Field Scanning Transmission Electron Microscopy Research Articles

Facile synthesis of CoSi alloy catalysts with rich vacancies for base- and solvent-free aerobic oxidation of aromatic alcohols

The rational design and green synthesis of low-cost, robust, and efficient catalysts for the selective oxidation of various alcohols are highly challenging. Herein, we report a fast and solvent-free arc-melting (AM) method to controllably synthesize a semimetallic CoSi alloy catalyst (denoted as AM-CoSi) that is efficient in the base- and solvent-free oxidation of six types of aromatic alcohols. X-ray absorption fine structure analysis, electron paramagnetic resonance spectroscopy, and aberration-corrected high angle annular dark field scanning transmission electron microscopy confirmed the successful synthesis of AM-CoSi with abundant Si vacancies (Siv). The as-prepared CoSi alloy catalysts exhibit an order of magnitude greater activity in the oxidation of a model reactant, benzyl alcohol (BAL) to benzyl benzoate (BBE), compared with their mono-counterparts, and provide 70% yield of BBE, the highest yield reported to date. Experimental results and density functional theory calculations suggest that the CoSi alloy structure improves the BAL conversion and that Si vacancy is the main contributor to the generation of BBE, based on which a potential reaction pathway is rationally proposed. Furthermore, the CoSi alloy maintains high stability and also exhibits high activity in the selective oxidation of various alcohols with different functional groups. This work demonstrates for the first time that semimetallic CoSi alloys can be robust catalysts for the green oxidation of various alcohols and proviedes a vast opportunity for the rational design and application of other semimetal alloy catalysts.

PEI-Schiff base-modified mesoporous silica materials SBA-12, 15 and 16 for toxic metal ions capture (Co(II), Ni(II) and Cu(II)): Effect of morphology, post-synthetic modification and kinetic study

A series of SBA materials (SBA-12, SBA-15, and SBA-16) with polyethyleneimine (PEI) and its Schiff base variants with salicylaldehyde-modified samples (PS) have been successfully prepared and characterized. The synthesized materials were investigated by infrared spectroscopy (FT-IR), and quantification of the organic part coated on the surface was studied using thermogravimetric analysis (TGA). Nitrogen adsorption/desorption analysis at − 196 °C (N2), bright field scanning transmission electron microscopy (BF-STEM) and small angle X-ray scattering (SAXS) measurements were used to study textural properties, structure and morphology. Confirmation of heavy metal ions capture in pores of prepared materials was proved by X-ray fluorescence analysis (XRF), and nitrate anions were confirmed by FT-IR spectroscopy. Kinetic studies were performed by conductometric analysis (CA) and showed that the mathematical models could be applied to adsorption processes with a non-linear decreasing trend. This trend appeared in PS-modified SBA systems and some non-modified samples. The best overall adsorption properties were observed for material SBA-12 and its modified types. In this case, material SBA-12-PS can trap 54.38 mg g−1 of Cu(NO3)2 or 18.42 mg of Cu(II) ions, 112.84 mg g−1 of Ni(NO3)2 corresponding to 36.24 mg of Ni(II) cations, and 39.56 mg g−1 of Co(NO3)2 representing 12.74 mg of Co(II) ions. Non-modified materials show morphological effects where 2D ordered pores with hexagonal symmetry and the biggest mesopores (5.5 nm) have the best overall results in adsorption capacity of metal ions (Cu(II): 11.95 mg g−1) calculated from pseudo-second order. SBA-12 with a cubic framework and 3D ordered pores (3.8 nm) has a lower adsorption capacity than SBA-15 (Cu(II): 7.85 mg g−1), and SBA-16 with the smallest spherical pores (under 2 nm) showed the lowest overall adsorption capacity (Cu(II): 4.65 mg g−1). Kinetic rates of non-modified samples have opposite trend SBA-12 (Cu(II): 0.009 mg g−1 min−1) > SBA-15 (Cu(II): 0.002 mg g−1 min−1) > SBA-16 (Cu(II): 0.001 mg g−1 min−1). In the case of SBA-16, small pore entrances have a negative effect on the kinetic rate. For modified samples, SBA-12 with the largest surface area (896 m2 g−1) provides more space for binding of polyethyleneimine molecules (and also salicylaldehyde), which affects the best results in ion capture (Cu(II): 16.64 mg g−1). Bigger mesopores give more adsorption capacity, but capillarity makes the kinetic rate slow. SBA-16, with tiny entrance mesopores, has the lowest kinetic rate and adsorption capacity. This phenomenon was also observed in cobalt(II) adsorption, and similar results were obtained in nickel(II) adsorption. Kinetic studies point to two types of mechanisms given by the pseudo-second-order model in the case of non-modified materials, and Elovich kinetic model describes chemisorption at modified samples. These mechanisms are influenced by the significant effect of intraparticle diffusion, described by the Weber-Morris model.

Study on microstructure and properties of AA7075 coated by micro arc oxidation

Effect of ageing temperature on the properties of 7075 aluminum alloy coated by micro arc oxidation (MAO) technology has been investigated. The precipitates formed at various ageing temperatures are observed by transmission electron microscope (TEM), which would significantly influence the properties of the MAO coating. Coherent distortion, size and volume fraction of precipitates are related to the changing of electrical conductivity during ageing treatment. Full coherent and dense Guinier Preston zones (GP zones) formed at 90 °C can act as scattering centers to impede electron mobility, so decrease the electrical conductivity. η and η′ phases produced at 120 °C and 150 °C are semi-coherent and incoherent, respectively, meanwhile, the precipitate size increases and the volume fraction decreases with increasing the ageing temperature, therefore, the electrical conductivity increases. Higher electrical conductivity contributes to thicker coating with better surface morphology. Double cantilever beam (DCB) tests show that the thicker and less porous coatings prepared at 150 °C aged specimens own the best stress corrosion cracking (SCC) resistance. After pores are broke and coatings are ruptured, high Cu and low Mg segregation at the grain boundary of 150 °C aged specimens founded from high-angle annular dark field scanning transmission electron microscopy (HADDF-STEM) are beneficial to anodic dissolution and hydrogen assisted crack.

Formation mechanism of trench defects in green InGaN/GaN multiple quantum wells

Trench defects, resulting in low emission efficiency in green and longer spectrum ranges, are widely observed in III-nitride alloy multiple quantum wells (MQWs), particularly in those with high indium content. There is a lack of understanding of the atomic formation mechanism of trench defects; however, it is crucial to the efficiency of devices. Here, we provided a thermodynamic analysis through first-principles calculations based on the density functional theory combined with experimental confirmation to reveal the atomic formation mechanism of trench defects in the InGaN MQWs system. The In-rich region is easy to form and induces basal plane stacking faults (BSFs) at the interface between the InGaN quantum well and the GaN quantum barrier (QB). The boundary between BSF and non-BSF regions exhibits a much slower growth rate due to the formation of homoelementary bonds, resulting in a V-shaped groove shape. Based on high-angle annular dark field scanning transmission electron microscopy, we observe the trench defects originating from the thick GaN QB layer due to the formation of closed-loop V-shaped grooves and the BSF. Besides, the cathodoluminescence measurements show that the InGaN QW within the defect has excess indium and poor crystal quality.

A Low-Temperature Synthetic Route Toward a High-Entropy 2D Hexernary Transition Metal Dichalcogenide for Hydrogen Evolution Electrocatalysis.

High-entropy (HE) metal chalcogenides are a class of materials that have great potential in applications such as thermoelectrics and electrocatalysis. Layered 2D transition-metal dichalcogenides (TMDCs) are a sub-class of high entropy metal chalcogenides that have received little attention to date as their preparation currently involves complicated, energy-intensive, or hazardous synthetic steps. To address this, a low-temperature (500 °C) and rapid (1h) single source precursor approach is successfully adopted to synthesize the hexernary high-entropy metal disulfide (MoWReMnCr)S2 . (MoWReMnCr)S2 powders are characterized by powder X-ray diffraction (pXRD) and Raman spectroscopy, which confirmed that the material is comprised predominantly of a hexagonal phase. The surfaceoxidation states and elemental compositions are studied by X-ray photoelectron spectroscopy (XPS) whilst the bulk morphology and elemental stoichiometry with spatial distribution is determined by scanning electron microscopy (SEM) with elemental mapping information acquired fromenergy-dispersive X-ray (EDX) spectroscopy. The bulk, layered material is subsequently exfoliated to ultra-thin, several-layer 2D nanosheets by liquid-phase exfoliation (LPE). The resultingfew-layer HE (MoWReMnCr)S2 nanosheets are found to contain a homogeneous elemental distribution of metals at the nanoscale by high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) with EDX mapping. Finally, (MoWReMnCr)S2 is demonstrated as a hydrogen evolution electrocatalyst and compared to 2H-MoS2 synthesized using the molecular precursor approach. (MoWReMnCr)S2 with 20% w/w of high-conductivity carbon black displays a low overpotential of 229mV in 0.5 M H2 SO4 to reach a current density of 10mA cm-2 , which is much lower than the overpotential of 362mV for MoS2 . From density functional theory calculations, it is hypothesised that the enhanced catalytic activity is due to activation of the basal plane upon incorporation of other elements into the 2H-MoS2 structure, in particular, the first row TMs Cr and Mn.

Boosting the Catalytic Performance of AuAg Alloyed Nanoparticles Grafted on MoS2 Nanoflowers through NIR-Induced Light-to-Thermal Energy Conversion.

MoS2 nanoflowers (NFs) obtained through a hydrothermal approach were used as the substrate for the deposition of tiny spherical bimetallic AuAg or monometallic Au nanoparticles (NPs), leading to novel photothermal-assisted catalysts with different hybrid nanostructures and showing improved catalytic performance under NIR laser irradiation. The catalytic reduction of pollutant 4-nitrophenol (4-NF) to the valuable product 4-aminophenol (4-AF) was evaluated. The hydrothermal synthesis of MoS2 NFs provides a material with a broad absorption in the Vis-NIR region of the electromagnetic spectrum. The in situ grafting of alloyed AuAg and Au NPs of very small size (2.0-2.5 nm) was possible through the decomposition of organometallic complexes [Au2Ag2(C6F5)4(OEt2)2]n and [Au(C6F5)(tht)] (tht = tetrahydrothiophene) using triisopropilsilane as reducing agent, leading to nanohybrids 1-4. The new nanohybrid materials display photothermal properties arising from NIR light absorption of the MoS2 NFs component. The AuAg-MoS2 nanohybrid 2 showed excellent photothermal-assisted catalytic activity for the reduction of 4-NF, which is better than that of the monometallic Au-MoS2 nanohybrid 4. The obtained nanohybrids were characterised by transmission electron microscopy (TEM), High Angle Annular Dark Field-Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy (HAADF-STEM-EDS), X-ray photoelectron spectroscopy and UV-Vis-NIR spectroscopy.

Shear strain rate sensitivity and crystallisation kinetics investigation in melt spun Cu64Zr36 binary metallic glass

Abstract Shear strain rate effect on crystallisation behaviour and characteristic temperatures of the three well-known glass formers in Cu–Zr binary amorphous system, namely Cu50Zr50, Cu56Zr44 and Cu64Zr36, were investigated. The crystallisation behaviour of Cu64Zr36 was uniquely found to be heavily dependent on shear strain rate. Crystallisation kinetics were studied through Isochronal transformation and isothermal transformation. The activation energy of crystallisation of each case was compared and contrasted. Johnson-Mehl-Avrami (JMA) analyses were also employed to study its kinetics behaviour. Finally, high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) combined with laser-assisted local electrode atom probe (LEAP) investigation revealed no detectable clustering or phase separation.

Complexions at carbide / binder grain boundaries of Re-containing submicron cemented carbide

Samples of submicron WC-Co-Re cemented carbide were produced and examined by different techniques. The microstructure of the samples is fine and extremely uniform indicating the strong inhibiting effect of Re with respect to the WC grain growth during liquid-phase sintering. Results of examination of hot hardness at a temperature of 500°C provide evidence for the significantly higher hardness value of the WC-Co-Re cemented carbide in comparison with that of a conventional submicron WC-Co grade. Studies of creep rates of WC-Co-Re and WC-Co cemented carbides at 800°C indicated dramatically improved high-temperature creep-resistance of the Re-containing cemented carbide. Carbide / binder grain boundaries in a FIB lamella prepared from the WC-Co-Re cemented carbide were examined by high-angle annular dark field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy at a high resolution. Rhenium was found to segregate at the grain boundaries forming complexions of 2 to 3 atomic monolayers, which presumably consist of mixed W-Re carbide. Such complexions are believed to suppress the phenomena of grain boundary sliding at elevated temperatures and WC grain growth at sintering temperatures thus dramatically improving the high-temperature creep-resistance of the WC-Co-Re material in comparison with conventional WC-Co cemented carbide.

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta-Coordinated Sites.

Atomic Fe in N-doped carbon (FeNC) electrocatalysts for oxygen (O2 ) reduction at the cathode of proton exchange membrane fuel cells are the most promising alternative to platinum-group-metal catalysts. Despite recent progress on atomic FeNC O2 reduction, their controlled synthesis and stability for practical applications remain challenging. A two-step synthesis approach has recently led to significant advances in terms of Fe-loading and mass activity; however, the Fe utilization remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, this issue is addressed by coordinating Fe in a highly porous nitrogen-doped carbon support (≈3295m2 g-1 ), prepared by pyrolysis of inexpensive 2,4,6-triaminopyrimidine and a Mg2+ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54×1019 sitesgFeNC -1 and a record 52% FeNx electrochemical utilization based on in situ nitrite stripping are achieved. The Fe single atoms are characterized pre- and post-electrochemical accelerated stress testing by aberration-corrected high-angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X-ray absorption spectroscopy and low-temperature Mössbauer spectroscopy suggest the presence of penta-coordinated Fe sites, which are further studied by density functional theory calculations.

Ag Aerogel-Supported Single-Atom Hg Nanozyme Enables Efficient SERS Monitoring of Enhanced Oxidase-Like Catalysis.

In this work, three-dimensional (3D) Ag aerogel-supported Hg single-atom catalysts (SACs) were explored as an efficient surface-enhanced Raman scattering (SERS) substrate to monitor the enhanced oxidase-like reaction. The influence of the concentrations of Hg2+ to prepare 3D Hg/Ag aerogel networks on their SERS properties to monitor the oxidase-like reaction has been investigated, and a specific enhancement with an optimized addition of Hg2+ has been achieved. The formation of Ag-supported Hg SACs with the optimized Hg2+ addition was identified from a high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image and X-ray photoelectron spectroscopy (XPS) measurement at an atomic level. This is the first discovery of Hg SACs for enzyme-like reaction applications inferred by SERS techniques. And density functional theory (DFT) was used to further reveal the oxidase-like catalytic mechanism of Hg/Ag SACs. This study provides a mild synthetic strategy to fabricate Ag aerogel-supported Hg single atoms to display promising prospects in various catalytic fields.

Partially Thiolated Au25 Cluster Anchored on Carbon Support via Noncovalent Ligand–Support Interactions: Active and Robust Catalyst for Aerobic Oxidation of Alcohols

Partially thiolated atomically precise Au cluster catalysts were developed by controlled calcination of presynthesized thiolate-protected Au clusters on a porous carbon support. X-ray absorption fine structure analysis, powder X-ray diffraction, and aberration-corrected high-angle annular dark field scanning transmission electron microscopy revealed that calcination of 1 wt % of Au25(SR)18 (RS = 2-phenylethanethiolate, 1-dodecanethiolate) on carbon at 450 °C for 8–12 h produced partially thiolated Au25 clusters Au25(SR)/C without sintering. The Au25(SR)/C catalyst exhibited comparable catalytic activity to that of the thiolate-free Au25 cluster Au25/C for benzyl alcohol oxidation, whereas Au25(SR)/C showed higher durability than Au25/C. These results suggested that the residual RS ligands were distributed at the interface between the clusters and the support and suppressed the diffusion of the clusters by multiple van der Waals interactions. Large kinetic isotope effects indicated that the hydride abstraction from the α-carbon of the alkoxide was the rate-determining step. The O2 pressure dependence on rate constants was comparable to that reported for negatively charged Au clusters stabilized by poly(N-vinyl-2-pyrrolidone). This comparison suggests that electron-rich Au atoms left behind by desorbed RS served as active sites, which was supported by density functional theory calculations on model clusters. The partially thiolated Au25 cluster catalysts oxidized various p-substituted benzyl alcohols and benzylic secondary alcohols, with turn-over numbers exceeding 1 × 104. This work demonstrates that partially ligated, atomically precise metal clusters anchored by noncovalent ligand–support interaction are promising model catalysts with both high activity and durability.

Phase transformation and radiation resistance of B-site high entropy pyrochlores

Two high entropy pyrochlores (HEPs), Gd2(Ti0.2Zr0.2Sn0.2Hf0.2Ta0.2)2O7 and Gd2(Ti0.2Zr0.2Sn0.2Hf0.2Nb0.2)2O7 have been synthesized and irradiated with 800 keV Kr2+ ions and examined by in situ transmission electron microscopy (TEM). The irradiation-induced order-to-disorder phase transformation from pyrochlore to the fluorite structure in these two HEPs and Gd2Sn2O7 was observed by using selected area electron diffraction (SAED), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and energy dispersive spectroscopy (EDS) mapping. The cation antisite defect (CAD) formation energy and the electron localization function (ELF) were calculated using density functional theory (DFT). Both the experimental results and calculated results suggest that the HEPs exhibit a higher resistance to phase transformation and amorphization than Gd2Sn2O7.

Biogenic synthesis of noble metal nanoparticles using Melissa officinalis L. and Salvia officinalis L. extracts and evaluation of their biosafety potential

In this study we targeted the noble metal nanoparticles (MNPs) biogenic synthesis capacity of two medicinal species with therapeutic potential, namely Melissa officinalis L. (lemon balm) and Salvia officinalis L. (sage), cultivated in Romania. Plant material was extracted by maceration, microwave assisted extraction (MAE) and ultrasound assisted extraction (UAE). Bright field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (BFSTEM-EDS) techniques were used in order to investigate particles shape, dispersion and chemical elemental analysis. The total polyphenol content for both simple extracts and nanostructured mixtures was determined using the Folin-Ciocalteu method and antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Identification and quantification of secondary metabolites of M. officinalis and S. officinalis were performed by ultra-high performance liquid chromatography (UHPLC). The Allium assay was used to evaluate the potential cytogenotoxic activity, for both simple and nanostructured phytochemical complexes, in the case of S. officinalis L. species being performed for the first time. Spherical shaped MNPs with diameters of about 20 nm were biosynthesised in lemon balm extracts. Larger AuNPs were phytosynthesized in sage extract obtained by UAE. Compared to the simple extracts, the antioxidant capacity as well as the amount of total polyphenols in the nanostructured extracts decreased, substantiating the involvement of bioorganic material in the reduction of metal ions. Low frequency of chromosomal aberrations corresponding to crude extracts and extracts supplemented with MNPs, suggest the cytoprotective, antigenotoxic, and safe use of these plant species as potential therapeutic forms in various diseases.

Hardening effect and precipitation evolution of an isothermal aged Mg-Sm based alloy

The age-hardening behavior and precipitation evolution of an isothermal aged Mg−5Sm−0.6Zn−0.5Zr (wt.%) alloy have been systematically investigated by means of transmission electron microscopy (TEM) and atomic-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The Vickers hardness of the present alloy increases first and then decreases with ageing time. The sample aged at 200 °C for 10 h exhibits a peak-hardness of 90.5 HV. In addition to the dominant β0′ precipitate (orthorhombic, a = 0.642 nm, b = 3.336 nm and c = 0.521 nm) formed on {11-20}α planes, a certain number of γ” precipitate (hexagonal, a = 0.556 nm and c = 0.431 nm) formed on basal planes are also observed in the peak-aged alloy. Significantly, the basal γ” precipitate is more thermostable than prismatic β0′ precipitate in the present alloy. β0′ precipitates gradually coarsened and were even likely to transform into β1 phase (face centered cubic, a = 0.73 nm) with the increase of ageing time, which accordingly led to a gradual decrease in number density of precipitates and finally resulted in the decreased hardness and mechanical property in the over-aged alloys.

Structure of V-defects in long wavelength GaN-based light emitting diodes

The V-defect is a naturally occurring inverted hexagonal pyramid structure that has been studied in GaN and InGaN growth since the 1990s. Strategic use of V-defects in pre-quantum well superlattices or equivalent preparation layers has enabled record breaking efficiencies for green, yellow, and red InGaN light emitting diodes (LEDs) utilizing lateral injection of holes through the semi-polar sidewalls of the V-defects. In this article, we use advanced characterization techniques such as scattering contrast transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, x-ray fluorescence maps, and atom probe tomography to study the active region compositions, V-defect formation, and V-defect structure in green and red LEDs grown on (0001) patterned sapphire and (111) Si substrates. We identify two distinct types of V-defects. The “large” V-defects are those that form in the pre-well superlattice and promote hole injection, usually nucleating on mixed (Burgers vector b=±a±c) character threading dislocations. In addition, “small” V-defects often form in the multi-quantum well region and are believed to be deleterious to high-efficiency LEDs by providing non-radiative pathways. The small V-defects are often associated with basal plane stacking faults or stacking fault boxes. Furthermore, we show through scattering contrast transmission electron microscopy that during V-defect filling, the threading dislocation, which runs up the center of the V-defect, will “bend” onto one of the six {101¯1} semi-polar planes. This result is essential to understanding non-radiative recombination in V-defect engineered LEDs.

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

AbstractThe copper‐catalyzed electrochemical CO2 reduction reaction represents an elegant pathway to reduce CO2 emissions while producing a wide range of valuable hydrocarbons. The selectivity for these products depends strongly on the structure and morphology of the copper catalyst. However, continued deactivation during catalysis alters the obtained product spectrum. In this work, we report on the stabilizing effect of three different carbon supports with unique pore structures. The influence of pore structure on stability and selectivity was examined by high‐angle annular dark field scanning transmission electron microscopy and gas chromatography measurements in a micro‐flow cell. Supporting particles into confined space was found to increase the barrier for particle agglomeration during 20 h of chronopotentiometry measurements at 100 mA cm−2 resembling long‐term CO2 reduction conditions. We propose a catalyst design preventing coalescence and agglomeration in harsh electrochemical reaction conditions, exemplarily demonstrated for the electrocatalytic CO2 reduction. With this work, we provide important insights into the design of stable CO2 electrocatalysts that can potentially be applied to a wide range of applications.

Atomic scale analysis of Zn2+ storage in robust tunnel frameworks.

Realizing rapid and reversible Zn2+ storage at the cathode is imperative for the advancement of aqueous Zn-ion batteries (ZIBs), which offer an excellent option for large-scale electrochemical energy storage. However, owing to limitations of the structural stability of previously investigated frameworks, the Zn2+ storage processes remain unclear, thus hindering progress towards the above goal. Herein, we present the novel application of MoVTe oxide with an M1 phase (MVT-M1) as a potential cathode material for ZIBs. MVT-M1 features broad and robust tunnels that facilitate reversible Zn2+ insertion/extraction during cycling, as well as rich redox centers (Mo, V, and Te) to aid in charge redistribution, resulting in good performances in ZIBs. The exceptional resilience of MVT-M1 to high-energy electron beams allows for direct observation of Zn2+ insertion/extraction at the atomic scale within the tunnels for the first time using high-angle annular dark field scanning transmission electron microscopy; the storage location of zinc ions within the cathode is accurately determined layer by layer from the surface to the bulk phase by employing time-of-flight secondary ion mass spectrometry. Additionally, solvent molecules (H2O and methanol) are also found inside the tunnels along with Zn2+. Due to the broader heptagonal tunnels and Te ions in the hexagonal tunnels, MVT-M1 exhibits good cycling stability, outperforming MoVTe oxide with the M2 phase (no heptagonal tunnels) and MoV oxide with the M1 phase (no Te). These findings hold significant importance in advancing our understanding of the Zn2+ storage mechanism and enable the design of novel materials specifically optimized for efficient Zn2+ storage.

Single-atom thermoelectric materials: a new opportunity

Single-atom materials show great potential in the field of thermoelectrics due to their distinguishing features such as maximum atom utilization efficiency, unique electronic structure, guest−host interactions, and a tunable coordination environment. Herein, the concept of single-atom thermoelectric materials is presented. Thereafter, we introduce characterization techniques including high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure spectroscopy (XAFS) for identifying the specific coordination environment of single atoms. Furthermore, a typical work demonstrating the effect of single atoms on the thermoelectric transport properties of Bi2S3 is provided. Finally, we propose possible future development paths for single-atom thermoelectric materials. This paper provides a reference for further studies of single-atom thermoelectric materials.

Lead-chlorine synergistic immobilization mechanism in municipal solid waste incineration fly ash (MSWIFA)-based magnesium potassium phosphate cement.

The high chlorine (Cl) and lead (Pb) content characteristics of municipal solid waste incineration fly ash (MSWIFA) pose environmental risks and hinder resource utilization. Herein, an MSWIFA-based magnesium potassium phosphate cement (MKPC) preparation strategy was developed, which allowed the MSWIFA recycling and the Pb-Cl synergistic immobilization without the washing pretreatment. The compressive strength of the resulting 10wt% MSWIFA-based MKPC was 28.44MPa, with over 99.2% reduction in leaching toxicity of Pb and Cl. The high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) and X-ray absorption spectroscopy (XAS) analyzes showed that Pb, phosphate and Cl- formed Pb5(PO4)3Cl in MKPC. In-situ X-ray diffraction (XRD) tests showed that Pb3(PO4)2 was gradually transformed to Pb5(PO4)3Cl through a dissolution-precipitation process. The formation energy, Bader charge, charge density difference and density of states (DOS) of Pb5(PO4)3Cl were analyzed by first-principles calculations, confirming that Pb5(PO4)3Cl was more thermodynamically stable than Pb3(PO4)2 and PbCl2 and that electronic interactions between Pb-p, O-p, P-p and Cl-p orbits were the origin of Pb-Cl synergistic immobilization. This work provides a new strategy for the resource utilization of MSWIFA without washing pretreatment, and provides an in-depth understanding of the Pb-Cl synergistic immobilization mechanism.

High-performance atomic Co/N co–doped porous carbon catalysts derived from Co–doped metal–organic frameworks for oxygen reduction

Improving the activity and durability of carbon-based catalysts is a key challenge for their application in fuel cells. Herein, we report a highly active and durable Co/N co-doped carbon (CoNC) catalyst prepared via pyrolysis of Co–doped zeolitic–imidazolate framework–8 (ZIF–8), which was synthesized by controlling the feeding sequence to enable Co to replace Zn in the metal–organic framework (MOF). The catalyst exhibited excellent oxygen reduction reaction (ORR) performance, while the half-wave potential decreased by only 8 mV after 5,000 accelerated stress test (AST) cycles in an acidic solution. Furthermore, the catalyst exhibited satisfactory cathodic catalytic performance when utilized in a hydrogen/oxygen single proton exchange membrane (PEM) fuel cell and a Zn-air battery, yielding maximum power densities of 530 and 164 mW cm−2, respectively. X-ray absorption spectroscopy (XAS) and high-angle annular dark field-scanning transmission electron microscopy (HAAD–STEM) analyses revealed that Co was present in the catalyst as single atoms coordinated with N to form Co–N moieties, which results in the high catalytic performance. These results show that the reported catalyst is a promising material for inclusion into future fuel cell designs.