the radiation tolerance of pyrochlore is still unclear. In this work, combined with experiments and calculations of pyrochlores with similar cationic radius ratios, the A-site and B-site high entropy effects on structural evolution under irradiation are analyzed. In situ irradiation experiments were carried out on A-site high entropy pyrochlores such as (La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7, B-site Gd2(Ti1/3Sn1/3Zr1/3)2O7, and ternary pyrochlore Sm2Zr2O7 and Gd2Sn2O7 for comparison. The A-site high entropy pyrochlore can maintain a stable structure under high fluence irradiation like corresponding ternary pyrochlore, demonstrated by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy dispersive spectroscopy (EDS) mapping and Raman spectrum. The additional irradiation experiments on A-site high entropy pyrochlores (La1/3Nd1/3Gd1/3)2Zr2O7 and (Nd1/3Sm1/3Gd1/3)2Zr2O7 also confirm the similarity under irradiation between A-site high entropy and ternary pyrochlores. However, the B-site high entropy pyrochlore Gd2(Ti1/3Sn1/3Zr1/3)2O7 becomes amorphous at exceptionally low irradiation fluences, indicating a significantly distinct radiation tolerance compared with the A-site high entropy. The difference between the A-site and B-site high entropy effect is analyzed from cationic lattice distortion, bond strength, and inner electron binding energy by first-principles calculations. The results reveal the role and mechanism of the high entropy effect in pyrochlores and lay a foundation for material design and future applications.

Single-atom iridium doped ultrathin MoS2 layers as a highly efficient catalyst for the hydrodeoxygenation of 5-hydroxymethylfurfural

The catalytic transformation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) is of great importance within the context of biomass valorization, but remains a major challenge due to the complicated reaction networks. Herein, single-atom Ir doped ultrathin MoS2 layers were synthesized and used as catalyst for the hydrodeoxygenation of HMF, yielding 96.5% of DMF. The single atomic structure of Ir was determined by X-ray diffraction (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure analysis (XAFS), and X-ray photoelectron spectroscopy (XPS). Furthermore, the Ir doped MoS2 catalyst showed excellent stability and did not deactivate after five reaction cycles. This work expands the applications of single-atom catalysts and introduces a new and highly efficient catalyst for the sustainable production of DMF.

Electrocatalysis of ammonia on NiCu nanoclusters with higher activity and stability synthesized by a simplified polyol technique

This work focuses on a simplified polyol process by which to synthesize five different NiCu/C nanoclusters (NCs) electrocatalysts with the variation of mass and atomic ratio. NCs are characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy, transmission electron spectroscopy (TEM), and scanning electron microscopy with energy-dispersive spectroscopy (EDS) for their crystallite and electronic structures, morphological studies, and elemental composition. The high-angle annular dark-field scanning TEM coupled with EDS elemental mapping has confirmed that nanoparticles (NPs) are formed with Ni and Cu, and NPs are subsequently noted to conform into NCs in such a fashion that NiCu NPs are interconnected to each other rather than overlapping considered a unique distribution of NiCu NCs on the carbon support observed in STEM. NPs arrangement in the conformation of NCs has largely increased in the coverage of NiCu-oxyhydroxides working as active sites for ammonia electrocatalysis evidenced in cyclic voltammograms and XPS investigation. NCs were employed for the oxidation of NH4OH, NH4Cl, NH4NO3, and (NH4)2SO4 of which NiCu/C-2 has shown the highest performance over other NiCu/C samples and their individuals. NiCu/C-2 is also found to have higher stability than other mono/bi-metallic electrocatalysts on the stability test preformed in an electrochemical environment. In addition, the sharp drops of the current in the chronoamperometric curves have been investigated during the stability test.

A novel synthesis from instability difference between SiC 3-C and 6-H crystal to form nanoparticles stems by alkali solution and its degrading various environmental pollutants

In this paper, the nano silicon carbide with different sizes was prepared without hydrofluoric acid by using simple milling and related low temperature etching process in normal pressure. Also, it was the first time verified that 3-C dominated crystalline form of polycrystalline silicon carbide is etched, leaving the 6-H silicon carbide crystalline form by the Raman spectra and HAADF-STEM (high-angle-annular dark-field scanning transmission electron microscopy) imaging that. The application of the alkali etching technique could precise control the partial structural transformation of silicon carbide crystals to a certain extent, which further expands the traditional crystal structure transformation process. In addition, this paper demonstrates the silicon carbide composites in photocatalytic removal of various organic pollutants from aqueous solutions. In the photo degradation of MB (Methylene Blue), the removal rate of the modified silicon carbide shown ten times as much as the commercial silicon carbide. The 1-h degradation efficiency was significantly higher in the 50 μL H2O2 system (100.0%, 86.8% and 89.9% removal of MB, Rhodamine B, Methyl Orange and Tetracycline hydrochloride, respectively). Furthermore, the unit spin concentrations of vacancy defects, superoxide radicals and hydroxyl radicals were quantitatively analyzed. The vacancy defects of the etched material were 1000 times higher than before, and the modified silicon carbide had higher transmittance to infrared and visible light. It strongly absorbs ultraviolet light. Conversely, the research on micron-sized silicon carbide loaded with Ag and Pt atoms found that it had a nitrogen fixation effect during the warming up process, in a nitrogen atmosphere.

Effect of Solution Temperature and Quench Delay on the Microstructure and Mechanical Properties of an Extruded Al-Mg-Si-Cu-Mn alloy

The effect of solution temperature and quench delay on the microstructure and mechanical properties of an extruded Al-Mg-Si-Cu-Mn alloy was investigated by employing differential scanning calorimetry, transmission electron microscopy, hardness test, and tensile test. The extruded specimens were held at 500 and 540 &lt;sup&gt;o&lt;/sup&gt;C, respectively, for 80 min for solutionizing and then immediately quenched in water or exposed to air for 30 sec before water quenching. Each specimen was further heat treated at 180 &lt;sup&gt;o&lt;/sup&gt;C for 6 hr for artificial aging. Quantitative analysis of the precipitates in the artificially aged specimens was performed using high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and fast Fourier transforms (FFT) analysis. Solution treatment at 540 &lt;sup&gt;o&lt;/sup&gt;C led to higher number density of precipitates and higher strengths after artificial aging, compared with solution treatment at 500 &lt;sup&gt;o&lt;/sup&gt;C. Quench delay resulted in a lower number density of precipitates and lower strengths after artificial aging. The specimen solution treated at 540 &lt;sup&gt;o&lt;/sup&gt;C with no quench delay showed the largest peak area of precipitate formation in the differential scanning calorimetry, and concurrently exhibited the highest strengths after artificial aging. Strength reduction by quench delay was higher in the specimen solution treated at 500 &lt;sup&gt;o&lt;/sup&gt;C than that treated at 540 &lt;sup&gt;o&lt;/sup&gt;C; this was consistent with the results of higher reduction in the number density of precipitates.

Selective hydrodeoxygenation of guaiacol to phenol over CoFe/reduced graphene oxide

A reduced graphene oxide (rGO)-supported CoFe bimetallic catalyst (CoFe/rGO) was synthesized and used for hydrodeoxygenation of guaiacol to phenol (Ph). The CoFe/rGO catalyst without reduction pretreatment showed excellent catalytic performance, achieving 94.0 mol% conversion and 70.8 mol% selectivity to Ph at mild reaction temperature and low H2 pressure. The microstructure and chemical composition of the CoFe/rGO catalyst were characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and H2 temperature-programmed reduction (H2-TPR) characterization analysis. Co and Fe are supported on rGO in forms of the isolated metal atoms embedded in the rGO matrix and the CoFe oxide nanoparticles attached on rGO surface. Fe as a promoter weakens the hydrogenation activity of Co to benzene ring and dramatically improves the selectivity to Ph. The unique of rGO on constructing catalytic active sites and the synergistic effect of Co and Fe bimetals make CoFe/rGO an excellent catalyst.

Atom column analysis of (Fe,Cr)2B phase in high B containing ferritic steel

This paper depicts nuances of atomistic level characterization of (Fe,Cr)2B crystal in a high B containing P91 steel using probe aberration-corrected Scanning Transmission Electron Microscope (STEM) based techniques. Substitution of Cr atoms in Fe atom positions resulted in intensity variation of atomic columns of a STEM-High Angle Annular Dark Field (HAADF) image. Image simulation has been used to understand this variation. Relative estimation of Cr atom substitution in Fe atom columns has also been quantified through the analysis of changes in peak profile intensity ratio of STEM-HAADF image in comparison with simulated images. Imaging light atoms, such as B, has recently been made possible with the advent of the Differential Phase Contrast (DPC) detectors. In this work, STEM based Integrated DPC (iDPC) has been used to obtain a very detailed image of the (Fe,Cr)2B crystal showing projection of the Fe/Cr and B atom columns along [100]. However, the observed delocalization of B atom columns was intriguing. Computational analysis using density functional theory (DFT) modelling was employed to understand the effect of Cr substitution on BB bond length with actually little or no effect. Further theoretical calculations confirmed that the energy imparted by the incident electron during imaging was responsible for the B atom delocalization.

Visualization of the structural transformation of NiO/YSZ/BZY nanocomposite particles using in situ gas environmental transmission electron microscopy.

This study focused on investigating the dynamic structural transformations of spherical NiO/YSZ/BZY triple-phase nanocomposite particles, commonly employed for cermet anodes, during the hydrogen reduction reaction. We utilized both spherical aberration (Cs) corrected transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation modes under a controlled gaseous environment. The environmental gas pressure was set to 1 atm (760 Torr), mirroring real-world conditions. To elucidate pre- and post-hydrogen reduction compositional alterations, we conducted elemental mapping using energy-dispersive X-ray spectroscopy (EDS). Our findings indicated that NiO nanoparticles underwent reduction to Ni particles upon heat treatments in an environment containing H2 gas. Significantly, this reduction of NiO led to the migration of Ni along the external surface of each composite particle, ultimately resulting in the agglomeration at the interparticle spaces among the three NiO/YSZ/BZY nanocomposite particles.

Atomically dispersed silver atoms incorporated in spinel cobalt oxide (Co3O4) for boosting oxygen evolution reaction

Incorporating noble metal single atoms into lattice of spinel cobalt oxide (Co3O4) is an attractive way to fabricate oxygen evolution reaction (OER) electrocatalysts because of the high activity and economic benefit. The commonly used high valence noble metal dopants such as ruthenium, iridium and rhodium tend to supersede Co3+ at octahedral site of Co3O4 and result in great activity, the origins of admirable activity were also wildly investigated. However, bare explorations on doping noble metal single atom into tetrahedral site of Co3O4 to construct OER catalyst have been reported, corresponding catalytic activity and mechanism remain mystery. Here, a promising structure that tetrahedrally substituent Ag single atom embedded in Co3O4 nanoparticles on the surface of carbon nanotube (Ag-Co3O4/CNT) was presented, and its performance in OER was probed. The high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption spectroscopy (XAS) demonstrate the successful embeddedness of atomical Ag atom in Co3O4 lattice, the resultant electronic interaction is conducive to promote charge transfer for OER. Theoretical calculations further disclose that atomical Ag dopant prefers to replace tetrahedral Co2+ rather than octahedral Co3+. The substitution Ag acts as the active site through Ag-Co bridge and facilitates the desorption process, which improves the turnover frequency (TOF) and boosts the intrinsic activity of Ag-Co3O4/CNT. Benefiting from the essentials above, Ag-Co3O4/CNT displays remarkable activity (236 mV@10 mA cm−2) and robust stability for alkaline OER. This finding offers a potential direction for the design of noble metal single atom involved Co3O4 based OER electrocatalysts.

In Situ Formation of a LiBO2 Coating Layer and Spinel Phase for Ni-Rich Cathode Materials from a Boric Acid-Etched Precursor.

Ni-rich cathode materials exhibit superior energy densities and have attracted interest among both research and industrial fields; whereas, their practical application is hindered by the intrinsic drawbacks brought by the high nickel content such as structural instability and rapid capacity fading. Herein, in situ formation of a LiBO2 coating layer and spinel phase layer is achieved on the surface of a Ni-rich cathode material via a boric acid etching method at the precursor state. The spinel phase is considered to have a 3D lithium diffusion tunnel and hence faster diffusion kinetics. Moreover, the LiBO2 layer possesses excellent (electro)chemical inertness and can suppress electrolyte decomposition, resulting in a more inorganic and stable cathode-electrolyte interface. The surface reconstructed sample exhibits better cyclic stability (93.3% capacity retention vs 85.3% for the pristine sample at 1 C for 100 cycles) and rate performance. The superiority of this surface reconstruction is demonstrated by a series of electrochemical techniques and characterization methods including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), post-mortem X-ray photoelectron spectroscopy (XPS) analysis, and density functional theory (DFT) calculations.

Single-atom Pd anchored in the porphyrin-center of ultrathin 2D-MOFs as the active center to enhance photocatalytic hydrogen-evolution and NO-removal

Single-atom catalysts were widely used to treat atmospheric pollution and alleviate energy crises through photocatalysis. However, how to prevent the aggregation of single atoms during the preparation and catalytic processes remained a great challenge. Herein, a novel ultrathin two-dimensional porphyrin-based single-atom photocatalyst Ti-MOF (abbreviated as TMPd) obtained through a simple hydrothermal synthesis strategy was used for photocatalytic hydrogen evolution and NO removal, in which the single-atom Pd tightly anchored in the center of porphyrin to ensure single-atom Pd stable existence. Compared with most reported MOFs-based photocatalysts, the TMPd showed an excellent hydrogen evolution rate (1.32 mmol g−1 h−1) and the NO removal efficiency (62%) under visible light irradiation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy (XAFS) proved that pd in TMPd existed in an isolated state, and the atomic force microscope (AFM) proved the ultrathin morphology of TMPd. DFT calculations had demonstrated that single-atom Pd could serve as the active center and more effectively achieve electron transfer, indicating that single-atom Pd played a vital role in photocatalytic hydrogen evolution. In addition, a possible photocatalytic pathway of NO removal was proposed based on ESR and in-situ infrared spectra, in which the catalysts anchored with single-atom Pd could produce more active substances and more effectively oxidize NO to NO2− or NO3−. The results suggested that coordinating single-atom metal species as the active site in the center of porphyrin could be a feasible strategy to obtain various ultrathin porphyrin-based single-atom photocatalysts to acquire excellent photocatalytic performance further.

Fabrication and Characterization of LiNi1/3Mn1/3Co1/3O2/Li0.6La0.4TiO3/Li4Ti5O12 Full Cell All-Solid-State Thin Film Li-Ion Batteries for Energy Applications

Recent days, natural calamities caused by the global warming and climate changes are major concern for the entire globe and there is a pressing need to address such issues to save the mankind from further havoc and devastation. To reduce the carbon emission, countries are shifting dramatically towards renewable sources for their energy needs for their day-to-day life. Li ion batteries are in the forefront of the battle towards the sustainable growth and development due to their high energy density and renewable in nature. In the present case, we report on development of thin film based all-solid-state batteries (ASSB) for energy applications. LiNi1/3Mn1/3Co1/3O2 (NMC), Li0.6La0.4TiO3 (LLTO) and Li4Ti5O12 (LTO) materials are employed as a cathode, solid electrolyte and anode layers for fabricating a full cell all-solid-state thin film batteries. All the layers are fabricated employing RF sputtering technique. Before fabricating the full cell, individual layers are fabricated and their electrochemical and/or ionic conductivity properties are explored. Li0.6La0.4TiO3 solid electrolyte thin films are seen to exhibit room temperature in-plane ionic conductivity in the order of 10-3 S/cm. NMC thin film with the thickness of 100 nm exhibits specific capacity of 91 µAh/cm2 and the redox peaks at 3.8 V and 3.5 V. LTO anode thin films shows the specific capacity close to 100 mAh/cm2and the redox peaks around 1.5 V. XRD pattern of NMC/LLTO/LTO full cell shows the diffraction peaks corresponding to all the three layers. Cross-sectional scanning electron microscope (SEM) image indicates the uniform coating and presence of all the layers. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) along with the energy dispersive X-ray is employed to image the cross-sectional details and the elements present in each layer of the full cell all-solid-state thin film battery. Impedance spectroscopy was employed to calculate the total conductivity of the fabricated full cell. Obtained results indicates that the full cell NMC/LLTO/LTO thin film batteries can be fabricated employing a sputtering technique for the energy applications. Figure 1

Improving Stability of CO2 Electroreduction by Incorporating Ag NPs in N-Doped Ordered Mesoporous Carbon Structures.

The electroreduction of carbon dioxide (eCO2RR) to CO using Ag nanoparticles as an electrocatalyst is promising as an industrial carbon capture and utilization (CCU) technique to mitigate CO2 emissions. Nevertheless, the long-term stability of these Ag nanoparticles has been insufficient despite initial high Faradaic efficiencies and/or partial current densities. To improve the stability, we evaluated an up-scalable and easily tunable synthesis route to deposit low-weight percentages of Ag nanoparticles (NPs) on and into the framework of a nitrogen-doped ordered mesoporous carbon (NOMC) structure. By exploiting this so-called nanoparticle confinement strategy, the nanoparticle mobility under operation is strongly reduced. As a result, particle detachment and agglomeration, two of the most pronounced electrocatalytic degradation mechanisms, are (partially) blocked and catalyst durability is improved. Several synthesis parameters, such as the anchoring agent, the weight percentage of Ag NPs, and the type of carbonaceous support material, were modified in a controlled manner to evaluate their respective impact on the overall electrochemical performance, with a strong emphasis on operational stability. The resulting powders were evaluated through electrochemical and physicochemical characterization methods, including X-ray diffraction (XRD), N2-physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-EDS, electron tomography, and X-ray photoelectron spectroscopy (XPS). The optimized Ag/soft-NOMC catalysts showed both a promising selectivity (∼80%) and stability compared with commercial Ag NPs while decreasing the loading of the transition metal by more than 50%. The stability of both the 5 and 10 wt % Ag/soft-NOMC catalysts showed considerable improvements by anchoring the Ag NPs on and into a NOMC framework, resulting in a 267% improvement in CO selectivity after 72 h (despite initial losses) compared to commercial Ag NPs. These results demonstrate the promising strategy of anchoring Ag NPs to improve the CO selectivity during prolonged experiments due to the reduced mobility of the Ag NPs and thus enhanced stability.

First-principles calculations to investigate structural stability, electronic properties and mechanical properties of Y element substitutional doped β′-Mg7Gd phase

Based on the experimental characterization results of aberration-corrected (Cs) high-angle-annular dark field-scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectrometry (EDS) diagrams, we systematically investigated the performance of substituting Y for Gd in the β′-Mg7Gd phase. The formation enthalpy, electronic structure, and elastic properties were calculated by first-principles. The calculation results indicated that all structures are thermodynamically stable, and the substitutional doping of one Gd atom replaced by one Y atom is the most stable. The electronic structure plots for the energy of the whole system decreased near the Fermi level, indicating that the system became more stable after substitutional doping. Furthermore, the elastic modulus, particularly Young's modulus and shear modulus, was greatly improved in Mg28Y2Gd2(P2). Elastic anisotropy factors are calculated to evaluate elastic anisotropy, and plot the three-dimensional and projection plots of bulk, shear, and Young's modulus. The extent of elastic anisotropy is ranked as follows: Mg28Y2Gd2(P2) > Mg7Gd(P0) > Mg28YGd3(P1). These results offer valuable data references for the performance evaluation and practical application of rare earth (RE) magnesium alloys.

Adjustment of a novel β′-type precipitate in a creep-aged Mg−15 wt%Gd alloy

A Mg−15 wt%Gd binary alloy was prepared by hot-extrusion and then creep-aged at 200 °C under a constant stress of 200 MPa in this work. Compared with the traditional aging, creep aging clearly accelerated the age-hardening response, as the aging time for the peak yield strength was shorten from 72h to ∼16h. In the peak-creep-aged sample, a novel precipitation structure, named as β′H herein, was observed as the dominant precipitate. Interestingly, these dense β′H precipitates preferred to distributing along a certain direction which generally deviated from the extrusion direction (ED) by 54–67°. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) characterization revealed that this novel β′H precipitate is composed of distorted Gd-rich hexagonal units, with the chemical formula of Mg7Gd2 and having a monoclinic structure, a = 0.671 nm, b = 1.727 nm, c = 0.521 nm and β = 100.7°. Density functional theory (DFT) calculations suggest that the applied stress during creep aging could provide an effective tensile stress for the motion of the surrounding Mg atoms when forming the β′H structure.

Design of Ir/Pt dual electrocatalysts loaded on exfoliated acetylene black for Li air battery application

This study introduces a novel type of electrocatalysts, where Pt and Ir nanoparticles were incorporated onto exfoliated acetylene black (FAB) substrate. These electrocatalysts were engineered to exhibit dual activity, simultaneously facilitating both oxygen reduction reaction and oxygen evolution reaction. The successful creation of these dual-function electrocatalysts, namely FAB180-Pt/Ir and FAB60-Pt/Ir, was confirmed through characterization techniques including transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), energy-dispersive x-ray spectroscopy (EDS), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Ultimately, this bimetallic Pt-Ir catalyst, supported on exfoliated acetylene black (FAB), hold potential for application in Li-air batteries.