Large Vacancy Research Articles

Large scale and oxygen vacancy VO2 porous thin sheets to enable high-performance zinc ion storage.

Herein, we report the first result of large scale and oxygen vacancy VO2 porous thin sheets assembled by a 3D interconnected nanoflake array framework, which is recorded as VOd. The as-prepared VOd was characterized by various methods and Zn2+ intercalation/deintercalation and structural decomposition mechanisms were proposed based on ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

A comparative study on the linear scaling relations for the diffusion of S-vacancies on MoS2 and WS2.

This work uses density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations to compare the diffusion of S-vacancies on defective MoS2 and WS2, two structures that are often discussed as catalysts. Similar to what has been discussed for MoS2, the vacancy diffusion barriers on WS2 also follow Brønsted-Evans-Polanyi (BEP) type linear scaling relations. The vacancy diffusion kinetics is discussed at the example of a large vacancy cluster consisting of 37 unoccupied sites in direct vicinity and how its structure changes with time. Using barriers estimated via linear scaling relations as input for the kMC simulations yields results that qualitatively agree with results calculated self-consistently at DFT level. As the diffusion barriers for WS2 are significantly higher than those for MoS2, the vacancy diffusion on WS2 is poorly described by the linear scaling relations derived from MoS2 and vice versa. This work further shows that one needs DFT level barriers of about 40% of all S-vacancy diffusion processes on a material to derive sufficiently reliable linear scaling relations. This means that computational costs for future studies may be reduced by only explicitly computing one fraction of the diffusion barriers while estimating the remaining ones via linear scaling. However, in this case, one would lack information about the partition function of the transition states, which are needed for calculating the rate constants. Thus, we have also proposed a scheme to estimate the contribution of the partition functions based only on the initial state's vibrational modes.

Highly Active and Water-Resistant Cu-Doped OMS-2 Catalysts for CO Oxidation: The Importance of the OMS-2 Synthesis Method and Cu Doping.

Porous cryptomelane-type Mn oxide (OMS-2) has an outstanding redox property, making it a highly desirable substitute for noble metal catalysts for CO oxidation, but its catalytic activity still needs to be improved, especially in the presence of water. Given the strong structure-performance correlation of OMS-2 for oxidation reactions, herein, OMS-2 is synthesized by solid state (OMS-2S), reflux (OMS-2R), and hydrothermal (OMS-2H) methods, aiming to improve its CO oxidation performance through manipulating synthesis parameters to tailor its particle size, morphology, and crystallinity. Characterization shows that OMS-2S has the highest CO oxidation activity in the absence of water due to its low crystallinity, high specific surface area, large oxygen vacancy content, and good redox property, but the presence of water can greatly reduce its CO oxidation activity. Doping Cu into an OMS-2 can not only improve its CO oxidation activity but also greatly improve its water tolerance. The Cu-doped OMS-2S catalyst with ∼4 wt % Cu can achieve a T90 of 49 °C (1% CO/10% O2/N2 and WHSV = 60,000 mL·g-1·h-1), ranking among the lowest reported T90 values for Mn oxide-based CO oxidation catalysts, and it can maintain nearly 100% CO conversion in the presence of 5 vol % water for over 50 h. In situ DRIFTs characterization indicates that the good water resistance of Cu-doped OMS-2S can be attributed to the significantly suppressed surface hydroxyl group generation because of Cu doping. This work demonstrates the importance of the synthesis method and Cu doping in determining the CO oxidation activity and water resistance of OMS-2 and will provide guidance for synthesizing highly active and water-resistant CO oxidation catalysts.

ZnO nanowire/NiO foam 3D nanostructures for high-performance ethylene glycol sensing

Ethylene glycol is widely used in industrial production but poses potential safety hazards to human life and health. Unfortunately, conventional glycol gas sensors have limitations that impede their effectiveness, such as sluggish response rates, high operational temperatures, and complex preparation procedures. A new approach has been explored to address these challenges. A ZnO nanowire/NiO foam nanostructured sensor was developed specifically for rapid ethylene glycol detection. The NiO/ZnO heterojunction-based gas sensor (NZO-6) has inherent p-type gas-sensitive characteristics. Notably, it delivers a response of 58.98–100 ppm of ethylene glycol at a relatively low operating temperature of 175 ℃. At a relatively low operating temperature of 175 ℃, it exhibits a response of 58.98–100 ppm ethylene glycol, 2.28 times higher than NiO foam, and a fast response/recovery time (4 s/26 s). This improvement is attributed to the porous structure of NiO foam/ZnO nanowires, with a large specific surface area and numerous oxygen vacancies generated during synthesis. Additionally, the catalysis of Ni metal and the formation of p/n heterojunctions further contribute to the improved sensing performance. This research offers a promising solution for developing high-performance ethylene glycol gas sensors with potential environmental monitoring, industrial safety, and public health applications. Further, this synthesis method provides an effective strategy for constructing other NiO-based heterostructure-based gas sensors.

AC Conduction Mechanism and Impedance Analysis of Conventional and Plasma‐Sintered Yttria‐Stabilized ZrO2@Mullite Composite

AbstractThe addition of 8 mol% of Y2O3 to the ZrO2@mullite composites stabilizes the metastable tetragonal phase of ZrO2 in conventional and plasma‐sintered Y2O3‐stabilized ZrO2@mullite composites. A fused, highly dense, and interconnected microstructure is formed in the case of plasma‐sintered Y2O3 stabilized ZrO2@mullite composite. At 1 MHz frequency, the room temperature and tanδ of (10.37 and 2.06) is obtained for the conventional Y2O3 stabilized ZrO2@mullite composite and that of (38.8 and 4.02) is observed for the plasma sintered Y2O3 stabilized ZrO2@mullite composite. The substitution of Y3+ in place of Zr4+ creates sufficiently large oxygen vacancies at the grain boundary regions of these composites endowed mostly with the ZrO2 phase. In conventional Y2O3‐ ZrO2@mullite composites, both dielectric relaxation as well as conductivity relaxation are observed due to the dynamic motion of dipoles and relaxation due to the presence of defect states and porous structures. This leads to higher grain boundary conductivity than the grain conductivity of these composites. Thermally activated conduction mechanisms exhibited in these composite materials are projected from the complex impedance and modulus analysis. The conventional and plasma sintered Y2O3‐ ZrO2@mullite composite has an optical bandgap of 3.26 and 3.58 eV, respectively.

Impact of nanosecond laser annealing on vacancies in electroplated Cu films studied by monoenergetic positron beams

Positron annihilation was used to probe vacancy-type defects in electrodeposited Cu films after nanosecond pulse laser annealing. For the as-deposited Cu film, we identified the coexistence of two different vacancy-type defects, vacancy clusters (such as V16) and monovacancy-type defects, coupled with impurities. An enlargement in the vacancy size was observed after the laser annealing process. The size of these defects was estimated to be close to V30, and such defects could not be formed by conventional furnace annealing. After furnace annealing at 400 °C, the size of the larger vacancy clusters decreased, but that of the smaller vacancies increased. The observed change in the sizes of vacancies is considered to be related to interactions between vacancies and impurities. The depth profile of the defects varied by changing the laser energy density and the number of laser shots. The impact of laser annealing on the vacancy-type defects was observed even after furnace annealing at 800 °C. Because the presence of point defects in electroplated Cu directly correlates with electromigration and grain growth, the ability of laser annealing to introduce large vacancy clusters in the localized region shows the potential of nanosecond laser annealing as a low-thermal budget process tool for back-end-of-line materials.

Modulating the p-band center of carbon nanofibers derived from Co spin state as anode for high-power sodium storage

Carbon nanofibers (CNFs) have received extensive and in-depth studied as anodes for sodium-ion batteries (SIBs), and yet their initial Coulombic efficiency and rate capability remain enormous challenge at practical level. Herein, CNFs anchored with cobalt nanocluster (CNFs-Co) were prepared using chemical vapor deposition and thermal reduction methods. The as-prepared CNFs-Co shows a high initial Coulombic efficiency of 91% and a high specific discharge capacity of 246 mAh/g at 0.1 A/g after 200 cycles as anode for SIBs. Meanwhile, the CNFs-Co anode still delivers a high cycling stability with 108 mAh/g after 1000 cycles at 10 A/g. These excellent electrochemical properties could be attributed to the involved spin state Co, which endows CNFs with large interplanar spacing (0.39 nm) and abundant vacancy defects. Importantly, the spin state Co downshifts the p-band center of carbon and strengthens the Na+ adsorption energy from −2.33 eV to −2.64 eV based on density functional theory calculation. This novel strategy of modulating the carbon electronic structure by the spin state of magnetic metals provides a reference for the development of high-performance carbon-based anode materials.

Modulating the large vacancy types of CuS ultrathin nanosheets via defect engineering to improve the photocatalytic antibacterial performance

Defect engineering is emerging as an important tool for tuning the photocatalytic antibacterial properties of nanomaterials. However, its development is constrained by the lack of exploration of defect engineering for large defect types. We designed CuS and CuS-200 ultrathin nanosheets with different large vacancy types VCuSSCuCu and VCuSSCuCuCu, respectively. The antibacterial test results demonstrated that CuS-200 ultrathin nanosheets exhibited stronger bactericidal effect on Escherichia coli (E. coli) than CuS under near-infrared (NIR) light. The high antibacterial efficiency was attributed to the improved energy band structure, which helped CuS-200 absorb light and improved photothermal conversion efficiency. In addition, the optimized electronic structure and the strong oxygen adsorption ability drove CuS-200 to produce a large amount of reactive oxygen species (ROS). This work provided new ideas for the preparation of efficient bactericides and new strategies for the design and preparation of catalysts with specific photocatalytic properties.

Determination of uric acid in serum by SERS system based on VO-MnCo2O4/Ag nanozyme

The level of uric acid is crucial to human health. Octahedral oxygen vacancy MnCo2O4/Ag (VO-MnCo2O4/Ag) nanozyme was successfully prepared by simple hydrothermal, calcination and self-reduction methods. VO-MnCo2O4/Ag nanozyme is rich in Mn2+/Mn3+ and CO2+/CO3+ redox electron pairs, large specific surface area and oxygen vacancies. VO-MnCo2O4/Ag nanozyme showed high uricase-like activity and peroxidase-like activity. At the same time, the SERS signal of the detected molecule could be significantly enhanced after the catalytic reaction of the VO-MnCo2O4/Ag nanozyme. The Km values of VO-MnCo2O4/Ag nanozyme for H2O2 and TMB were 0.04 mM and 0.027 mM respectively. Based on the uric acid oxidase-like and peroxidase-like activities of VO-MnCo2O4/Ag, we developed a label-free, sensitive, and reliable SERS uric acid detection system. The detection linear range of uric acid is 0.01 μM–1000 μM and the detection of limit is 7.8 × 10−9 M. The results show that the sensing system has good accuracy, sensitivity, selectivity, and stability. It can be applied to the determination of samples under different conditions. This study provides profound insights into the design of enzyme-like activity regulation and SERS properties regulation of nanozymes, provides guidance for the study of reaction kinetics and catalytic mechanism of nanozymes, and has broad application prospects in the field of nanozymes and SERS sensing analysis.

Hydrogen Bonding Induced Confinement Effect between Ultrafine Nanowires and Polymer Chains for Low-Energy-Barrier Ion Transport in Composite Electrolytes.

Achieving low-energy-barrier lithium ion transport is a fundamental issue for composite solid-state electrolytes (CSEs) in all-solid-state lithium metal batteries (ASSLMBs). In this work, a hydrogen bonding induced confinement strategy was proposed to construct confined template channels for low-energy-barrier lithium ion continuous transport. Specifically, the ultrafine boehmite nanowires (BNWs) with 3.7 nm diameter were synthesized and superiorly dispersed in a polymer matrix to form a flexible CSE. The ultrafine BNWs with large specific surface areas and abundant oxygen vacancies assist the dissociation of lithium salts and confine the conformation of polymer chain segments by hydrogen bonding between the BNWs and the polymer matrix, thus forming a polymer/ultrafine nanowire intertwined structure as template channels for dissociated lithium ions continuous transport. As a result, the as-prepared electrolytes displayed a satisfactory ionic conductivity of 0.714 mS cm-1 and low energy barrier (16.30 kJ mol-1), and the assembled ASSLMB delivered excellent specific capacity retention (92.8%) after 500 cycles. This work demonstrates a promising way to design CSEs with high ionic conductivity for high-performance ASSLMBs.

Enhancements on oxygen vacancy and light absorption of alkaline-etched BiVO4 for photoelectrochemical water oxidation

Designing the favorable morphology with large surface area and abundant oxygen vacancies for BiVO4 can enhance its electron diffusion lengths and improve its photocatalytic ability toward photoelectrochemical water oxidation. The ex-situ alkaline etching process is reported to be facile for enhancing the light absorption and oxygen vacancy of BiVO4, but the systematic study of alkaline etching on the photocatalytic ability of BiVO4 is rare. In this study, alkaline-etched BiVO4 is firstly fabricated using a hydrothermal process with different durations as the photocatalyst of water oxidation. The BiVO4 etched by alkaline for longer durations presents rougher surface, more oxygen vacancies and higher light absorption. The larger carrier densities and the smaller charge-transfer resistances are also achieved for the alkaline etched BiVO4. The largest photocurrent density of 2.38 mA/cm2 is achieved at 1.23 V versus reversible hydrogen electrode in the Na2SO4 electrolyte for BiVO4 etched by alkaline for 45 min, while the pristine BiVO4 electrode only shows a photocurrent density of 0.59 mA/cm2. The photocurrent retention of 81% is also obtained for the alkaline etched BiVO4 electrode after continuous illumination for 6000 s. The results imply the feasibility of applying the alkaline etching process on refining the photoelectrochemical catalytic ability of BiVO4.

Boosting Oxygen Reduction Activity of Co3O4 through a Synergy of Ni Doping and Carbon Species Dotting for Zn-air Battery

Oxygen reduction reaction (ORR) undertakes an indispensable driving role for metal-air batteries with sluggish kinetics. In this work, we proposed a synergic strategy of Ni doping and carbon species dotting to compose Co3O4 with intrinsic large specific area and oxygen vacancies. The Ni-doped Co3O4/C (NCC-1) with four electron transfer mode conducts extraordinary electrocatalytic performance than commercial 20 wt% Pt/C and excellent tolerance to methanol poisoning. This series of improvements are attributed to the rapid dynamics drove by variable transition metal valence with elevated electronic conductivity derived from dotted carbon species. The XPS results at different reduction stages investigate that the doped Co3O4/C affects ORR performance by adjusting the species of *O at the active sites and the formation of intermediates including *OH and *O. More Co3+ active sites exposed on the NCC-1 surface, higher catalytic activity is provided by the conversion of Co(Ⅱ)/Co(III) and Ni(Ⅱ)/Ni(III). What is purposeful in practicability. the NCC-1/IrO2 based Zn-air batteries show an excellent charge-discharge response and cyclability than that of 20% Pt/IrO2 based Zn-air batteries, highlighting the implemented potentiality of NCC-1 based metal-air-battery. This study offers new insights into designing non-noble-metal based oxygen reduction electrocatalysts for more energy storage devices.

An aliovalent‐substituted inorganic-open-framework anode for high-performance potassium-ion batteries

Potassium-ion batteries have drawn great attention owing to the abundant and low-cost potassium resources. However, the lack of highly reversible K+-storage electrodes remains a key concern, due to the large size of K+ ions. Inorganic-open-framework KTiOPO4-type (KTP) anodes are promising K+-hosts, due to their large interstitial vacancies allowing fast and reversible insertion of K+ ions with low structural evolution. Here, we report a new member in the KTP family, K0.63Cr0.56Ti0.55OPO4 (KCTP), with partial aliovalent substitution. The KCTP exhibits a high specific capacity of 123.4 mAh/g and achieves stable cycle life, over 135 days with 98% capacity retention at 10 mA/g and up to 9.9 months with 81% retention at 20 mA/g. The K+-storage process involves biphasic reaction and solid-solution reaction, with a minor volume change of only 8.06%. This work demonstrates that inorganic open frameworks with aliovalent substitution may open a promising way to design high-performance potassium-ion batteries.

Defect properties of a body-centered cubic equiatomic TiVZrTa high-entropy alloy from atomistic simulations

TiVZrTa high-entropy alloys (HEAs) have been experimentally proven to exhibit excellent irradiation tolerance. In this work, defect energies and evolution were studied to reveal the underlying mechanisms of the excellent irradiation tolerance in TiVZrTa HEA via molecular statics calculations and molecular dynamics simulations. The atomic size mismatch of TiVZrTa is ∼6%, suggesting a larger lattice distortion compared to most face-centered cubic and body-centered cubic M/HEAs. Compared to pure Ta and V, smaller vacancy formation and migration energies with large energy spreads lead to higher equilibrium vacancy concentration and faster vacancy diffusion via low-energy migration paths. Vacancies in TiVZrTa have weaker abilities to form large vacancy clusters and prefer to form small clusters, indicating excellent resistance to radiation swelling. The formation energies of different types of dumbbells in TiVZrTa show significant differences and have large energy spreads. The binding abilities of interstitials in TiVZrTa are weaker compared to that in pure Ta and V. In TiVZrTa, fast vacancy diffusion and slow interstitial diffusion result in closer mobilities of vacancies and interstitials, significantly promoting point defect recombination. We further studied the effects of short-range ordered structures (SROs) on defect diffusion and evolution. SROs in TiVZrTa can effectively lead to higher fractions of defect recombination and fewer surviving defects. Our findings provide a comprehensive understanding of the underlying mechanisms of the high irradiation tolerance in body-centered cubic HEAs with large lattice distortion and suggest SROs are beneficial microstructures for enhancing irradiation tolerance.

Facile synthesis of anatase TiO2 nanoparticles using titanium metal and its enhanced photocatalytic activity under visible light

A green sol-gel method was employed to synthesize TiO2 nanoparticles (NPs) using titanium metal. The syn-thesized TiO2 NPs underwent comprehensive characterization using techniques including X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), and UV–Vis diffuse reflectance spectroscopy (UV-Vis DRS) to evaluate their structure, morphology, and spectral properties. By adjusting the amount of oxalic acid, tailored physico-chemical properties of anatase TiO2 catalysts were achieved. The obtained TiO2 catalysts demonstrated a high surface area, excellent absorption, and remarkable photocatalytic degradation of methylene blue under visible light irradiation. This enhancement is primarily contributed by the large surface area and oxygen vacancies.

Low-temperature and high-response NO2 sensor based on oxygen vacancy-enriched ZnO tubes inherited from waste chestnut mesocarps

Herein, we reported a low-cost ZnO biomorphic material used for low-temperature and high sensing detection of trace NO2. It was simply prepared by calcining Zn(NO3)2 solution soaked waste chestnut mesocarp biotemplate at 600 °C in air for the first time. The morphology of ZnO-6 material displays one-dimensional (1D) tubular structure assembled from uniform nanoparticles, and it has small mesopore distribution, relatively large specific surface area and abundant oxygen vacancy defects. The synergy of above advantageous factors provides a convenient channel for gas diffusion, and increases the surface active sites for adsorption and chemical reactions, which in turn efficiently enhances sensing performance of ZnO material towards NO2. At 92 °C, ZnO-6 sensor achieves a high response of 365 towards 10 ppm NO2, which is 30.4 times than that (S = 12) of template-free ZnO-0 sample. Also, it is larger than most reported 1D ZnO-based NO2 sensors. This sensor still possesses fast recovery characteristic, low detection limit, and good moisture tolerance. Moreover, the improved NO2 gas-sensing mechanism is discussed in more detail.

Defect annealing in heavy-ion irradiated tungsten: Long-time thermal evolution of saturated displacement damage at different temperatures

Understanding the time-dependence of thermal evolution and recovery of displacement damage is of great significance for evaluations of material performance in harsh fusion environments. In this study, the long-time thermal evolution of irradiation-induced defects has been investigated in heavy-ion irradiated tungsten at doses above the saturation limit. Polycrystalline tungsten samples were irradiated with 6 MeV copper ions up to 0.6 dpa at room temperature, followed by a series of isothermal annealing experiments at 653 and 1123 K for 5000, 10000 and 20000 s, respectively. Annealing at both temperatures triggered the coevolution of interstitial and vacancy defects, causing changes in defect morphology, size and population statistics. The damage microstructure remained stable after 5000 s at 653 K. Subtle variations in defect density and size were found, indicating the quasi-thermal-equilibrium state of the damage microstructure. In this temperature regime, small defect clusters were depleted via annihilation and absorption, while large defect clusters and defect-impurity complexes were pinned by traps requiring further thermal activation. Pronounced time-dependence in defect evolution was found at 1123 K. Defect recovery and defect coarsening became more prominent with increasing duration. Almost all dislocation networks dissociated into individual dislocation lines after 20000 s, while nano-sized voids and loops became fewer but gained an increase in size. These findings can be attributed to the collective impact of the increasing mobility of small vacancy clusters, the continual dissociation of large vacancy clusters and small voids, and the thermally activated detrapping of defect clusters from impurities and/or other traps.

Facile Fabrication of ZnO Nanoparticles for efficient dye degradation: Effect of Adipic Acid in photocatalytic activity

AbstractPhotocatalysis is the most environmentally benign and efficient method for degrading organic dyes in water purification. Herein, the synthesis of ZnO nanoparticles was achieved by simple homogeneous chemical precipitation via the support of adipic acid and followed the calcination process at elevated temperatures. Based on the physical and morphological characterization analysis, the high crystallinity hexagonal structure with uniform granular shape morphology of the ZnO nanoparticles was formed with a band gap of 3.2 eV. The photocatalytic performance of the ZnO nanoparticles was investigated with the degradation of methylene blue (M.B.) dye as a model compound in an aqueous medium under UV light irradiation. The optimal ZnO‐700 nanoparticles demonstrated the highest photocatalytic activity thanks to their large surface area and numerous oxygen vacancies. More importantly, a small amount of photocatalyst (0.4 g/L) successfully degraded M.B. dye from an aqueous solution with 100 % efficiency within just 11 minutes of irradiation time under UV light with protective photocatalytic activity 4 sequential cycles. Besides, in‐depth photocatalysis experiments present that via a facile two‐step synthesis method, the as‐prepared ZnO photocatalysts depict enhanced chemical stability in a harsh environment and efficient photodegradation.

Ultrafine, Dual-Phase, Cation-Deficient PrBa0.8Ca0.2Co2O5+δ Air Electrode for Efficient Solid Oxide Cells.

Nanostructured air electrodes play a crucial role in improving the electrocatalytic activity of oxygen reduction and evolution reactions in solid oxide cells (SOCs). Herein, we report the fabrication of a nanostructured BaCoO3-decorated cation-deficient PrBa0.8Ca0.2Co2O5+δ (PBCC) air electrode via a combined modification and direct assembly approach. The modification approach endows the dual-phase air electrode with a large surface area and abundant oxygen vacancies. An intimate air electrode-electrolyte interface is in situ constructed with the formation of a catalytically active Co3O4 bridging layer via electrochemical polarization. The corresponding single cell exhibits a peak power density of 2.08 W cm-2, an electrolysis current density of 1.36 A cm-2 at 1.3 V, and a good operating stability at 750 °C for 100 h. This study provides insights into the rational design and facile utilization of an active and stable nanostructured air electrode of SOCs.

The interactions between dislocations and displacement cascades in FeCoCrNi concentrated solid-solution alloy and pure Ni

Concentrated solid-solution alloys (CSAs) have been proposed as structural materials for advanced nuclear reactors due to their great irradiation tolerance. We studied and compared the interaction processes of displacement cascades and edge dislocations in FeCoCrNi CSA and pure Ni by molecular dynamics to explore the influence of dislocations on the irradiation resistances of CSAs. The edge dislocations preferentially absorb interstitials in both materials, however, the differences between the numbers of absorbed interstitials and vacancies in FeCoCrNi are smaller than in Ni, which is attributed to the smaller difference of mobilities of interstitials and vacancies in FeCoCrNi. When the centers of displacement cascades coincide with edge dislocations, the numbers of absorbed interstitials and vacancies in edge dislocations of FeCoCrNi are essentially the same, which is independent with PKA energies. The amounts of survived interstitials and vacancies in the matrix of FeCoCrNi are closer than that in pure Ni, which would avoid the formation of numerous large vacancy clusters induced by excessive vacancies. Furthermore, the edge dislocations are enriched with Ni, Co and depleted with Fe, Cr after interactions with displacement cascades, which is consistent with experimental results. The molecular dynamics simulation results of current study reveal that the edge dislocations in CSAs can probably serve as weak biased sinks for the annihilation of irradiation-induced defects and enhancing the irradiation resistances of CSAs.