Vacancy Defects Research Articles

High oxygen vacancy concentration and improved electrical conductivity in tetragonal LaNbO4 stabilized by Ga and Mo Co-doping on the Nb site

The LaNbO4-based materials were well documented to be good ionic conductors with the charge carriers of protons or interstitial oxygen ions. Herein, for the first time, we reported that the high oxide ion conduction, e.g. 3 × 10−3 S cm−1 at 900 °C, mediated by oxygen vacancies was achieved in LaNbO4 via equimolar Ga and Mo co-doping on the Nb site. Such a co-doping effectively stabilize the high temperature tetragonal structure of LaNbO4 to room temperature, and thus represents the first case of room temperature tetragonal LaNbO4 with high oxygen vacancy concentration, in contrast with the previously reported tetragonal LaNbO4 stabilized by isovalent doping free of oxygen vacancies or donor-doping with interstitial oxygen. The local structure and conducting mechanism of oxygen vacancy defects were thoroughly studied by computational simulations. The results revealed that the oxygen vacancy was accommodated by transforming two neighboring isolated NbO4 tetrahedrons into a corner-sharing Nb2O7 unit, and the oxygen ion migrated via a cooperative process involving the breaking and reforming of Nb2O7 units, assisted by synergic rotation and deformation of other neighboring NbO4 tetrahedra. These findings provided us a more comprehensive understanding for the LaNbO4-based materials and emphasized the possibility of developing LaNbO4 material as oxide-ion conductors mediated by high concentration of oxygen vacancies.

Multifunctional molecular bridge enabled interface passivation and strain release for stable and efficient all-inorganic perovskite solar cells

The precise management of the buried interface in n-i-p perovskite solar cells (PSCs) to achieve efficient charge extraction and transport is crucial for improving the photovoltaic performance. Here, a 4-chloro-2,5-dimethoxyaniline (CDA) modifier with multifunctional groups is utilized as a molecular bridge at the TiO2/CsPbBr3 buried interface to enhance the qualities of TiO2 and CsPbBr3 films and the arrangement of interface energy level. The chlorine atom in CDA can heal the oxygen vacancies defects on the TiO2 film surface, thereby improving its electron mobility and conductivity. The –O– and -NH2 groups in CDA play a passivation effect on the ions defects of CsPbBr3 film, and especially the two –O– groups can anchor the lattice Pb atoms of CsPbBr3 perovskite, which effectively reduce the trap states of CsPbBr3 film and release the residual lattice strain. The modification of CDA also improves the wettability and energy level of TiO2 film to optimize CsPbBr3 crystal growth and charge transport, respectively. Consequently, the CsPbBr3 PSCs with CDA molecular bridge free of encapsulation achieve a highly increased power conversion efficiency of 10.85%, in contrast with 8.16% value of the control device. After 720 h of storage at 85 °C and in air environment with 85% relative humidity, the efficiency of the CDA-modified device retains 93.1% of the initial value, demonstrating excellent long-term humidity and thermal stability.

Oxygen vacancy defect engineering in MoO2/Mo-doped BiOCl Ohmic junctions for enhanced photocatalytic antibiotic elimination

Vacancy defect engineering is an effective strategy for improving photocatalytic activity, but controlling surface vacancies precisely remains a challenge. In this study, MoO2/Mo doped BiOCl (Mo-BiOCl) composites enriched with oxygen vacancies (OVs) were prepared by a facile defect engineering strategy with MoO2 hollow spheres as a precursor and molybdenum sources, where the slowly released Mo4+ ions in the reaction system resulted in the tailored formation of Mo-BiOCl. The optimized MoO2/Mo-BiOCl composite (BOM-3) demonstrated significantly improved photocatalytic degradation efficiency for Tetracycline hydrochloride (TC) under visible light, with an apparent rate constant (k) 4.7 and 120 times higher than that of BiOCl and MoO2, respectively. The enhanced photocatalytic activity of BOM-3 can be attributed to the presence of abundant OVs, which extend the light response range by creating intermediate defect level from OVs. Additionally, the formation of ohmic heterojunction between Mo-BiOCl and MoO2 with close interface contacts facilitates rapid separation of interfacial charge carries and efficient migration of photogenerated electrons from Mo-BiOCl to MoO2. The possible degradation pathway of TC using BOM-3 is proposed, and toxicity evaluation indicates that most intermediates have lower toxicity than TC. This work presents a straightforward approach for improving photocatalytic antibiotic degradation through the construction of a novel Ohmic-junction with tuned surface OVs.

Sulfur vacancy riched pure 2H phase VS2 for efficient electrocatalytic hydrogen evolution

Vanadium disulfide (VS2), a typical metallic layered transition metal chalcogenide (TMC), has been widely concerned for its high electrical conductivity and reactivity in electrochemical energy storage and conversion applications. The 2H phase VS2 is expected to exhibit high electrocatalytic activity and be more stable for hydrogen evolution reaction (HER) than the 1T phase structure. But at present, there still lacks a facile method to prepare pure 2H phase VS2. Herein, we successfully prepared pure 2H–VS2 through a simple one-step low-temperature hydrothermal method. We have investigated the effect of the hydrothermal reaction conditions (including the proportion of raw materials and hydrothermal reaction temperatures) on the phase composition and microstructure. Under the optimal condition of 140°C-24 h with a vanadium sulfur ratio of 1:5, a nano-flower-like 2H–VS2 material with high crystallinity and rich sulfur vacancy defects was obtained. Leveraging these structural advantages, as a demonstration, the product exhibits excellent electrocatalytic HER activity (with η10 of 181 mV, Tafel slope of 52 mV dec−1, and J0 of 67.9 × 10−3 mA cm−2) and stability (it can continuously produce hydrogen for 20 h at a current density of 50 mA cm−2 with ultra-small increased potential of less than 5 mV). This work provides a new way for constructing atomic vacancy defects in layered TMCs for efficient electrocatalysis and is also expected to promote the research of the basic properties of high phase purity TMCs.

A crystal plasticity-based creep model considering the concurrent evolution of point defect, dislocation, grain boundary, and void

Creep poses a significant threat to the integrity and longevity of structural components at high-temperature. The most current understanding of creep mainly focuses on the coupled dynamics of point defects and dislocation, which may well describe the first and second stage of creep. However, the behavior of the three stages of creep is jointly controlled by point defect (vacancy) diffusion, dislocation glide, dislocation climb, grain boundary (GB) sliding, and void evolution. A critical knowledge gap still exists regarding how these different creep mechanisms are simultaneously coupled during the three stages of creep. In this work, a multi-physical mechanisms-based crystal plasticity model is proposed to consider the concurrent evolution of point defect, dislocation, GB, and void based on a unified thermodynamic framework. In-situ scanning electron microscope creep experiments and macroscopic creep experiments of Ti-6Al-4V were conducted to validate our model. The in-situ creep experiment directly revealed the GB sliding creep failure behavior of Ti-6Al-4V for the first time. The proposed model well predicts both the microscopic and macroscopic experimental behavior of creep. The contribution of different microstructure evolutions is discussed, and a phase diagram of the dominated creep mechanism is obtained. An in-depth analysis was conducted on the coupling effects and microstructure characteristics of different creep mechanisms. This work not only deepens our understanding of the micro creep mechanism but also offers valuable insights for designing materials with specific microstructures to enhance their creep resistance.

Multifunctional buried interface engineering via phenyl-phosphonic acid for efficient and stable SnO2-based planar perovskite solar cells

Tin dioxide (SnO2) is widely used as an electron transport layer (ETL) in efficient and stable perovskite solar cells (PSCs) due to its excellent optoelectronic properties and low-temperature solution preparation process. However, SnO2 ETLs fabricated by the conventional solution method have many defects, among which Sn dangling bonds (i.e., oxygen vacancies) are particularly prominent. Herein, a simple buried interface engineering is employed to introduce phenyl-phosphinic acid (PPA) into the surface of SnO2 film for the preparation of highly efficient PSCs. A series of test results have shown that the phosphate group (PO) in PPA can not only passivate oxygen vacancy defects on the surface of SnO2, but also improve the film-forming quality of the upper perovskite, thereby exhibiting better photoelectric conversion efficiency (PCE) and stability. Ultimately, the optimized device achieves a maximum PCE of 22.81 %, an improvement of about 15 % over the control device (19.82 %). Meanwhile, the nonencapsulated device based on SnO2-PPA ETL shows much better storage and light stability than the control SnO2.

Highly stoichiometry-deviating chalcopyrite quantum dots: synthesis and copper defects-correlated photophysical properties.

Copper indium selenide (CISe) is a prototype infrared semiconductor with low toxicity and unique optical characteristics. Its quantum dots (QDs) accommodate ample intrinsic point defects which may actively participate in their rather complex photophysical processes. We synthesize CISe QDs with similar sizes but with distinct highly stoichiometry-deviating atomic ratios. The synthesis condition employing Se-rich precursors yields the Cu-deficient CISe QDs with special photophysical properties. The photoluminescence exhibits monotonic red shift from 680 to 775 nm when the ratio of Cu's proportion to In's decreases. The luminescence is found to stem from the copper vacancy and antisite defects. The CISe QDs exhibit Raman activity at 5.6, 6.9, and 8.7 THz that is separately assigned to Cu-Se and In-Se optical phonon modes and surface mode.

First-principles study of vacancy-impurity (C, N, O) interactions in vanadium

Abstract Interstitial impurities of C, N, and O typically exist in V and its alloys, which have significant effects on the structure and properties of the materials due to their strong interaction with the vacancies. In this study, the structure and energy properties of vacancy-impurity complexes in V are comprehensively investigated by first principles calculations. The effects of impurity concentration and temperature on the concentration distribution of the complexes were studied using statistical methods. The results showed that the Vac n X 2 complexes exhibit a high sequential binding energy. There is an evident mutual attraction between the vacancy and the O atom, and it has a higher affinity than the C or N atom. The simple defect complexes of Vac 1 X 1–2 have always been the most abundant type of complex defect in V. The trapping effect of vacancy on C, N, and O atom is very significant at low temperatures rather than at high temperatures. This study would broaden the understanding of vacancy-impurity interactions in vanadium and provide new insights into the influence of C, N, and O on vacancy defect concentrations.

First-principle calculations of the electronic structure and optical properties of β-Ga2O3 with various vacancy defects

In this work, the effects of five types of vacancy defects on the electronic, optical and thermodynamic properties of β-Ga2O3 were investigated using first-principle calculations. The findings revealed that oxygen vacancies were more prevalent than gallium vacancies, with tetrahedral gallium vacancies being easier to form than octahedral ones. Vacancy defects induced a shift in the energy bands towards the lower energy end, with gallium vacancies reducing the bandgap from 4.9 eV to 3.1 eV, while the effect of oxygen vacancies on the bandgap was negligible. Oxygen vacancies introduced deep impurity levels near the Fermi level, while gallium vacancies introduced shallow impurity levels, primarily due to contributions from O-2p, Ga-4s, and Ga-4p orbital electrons. The differential charge density diagrams illustrated that gallium vacancies had a more pronounced impact on electronic distribution compared to oxygen vacancies, with VO3 exhibiting the least influence. As the temperature increases, the β-Ga2O3 with VO1 and VO2 exhibit higher thermodynamic stability compared to the intrinsic β-Ga2O3 and the one with VO3, while the intrinsic β-Ga2O3 has a superior heat capacity value compared to the β-Ga2O3 containing the five vacancy defects. The defect energy levels resulting from vacancies enhanced light absorption and conductivity, particularly oxygen vacancies, which improved the absorption capacity of β-Ga2O3 in the visible light range. These findings provide valuable insights for elucidating optical absorption experimental phenomena and photoluminescence.

Surface chemical polishing and passivation minimize non-radiative recombination for all-perovskite tandem solar cells

All-perovskite tandem solar cells have shown great promise in breaking the Shockley–Queisser limit of single-junction solar cells. However, the efficiency improvement of all-perovskite tandem solar cells is largely hindered by the surface defects induced non-radiative recombination loss in Sn–Pb mixed narrow bandgap perovskite films. Here, we report a surface reconstruction strategy utilizing a surface polishing agent, 1,4-butanediamine, together with a surface passivator, ethylenediammonium diiodide, to eliminate Sn-related defects and passivate organic cation and halide vacancy defects on the surface of Sn–Pb mixed perovskite films. Our strategy not only delivers high-quality Sn–Pb mixed perovskite films with a close-to-ideal stoichiometric ratio surface but also minimizes the non-radiative energy loss at the perovskite/electron transport layer interface. As a result, our Sn–Pb mixed perovskite solar cells with bandgaps of 1.32 and 1.25 eV realize power conversion efficiencies of 22.65% and 23.32%, respectively. Additionally, we further obtain a certified power conversion efficiency of 28.49% of two-junction all-perovskite tandem solar cells.

In-situ laser surface remelting of laser powder bed fused AlSi10Mg alloy at argon and nitrogen protective gases: Multiscale analysis

In the recent decades, laser powder bed fusion (LPBF) of aluminum alloy has been widely used in many fields. However, the poor surface quality, inevitable defects, and limited mechanical performance are obvious obstacles. In-situ laser surface remelting (LSR) is a promising method to give a second opportunity for the defect elimination. In this work, the LSR protective gas (argon and nitrogen) on the surface roughness, porosity, and microstructure of LPBF-fabricated AlSi10Mg alloy are experimentally compared. The nitrogen shows significant superiority in the surface flatness and densification enhancement compared with argon gas. After LSR at nitrogen gas, the average grain size reduces by 8.7 % and the low-angle grain boundaries increases from 70.9 % to 99.7 %. Moreover, a two-dimension mesoscale FEM (Finite Element Method, FEM) model is established to investigate the movement of multi pores inside the molten pool. Attributed to the lower density and dynamic viscosity and larger thermal conductivity, the combination of multi pores is significantly drastic with obvious surface fluctuation during LSR at nitrogen gas. According to the density functional theory (DFT) calculation, the absolute adsorption energies of nitrogen on Al (100) and Al (110) surfaces are generally larger, revealing that the argon gas is easier to be adsorbed on the processing aluminum layer during LSR treatment. Furthermore, the vacancy defects in the aluminum layer play positive roles in the adsorption of gas. This work establishes the importance of the protective gas on the LSR treatment, and provides a multiscale analysis method for the pore evolution.

Vacancy defect in boron nitride nanotube improves CO2 uptake from the gaseous mixture

Boron Nitride Nanotubes (BNNTs), 1-D nanomaterials, having extraordinary mechanical properties, are similar to carbon nanotubes. The structure of BNNT consists of alternative boron and nitrogen atoms, arranged in hexagonal lattice. In the current study, we have investigated the defected boron nitride nanotube (defBNNT) capability to capture CO2 from a mixture of greenhouse gases such as CH4, CO2, CO, and H2. The deep understanding of analytes@defBNNT complexation is acquired by interaction energies, quantum theory of atoms in molecules (QTAIM), noncovalent interaction (NCI), natural bond orbital (NBO), and frontier molecular orbital (FMO) analysis etc. It is evident from the results of interaction energies that all the analytes are physiosorbed over the defBNNT. The observed interaction energies are in the range of −2.09 to −6.43 kcal/mol. All the topological parameters, in QTAIM analysis, show that analyte@defBNNT complexes are stabilized through non-covalent interactions, particularly van der Waal's interactions. Results obtained from NCI analysis are strongly corroborated with the QTAIM analysis. The case of CO@defBNNT gives the highest charge transfer (0.031 e−), in natural bond orbital (NBO) analysis. Overall, there is a transfer of charge from analyte to the surface. Through electron density difference (EDD) analysis, the results of NBO charge transfer are also confirmed. We firmly believe that these findings could help experimentalists to design a well-suited surface for CO2 capture using defective boron nitride nanotubes (defBNNTs).

Investigating the dielectric and ferromagnetic behaviour of Ni and Co dual doped ZnO for diluted magnetic semiconductor

Herein, Ni/Co co-doped ZnO nanoparticles (NPs) were successfully prepared via chemical co-precipitation process. The structural, purity and crystallite size of as-prepared particles were confirmed by using x-ray diffraction (XRD). The results revealed the hexagonal wurtzite structure of ZnO without any impurity phase of as-prepared samples. The crystallite size decreased from 34.9 to 9.6 nm, whereas lattice strain reduced to 0.00086. The change in crystallite size, lattice parameters, strains and dislocation density further indicates the successful incorporation of dopants in ZnO host lattice. The dielectric properties, ac conductivity, and magnetic behaviour were steadily examined. The dielectric constant has been found to be 1070 with 5wt% at low frequency and become constant at higher frequency. It was revealed that dopant additions lead to attain high dielectric constant and low loss possibly attributed to interface polarization, and dipole polarization due to oxygen vacancy defects. M-H measurement observed that ferromagnetism at room temperature pure and doped ZnO samples. The ferromagnetic behaviour of pure ZnO NPs with Ms = 0.17 emu g−1, Mr = 0.11 emu g−1 and Hc = 67 which was increased to Ms = 0.85 emu g−1 and Mr = 0.65 emu/g for 5wt% Co. This improvement with increasing Co concentration indicates that oxygen defects may stabilize the ferromagnetic order. These interesting features encouraging to use this material for ultrahigh dielectric materials and spintronics.

Synergistic effects of vacancy and doping at Ge sublattices on the electronic and magnetic properties of new Janus Ge2PAs monolayer

Recently, 2D materials based on IV-V group have attracted great attention because of their interesting physical properties. In this work, Janus Ge2PAs monolayer with good stability is predicted using first-principles calculations. Our simulations assert its non-magnetic semiconductor nature with an indirect band gap of 1.11(1.75)eV obtained by PBE(HSE06)-based calculations. Further, vacancy defects and doping with transition metals (TMs = Cr and Mn) are explored in order to induce novel physical aspects. It is found significant magnetization of Janus Ge2PAs monolayer induced by Ge vacancies with total magnetic moments between 1.58 and 1.97 μB, where magnetism is produced mainly by atomic species around the defect sites. Herein, single Ge vacancy metalizes the monolayer, while the half-metallicity is obtained by creating a pair Ge vacancies. Regardless doping site, feature-rich diluted magnetic semiconductor and half-metallic behaviors are also obtained in Janus Ge2PAs monolayer by doping with Cr and Mn atom, respectively. In these case, TM impurities originate mainly the system magnetism with total magnetic moments between 2.00 and 3.03 μB. In addition, the coexistence of Ge vacancy and doping is also investigated. The calculated spin density shows an antiparallel spin orientation of Cr dopant and its neighboring atoms, meanwhile a parallel spin orientation is observed for Mn impurity and its neighboring atoms. Consequently, small total magnetic moment of 0.53 μB is obtained by the synergistic effects of doping with Cr and Ge vacancy, meanwhile the coexistence of Mn dopant and Ge vacancy generates a larger value of 4.88/4.89 μB. In all cases, the origin of electronic and magnetic properties is unraveled. Our results introduce new prospective spintronic 2D materials made from a new Janus Ge2PAs monolayer.

Surface reconstruction of defect-engineered MIL-88@Fe2O3 p-n heterojunction for enhanced electrocatalytic water and urea oxidation

Defective p-n heterojunction engineering has been under the spotlighted as a promising strategy for electrochemical oxygen evolution reaction (OER) and urea oxidation reaction (UOR). Still, it remains a great challenge how to use the space-charge region of p-n heterojunction to study the regulation mechanism of the p-n heterogeneous interface and vacancy defects on the incomplete self-reconstruction from pristine materials to (oxy)hydroxides. Herein, NH2-MIL-88b(Fe)/α-Fe2O3 p-n heterojunction with rich oxygen vacancies (denoted as p-n MIL-88@Fe2O3-OV) has been prepared using a simple one-step solvothermal method. The prepared catalyst exhibits promising electrocatalytic performance for OER and UOR, requiring low potentials of 1.50 and 1.35 V to reach the current density of 10 mA cm−2, respectively. The combined in-situ/ex-situ experimental and theoretical investigations unveil that p-n heterojunction engineering can not only facilitate charge transfer from n-type α-Fe2O3 to p-type NH2-MIL-88b(Fe) (denoted as MIL-88) and generate abundant oxygen vacancies, but also appreciably trigger phase transformation of MIL-88 into active FeOOH. The reconstructed FeOOH/α-Fe2O3 heterojunction optimizes the bonding strength towards key oxygen-containing intermediates and boosts the intrinsic activity. This work provides new insight into the self-reconstruction effect in the p-n heterojunction for enhancing the OER and UOR catalytic activity.

A novel gas sensor based on ZnO nanoparticles self-assembly porous networks for morphine drug detection in methanol

Developing efficient drug-detecting technologies is critical to the fight against their related abuse and trafficking crimes. In the present work, a novel morphine detection device based on metal-oxide-semiconductor (MOS) gas sensors with low-cost, highly sensitive, and portable is designed and fabricated. The exclusive sensitive material, ZnO nanoparticles self-assembly porous networks (ZnO-N) with ample oxygen vacancies (OV) defects prepared by PVP-chelated precipitation followed by a chemical blowing calcination method, is decisive to morphine drug identification. OV defects can modulate the intrinsic electronic structure and endow ZnO-N with more suitable band structures for enhancing oxygen species adsorption and morphine molecules oxidation. The optimal ZnO-N-2 sensor exhibits positive linear relationship response values of 1.1–8.8 in the concentrations of 2–200 ppm toward the standard morphine drug sample at the optimal operating temperature of 250°C. More importantly, the homemade portable device equipped with the ZnO-N-2 sensor can accurately identify the morphine drug and perform early warning. This work innovatively demonstrates the feasibility of MOS gas sensors for the detection of stashing morphine drugs in methanol, which is of great significance for effectively combating global drug-related crimes.

Revealing the role of oxygen on the defect evolution of electron-irradiated tungsten: A combined experimental and simulation study

The evolution of Frenkel pairs has been studied experimentally and theoretically in tungsten, a Body-Centered Cubic metal. We used positron annihilation spectroscopy to characterize vacancy defects induced by electron irradiation in two sets of polycrystalline tungsten samples at room temperature. Doppler Broadening spectrometry showed that some positrons were trapped at pure single vacancies with a lower concentration than expected. At the same time, positron annihilation lifetime spectroscopy revealed that positrons are annihilated in unexpected states with a lifetime 1.44–1.64 times shorter than that of single vacancy (200 ps), namely unidentified (X) defects. Secondary ions mass spectrometry detected a significant concentration of oxygen in these samples, of the same order of magnitude as electron-induced single vacancy. In addition, Cluster dynamics simulated defect behaviors under experimental conditions, and Two-component density functional theory was used to calculate defect annihilation characteristics that are difficult to obtain in experiments. Finally, by combining the theoretical data, we simulated the positron signals and compared them with the experimental data. This enabled us to elucidate the interactions between oxygen and Frenkel Pairs. The X defects were identified as oxygen-vacancy complexes formed during irradiation, as oxygen is mobile in tungsten at room temperature, and can be trapped in a vacancy, while its binding to self-ion atoms leads to their immobilization thus reducing defect recombination. Therefore, we anticipate oxygen to play an important role in the evolution of tungsten microstructure under irradiation.

Enhanced activation of peroxymonosulfate with cobalt-doped manganese-iron oxides for contaminant degradation: Regulation of oxygen vacancy defects

Peroxymonosulfate (PMS) based on heterogeneous catalytic reaction was a promising advanced oxidation process (AOP) to remove refractory contaminants. However, the contaminant degradation efficiency was challenged by the limited number of catalytic active site and low capacity for durable electron transfer. In this study, cobalt-doped manganese-iron oxides (CoxMn1-xFe2O4) rich in oxygen vacancy (Ov) were synthesized using a microwaved hydrothermal method and applied to activate PMS for bisphenol A (BPA) degradation, which achieved the complete removal of BPA within 30 min. In all samples, Co0.5Mn0.5Fe2O4 exhibited good catalytic activity for PMS, which was approximately 21.10 times higher than that of MnFe2O4. The results of density functional theory calculations and in-situ characterization demonstrated that the enhanced performance was ascribed to the generation of Ov and the enrichment of active site, which significantly accelerated the cycling of redox pairs and improved the PMS adsorption, which was more favorable to the formation of active specie in the electron transport process. The oxidation process involved both free radical and non-radical mechanisms, with main reactive species of O2−, and 1O2 being responsible for BPA degradation. In addition, the effects of different aqueous matrices, the results of reusability experiments, and ecotoxicity assessment experiments demonstrated the viability of the Co0.5Mn0.5Fe2O4/PMS system for real sewage purification. This research revealed a structural regulation method to enhance the catalytic activity of the material and offered new perspectives on the engineering of rich Ov.

Oxygen-vacancy-enriched CuMn2O4@CoAl layered double hydroxide nickel foam serving as a sophisticated electrode material for asymmetric supercapacitors

CuMn2O4, the abundant spinel in the earth, is considered a promising electrode material in the fields of energy storage and conversion, its practical application are hindered by limitations such as the insufficient energy density and poor stability of the material. Here, CuMn2O4@CoAl layered double hydroxide nickel foam (CuMn2O4@CoAl LDH NF) with abundant oxygen vacancy was constructed applied as an electrode material by simple hydrothermal method and NaBH4 reduction. The electrochemical tests validate that CuMn2O4@CoAl LDH NF soaked in NaBH4 solution stirring for 0.5 h (donated as CuMn2O4@CoAl LDH NF-0.5) shows a remarkable specific capacitance of 1437.7 F · g−1 at the current density of 1.0 A · g−1. The capacitance retention remains 86.1 % even after enduring 5000 cycles at a higher current density of 8.0 A · g−1. Furthermore, the assembled CuMn2O4@CoAl LDH NF-0.5// activated carbon (AC) supercapacitor exhibits a capacitance of 167.5 F · g−1, achieving a maximum energy density of 52.44 Wh · kg−1 and a power density of 4029.5 W · kg−1 when operated at the current density of 1.0 A · g−1. The experimental results show that the prepared material has excellent conductivity, good chemical stability, remarkable specific capacitance, and stable cycle life as a supercapacitor electrode. All these results confirm that both the construction of CuMn2O4@CoAl LDH core-shell structure and the reduction of NaBH4 can introduce abundant oxygen vacancy defects in CuMn2O4@CoAl LDH NF, which can significantly improve the electrical conductivity and accelerate the redox kinetics.

Transition metal in-situ doped BiOBr: Introducing oxygen vacancies to enhance hydroxyl radical generation for improved photocatalytic degradation of toluene

Photocatalytic oxidation for the removal of volatile organic compounds (VOCs) is one of the most effective and environmentally friendly means, and hydroxyl radicals with strong oxidation ability play an important role in the photocatalytic degradation of VOCs. In this paper, by selecting different transition metals (M=Co, Ni, Cu, Fe) for in situ doping modification of layered bismuth bromide oxide (BiOBr). It was found that among the catalysts Co-doped BiOBr had the highest photocatalytic degradation efficiency and mineralization rate (with 81.7 % and 64.0 %, respectively), and were significantly higher than those of BiOBr (with 51.4 % and 19.4 %, respectively). Experimental results and theoretical calculations confirmed that transition metal in situ doping modification can induce the generation of oxygen vacancy defects, while being more favorable to the adsorption and activation of H2O molecules, which leaded to the generation of a large number of hydroxyl radicals with stronger oxidative capacity and achieved the efficient photocatalytic degradation of toluene.