Vacancy Production Research Articles

In-situ fabrication of defect rich Cu2+1O on electrodeposited Cu cone arrays for promoting electrocatalytic anode hydrogen production

The low-potential formaldehyde oxidation reaction (FOR) is a significant replacement for oxygen evolution reaction, as FOR can couple with the cathode hydrogen evolution reaction (HER) to obtain a bipolar H2 production system with an extra low cell voltage. Cu-based electrocatalysts offer cost advantages in FOR but suffer from poor intrinsic activity and stability. Herein, a novel defect rich CF-Cu@Cu2+1O/Cu pinecone-shaped array electrocatalyst is fabricated by in-situ solution immersion of electrodeposited Cu cone arrays on foam for efficient and stable formaldehyde selective oxidation reaction to co-produce hydrogen and valuable formate. Benefitting from the partially mixed Cu2+1O in metallic copper and concomitant production of defect rich oxygen vacancies, only 0.04 VRHE is required for electrocatalytic FOR at 100 mA·cm−2 under alkaline conditions. FOR current density of CF-Cu@Cu2+1O/Cu electrode exhibits 2.35 times than that of CF-Cu (144 mA·cm−2) and 77 times than that of copper foam (4.4 mA·cm−2) at 0.5 VRHE. Moreover, the special pinecone-shaped structure is constructed to modify Cu-based catalysts with substantially enhanced stability. A FOR-HER co-electrolysis device of CF-Cu@Cu2+1O/Cu(+)||Pt/C(−) can achieve bipolar H2 production with an approaching 200 % Faradaic efficiency, requiring an extremely low electrical energy consumption of only ∼ 0.35 kWh per m3 of H2 and potential of 0.291 V at 100 mA·cm−2 at room temperature.

Enhanced photocatalytic performance of TiO2 with tunable oxygen vacancies induced by H2/N2 mixture treatment

Surface treatment can effectively modulate the surface properties of a photocatalyst to hasten the separation and transfer of photoinduced charges, ultimately achieving high photocatalytic performance. Herein, surface treatment of anatase-phase TiO2 prepared by a hydrothermal method was performed under H2/N2 mixed atmosphere. The experimental results demonstrate that roasting TiO2 in a H2/N2 atmosphere can effectively reduce partial Ti4+ to Ti3+, thereby facilitating the production of tunable oxygen vacancies (OVs) by disrupting Ti-O-Ti bonds. OVs can construct defective energy levels to bring about a decrease in the bandgap of TiO2 and an extension of light absorption range. Moreover, OVs remarkedly improve the separation of photoinduced charges of TiO2 and accelerate the photocatalytic reaction as active sites. The photocatalytic experimental results demonstrate that TiO2 exhibits the highest performance when roasting TiO2 in a H2/N2 atmosphere for 2 h, and the photocatalytic degradation rate constant of rhodamine B (RhB) and tetracycline (TC) on this sample under simulated solar light irradiation is 2.24 and 1.11 times higher than that on the reference TiO2, respectively. These findings provide valuable insights for designing highly efficient photocatalysts for effective water pollution treatment.

Optimization of carrier mobility in Pr-doped SrTiO3 thin films through controlled Sr-segregation for optoelectronic applications

Functional oxides employed in electronic components hold significant promise for future electronic devices. Strontium titanate based thin films have several emergent features due to unsaturated bonds, dimension restriction, production of oxygen vacancies and point defects that make them attractive for optoelectronic applications. Here we prepared Pr-doped strontium titanate thin films via RF magnetron sputtering in a pure Argon environment at various gas pressures followed by heat treatment. The structural parameters, analyzed via XRD and Raman spectroscopy, were correlated with the electrical transport properties. Intriguing morphological features such as Stranski–Krastanov (SK) growth and cation segregation observed by FESEM and AFM analysis were further examined to elucidate the conduction mechanism in the films. The optical studies unveiled significant transparency in the visible spectrum. Photoluminescence emission studies at specific wavelengths shed light on the involvement of oxygen vacancies. By carefully controlling annealing conditions and optimizing sputtering parameters, thin films devoid of Sr segregation with highest reported carrier mobility of 33.9 cm2/V s were prepared. The high mobility leading to enhanced conductivity render the films suitable for a wide range of optoelectronic applications.

Experimental subshell vacancies in a multiply ionised Sn atom by heavy ion impact

The adoption of Heavy Ion PIXE for elemental quantification remains limited by the lack of fundamental atomic parameters needed for the calculation of X-ray production cross section data. Widely adapted theoretical models used for approximating ionisation cross sections, as well as other atomic physical parameters such as X-ray fluorescence yields, are calculated based on single-hole vacancy production post ion-atom impact. This renders the use of conventional ‘protonic’ models invalid for heavy ion-atom collisions. The degree to which Multiple Ionisation (MI) manifests in different heavy ion-atom collision symmetries significantly modifies atomic physical parameters. This is due to the significant number of introduced spectator vacancies in higher subshells, especially where near-symmetry is approached and MI is more pronounced. Knowledge of the mean number of vacancies in upper subshells is thus important for modifying atomic parameters that are needed for the translation of ionisation to X-ray production cross sections. In the present study, MI effects for Sn L-shell X-rays were studied using characteristic X-ray energy shifts measured using a standard PIXE spectrometer induced by Si, Cu and I projectile ions with incident energies up to 0.75 MeV/u. MI satellite distributions were studied using a Wavelength dispersive X-ray spectrometer (WDS) for high resolution PIXE, induced by C and Si projectile ions with incident ion energies up to 1.25 MeV/u. The mean number of subshell vacancies in the M- and N- shell for energy shifted Sn Lα X-ray lines were determined using both standard and high resolution PIXE spectrometers.

Unveiling the promoting mechanism of Mo on the performance of CuCeOx catalyst for simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

NOx and CO coexisted in numerous actual industrial flue gases. The simultaneous removal of NOx and CO had great potential for application but remained still a challenge. Herein, a series of Mo-modified CuCeOx catalyst was developed to simultaneously achieve NH3-SCR denitration and CO oxidation. The results indicated that the CCM3 catalyst displayed the optimal performance with 91.2 % NOx conversion and 100 % CO conversion as well as excellent long-time stability and SO2 or/and H2O tolerance at 225 ℃. It was found that the strong interaction between Cu, Ce and Mo oxides resulted in the particles highly dispersed with smaller size on catalyst surface, which could provide abundant active sites to decreasing the competitive adsorption among reactive gases. Furthermore, the Mo modification promoted the production of more oxygen vacancies, Ce3+ and Oα species, which facilitated the redox recycle and the generation of intermediates. Moreover, the H2-TPR and NH3/CO/O2-TPD analysis illustrated that the reducibility and the capacity for reaction gas adsorption and activation were enhanced, which improved low-temperature activity. The in situ DRIFTS experiment revealed that the E-R and L-H mechanism were existed in NH3-SCR process on CC and CCM3 catalysts. What’s more, the stronger acidity and strengthened E-R mechanism on CCM3 catalyst hindered the adsorption of SO2 and weakened the inhibition effect of competitive adsorption among SO2 and NO. Additionally, both surface lattice oxygen and chemisorbed oxygen could react with Cu+–CO species to produce CO2, the pathway obeyed L-H and MvK mechanism. This work may provide a novel strategy for the treatment of CO and NOx pollutants in industrial flue gas.

Parameterization of vacancy production rate in phase-field models of fission gas bubble evolution in nuclear fuel

Phase-field modeling has increasingly been used to study microstructural evolution in fission gas bubbles in nuclear fuel to improve understanding of fission gas release. To improve computational efficiency, often only vacancies and gas atoms are included as defect species. In this case, the net effects of vacancy and interstitial production, recombination, and biased sink absorption are included as a net vacancy source, or net vacancy source combined with an effective sink. However, there has been a lack of clarity on what parameter values should be used for these approaches to best match the more complete physical picture that includes interstitials and vacancies. Here, we compare a phase-field model of void growth to analytical models for the source-only and source plus sink approach to gain insight into how the phase-field models can be parameterized effectively. The source-only approach provides greater flexibility to match growth rates determined from the full vacancy-interstitial picture. A strategy was developed for determining the value of the net vacancy source term by comparing to an analytical model that includes vacancy and interstitial production, recombination, and biased sink absorption. This strategy can be used to parameterize phase-field models of fission gas bubble growth.

Application of the Point Defect Model to the Oscillatory Anodic Oxidation of Illuminated n-Type Silicon in the Presence of Fluoride Ions Using Electrochemical Impedance Spectroscopy

This work aims to provide insight into the oscillations occurring during the anodic electrooxidation of Si in fluoride-containing electrolytes using electrochemical impedance spectroscopy (EIS). The EIS measurements were conducted within less than a tenth of the oscillation periods allowing changes in the electrical properties of the silicon/oxide/electrolyte interfaces to be monitored during an oscillatory cycle. Application of the power law model to the experimental data revealed a significant change in resistivity at the oxide/semiconductor interface while the properties at the oxide/electrolyte interface remained constant and the oxide layer varied only by about 1 nm around an average value of about 4.9 nm. The application of the point defect model to the semiconductor/oxide/F−-containing electrolyte interface suggests that the oscillations are linked to the time delay between the production of oxygen vacancies at the Si/oxide interface and their consumption at the oxide/electrolyte interface.

Enhanced photocatalytic activity of green synthesized zinc oxide nanoparticles using low-cost plant extracts

Developing stable and highly efficient metal oxide photocatalysts remains a significant challenge in managing organic pollutants. In this study, zinc oxide nanoparticles (ZnO NPs) were successfully synthesized using various plant extracts, pomegranate (P.M), beetroot roots (B.S), and seder, along with a chemical process. The produced ZnO NPs were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–Vis), Field Emission Scanning Electron Microscope (FESEM), High-Resolution Transmission Electron Microscopy (HRTEM), and Surface Area. For all prepared samples, the results indicated that the composition of the plant extract affects several characteristics of the produced particles, such as their photocatalytic properties, energy bandgap (Eg), particle size, and the ratio of the two intensity (0 0 2) and (1 0 0) crystalline planes. The particle size of the produced NPs varies between 20 and 30 nm. To examine NPs' photocatalytic activity in the presence of UV light, Methyl Orange (MO) was utilized. The Eg of ZnO synthesized by the chemical method was 3.16 e. V, whereas it was 2.84, 2.63, and 2.59 for P.M, Seder, and B.S extracts, respectively. The most effective ZnO NPs, synthesized using Beetroots, exhibited a degradation efficiency of 87 ± 0.5% with a kinetic rate constant of 0.007 min−1. The ratio of the two intensity (0 0 2) and (1 0 0) crystalline planes was also examined to determine a specific orientation in (0 0 2) that is linked to the production of oxygen vacancies in ZnO, which enhances their photocatalytic efficiency. Furthermore, the increase in photocatalytic effectiveness can be attributed to the improved light absorption by the inter-band gap states and effective charge transfer.

Enhanced solar-driven photoelectrochemical water splitting of H/N co-doped TiO2: Role of defect states in a band gap reduction and promotion of charge transfer

Photoelectrodes based on reduced TiO2 are being extensively studied in the search for photocatalytic materials that can perform solar-driven water splitting and renewable hydrogen production. To date, substantial efforts have been devoted to understanding the microscopic mechanisms that underlie their photoelectrochemical (PEC) behavior, but this is a critical missing input to the Ti 3d carriers that govern the PEC activity. In this study the single and co-doping (N, H) in anatase TiO2 are prepared for PEC hydrogen production. The codoped photocathode delivers much better PEC performance from the enhanced solar light response and a fast electron pathway. Soft x-ray spectroscopy including x-ray absorption (XAS) and photoelectron spectroscopy (XPS) has been used to investigate the location and occupation of the defect levels from doping, through which the relevant engineered electronic properties in doped TiO2 are determined. It is shown that co-doping effectively produce the substitutional nitrogen in comparison with single doping. The Ti3+ defect states promoted by doping introduces localized Ti 3d-derived states below Fermi level (EF), resulting in a large reduction (approximately 1 eV) in the band gap of co-doped TiO2. The progressive production of oxygen vacancies eventually causes a surface band upward-bending induced electron transfer mechanism critical for charge separation. The present insights into defect chemistry and its determination to the electronic structure of co-doped TiO2 provide important guidance for using TiO2 in electrocatalysis and optoelectronics.

Investigation into the photothermal catalytic CO2 decomposition over CeO2 with different morphologies: Behaviors of oxygen vacancies

CO2 is a viable renewable energy source, as global CO2 emissions are perennially increasing. The decomposition of CO2 to CO and O2 through high-temperature cracking of metal oxides via a two-step thermochemical cycle has been an effective strategy to reduce CO2 concentrations in the atmosphere. However, this thermochemical cycle requires a high reaction temperature (1273 K). Hence, in this study, we investigated photothermal CO2 decomposition over three CeO2 catalysts with different morphologies: porous CeO2 nanosheets (2D-CeO2), cubic-shaped CeO2 (C-CeO2), and octahedral CeO2 (O-CeO2). The photothermal synergistic effect eliminated the necessity of high temperatures, where light illumination increased the generation of oxygen vacancies and electron transfer to promote CO2 decomposition. The maximum rate of CO production by 2D-CeO2 at 250 °C was 69 μmol g-1h−1, which is significantly higher than those of O-CeO2 (47 μmol g-1h−1) and C-CeO2 (19 μmol g-1h−1). However, no activity was observed in dark conditions, even at 250 °C. In-situ DRIFTS, quasi in-situ EPR, XPS, and Ar-TPD experiments revealed that light irradiation promotes the production of oxygen vacancies on the catalyst surface and generates the intermediate CO2•− species, which cleave the C=O bonds and CO2 conversion, while temperature promotes the adsorption of CO2 on the catalyst surface and facilitates electron transfer. DFT calculations revealed the differences in oxygen vacancy formation and CO2 adsorption among various exposed crystal facets of CeO2. These findings provide new avenues for CO2 decomposition based on the adsorption and activation of CO2 on metal oxide surfaces and the low-temperature synergistic photothermal effect.

Highly improved ionic conduction in reverse spinel structured CoAl2O4 and ZnO heterostructure through interfacial disordering

For ceramic fuel cells with low temperatures operation (LT-CFCs; 350°-550 °C), increasing the ionic conductivity and improving the oxygen reduction electrocatalytic activity response at low operating temperatures would be highly desired. This Study presents a novel semiconductor heterostructure composite with a competent electrolyte membrane for LT-CFCs. The composite comprises CoAl2O4 (CA) in a spine-like structure and wurtzite-structured ZnO. We have demonstrated a button-sized CFC under H2 and ambient air environment delivering a high power density of 835 mW-cm−2 at 550 °C, with potential operating up-to 400 °C. Compared to ZnO and CA alone, the CA-ZnO heterostructure composite has reduced oxygen vacancy production and activation energy, facilitating ion transport more quickly through the CA-Zn interface. Density functional theory (DFT) computations, photoelectron spectroscopy, U-visible, X-ray diffraction, and HR-TEM are the characterization techniques used to study the enhanced ionic conduction of the CA-ZnO heterostructure composite. These results imply that the heterostructure approach works better than the simple bulk structure for the electrolyte application of LT-SOFCs.

Interface modulation of AgBiO3 via BiOCl in situ growth: Simultaneously boosting O* and OVs production

Photocatalytic activity of the composite photocatalyst AgBiO3/BiOCl was examined after the interface of AgBiO3 was modified by growing BiOCl in situ and building heterojunction towards increasing reactive oxygen species (O*) and oxygen vacancy (OVs) production. The degradation of rhodamine B (RhB) revealed that the photocatalytic performance of the heterojunction structure of AgBiO3/BiOCl-x (x=0.05, 0.2, 2, 5) was significantly improved over that of AgBiO3 monomer, with the degradation effect of AgBiO3/BiOCl-2 reaching 99.6 % within 60 minutes and no significant decrease in performance after reuse (93 % degradation after four cycles). Similar experiments also used another contaminant, tetracycline hydrochloride (TC-HCl). Within 60 minutes, under visible light irradiation, the degradation rate of TC was 89.1 % and the degradation rate was 0.0367 min−1. The effects of catalyst addition, varied starting concentrations, and pH on RhB degradation were also studied. Furthermore, the free radical scavenging studies and chemical characterizations revealed that the principal reactive radicals functioning in the reaction system were h+, 1O2 and ‧O2-. Based on the findings, a potential catalytic mechanism for the synergistic degradation of RhB via photo-driven and chemical oxidation of AgBiO3/BiOCl heterostructures was postulated.

Tailoring Pr0.5Sr0.5FeO3 oxides with Mn cations as a cathode for proton-conducting solid oxide fuel cells

The traditional Pr0.5Sr0.5FeO3 (PSF) cathode is customized with Mn cations to generate the new Pr0.5Sr0.5Fe0.9Mn0.1O3 (PSFMn) cathode for proton-conducting solid oxide fuel cells (H-SOFCs). Compared to the PSF oxide, the new PSFMn has a reduced thermal expansion, making it more compatible with electrolytes. Furthermore, Mn-doping enhances oxygen vacancy production in PSF, as revealed by experimental and first-principle calculations. More crucially, doping Mn into PSF improves proton diffusion kinetics, resulting in quicker proton diffusion and surface exchange. As a result, the H-SOFC with the PSFMn cathode achieves an output of 1446 mW cm−2 at 700 °C, but the PSF cell only achieves fuel cell performance of 1009 mW cm−2. The fundamental cause of the increased cell performance is the significantly reduced polarization resistance, implying that using the Mn-doping strategy enhances the cathode kinetics of conventional PSF cathodes for H-SOFC.

Fe-doping on CaV2O6 for oxygen vacancy controlling lithium storage

Currently, alkaline earth metal vanadates as the anode materials for lithium-ion batteries (LIBs) are gradually sparking attention due to their low cost, environmental friendliness, high theoretical capacity and safety. However, their practical application is still hampered by the fast capacity degradation resulting from the prolonged cycling condition and intrinsic low electrical conductivity. Herein, single-crystal Fe-doped CaV2O6 is prepared via the low-temperature combustion synthesis route. The Fe-doping accelerates the generation of low-valence-state vanadium in CaV2O6–2%Fe, leading to the production of oxygen vacancies for maintaining electroneutrality. The versatile design of CaV2O6–2%Fe improves the electron conductivity and promotes the Li-ion diffusion rate based on the generated dual defects of interstitial atoms of Fe and oxygen vacancies accordingly. As expected, the CaV2O6–2%Fe electrode exhibits superior rate capacity of 96.6 mA h g−1 at 5 A g−1 and a remarkable capacity retention of 125.6 mA h g−1 after 1000 cycles at 1 A g−1. Additionally, the partial decomposition of CaV2O6 during the initial lithiation stage, and the formation of amorphous Li–V–O in the subsequent cycle can be used to depict the lithium storage mechanism of CaV2O6–2%Fe.

Predicting displacement damage for ion irradiation: Origin of the overestimation of vacancy production in SRIM full-cascade calculations

Ion irradiation and implantation have wide applications that demand accurate determination of displacement damage profile and distribution of implanted ion concentration. The prediction of vacancies is especially important to determine displacements per atom (dpa), the standard parameter of primary radiation damage in materials. However, significant discrepancies exist in estimations of vacancies between full-cascade (F-C) and quick calculation (Q-C) options in the popular computer code SRIM. This study inspected the SRIM code and a relatively new code called Iradina, which uses a similar methodology, to develop an understanding of the origin of vacancy overestimation in the F-C options for SRIM and Iradina. We found that the default values of thresholds (namely final energy in SRIM and replacement energy in Iradina) in displacement production calculations results in excessively large number of calculated vacancies and very few replacements. After conducting multiple calculations using SRIM, Iradina, and MARLOWE (all based on the binary collision approximation), a comparison of the results indicates that there is a shortcoming in the SRIM and Iradina F-C methodology for treating near-threshold collisions. This issue is responsible for the deficiency of replacements and excess of calculated vacancies in the SRIM and Iradina F-C results. Drawing on the principles of collision physics, we propose recommendations for modifying the source codes to address these issues.

A-Site Nonstoichiometric BaxCo0.4Fe0.4Zr0.1Y0.1O3-δ Cathode for Protonic Ceramics Fuel Cells.

Highly active triple (proton, oxygen-ion, and electron) conducting materials BaxCo0.4Fe0.4Zr0.1Y0.1O3-δ (BxCFZY, x = 0.9-1.1) were prepared and characterized as potential cathodes for protonic ceramic fuel cells (PCFCs) in this work. The crystal structure, oxygen vacancy concentration, electrical conductivity, oxygen ion transfer properties, and electrochemical performance of BxCFZY oxides were systematically evaluated. The electrical conductivity of BxCFZY decreases but oxygen vacancies increase with increasing Ba content, indicating that the charge compensation was mainly achieved by the production of oxygen vacancy rather than the increase in the valence of transition metal cations. The power density of 1170 mW cm-2 and the polarization resistance of 0.05 Ω cm2 were achieved at 700 °C for the anode-supported single cells with B1.1CFZY cathode, suggesting that the excess A site on the BxCFZY had a positive effect on the catalytic activity for the oxygen reduction reaction. Furthermore, the distribution of relaxation time (DRT) analysis method was adopted to determine the electrochemical processes of the cells with BxCFZY cathodes. The calculated results confirmed that the cell with B1.1CFZY cathode exhibited the optimum performance due to the best oxygen ion transfer properties in BxCFZY cathodes.

Electron donation promotes the dual activation of lattice oxygen and molecular oxygen: The Pt-Pd/CeO2 catalyst efficiently catalyzes toluene

Dual activation of molecular and lattice oxygen is an important step in the catalytic oxidation of volatile organic compounds. Herein, CeO2 was derived from MOF as an electron donor support to develop a co-catalyst with Pt-Pd alloy nanoparticles (Pt-Pd/CeO2). The Prepared Pt-Pd/CeO2 exhibits excellent catalytic activity towards toluene oxidation, showing a turnover frequency (TOF 0.26 s−1) higher than those of Pt/CeO2 (0.05 s−1) and Pd/CeO2 (0.02 s−1). Several in situ experimental techniques and density functional theory calculations have revealed that the introduction of Pd valence electrons can intensify the electronic metal-support interactions (EMSIs) effects of Pt-Pd/CeO2 catalysts, which can weaken the Ce-O bond, thereby promoting the production and circulation of lattice oxygen and oxygen vacancies, and modulating the d-band centre to enhance the adsorption and activation of reactants. This study presents a comprehensive investigation of toluene oxidation on alloy-supported catalysts, providing practical guidance for designing reliable catalysts suitable for industrial applications.

Exploring the impact of surface oxygen vacancies on charge carrier dynamics in BiVO4 photoanodes through atmospheric pressure plasma jet post-treatment for efficiency improvement in photoelectrochemical water oxidation

We have demonstrated the production of high-density surface oxygen vacancy (ovs) in BiVO4 (BVO) photoanodes through the post-treatment of an atmospheric pressure plasma jet (APPJ). The 3.4-fold enhancement of photocurrent density of BVO photoanodes at 1.23 VRHE for photoelectrochemical (PEC) water oxidation due to 95 % of charge transfer efficiency at the BVO/electrolyte interface. In-situ transient absorption spectroscopy investigations provided insights into the charge carrier dynamics of the APPJ-treated BVO photoanode, revealing that abundant electrons could effectively be trapped in the ovs states to prevent charge carrier recombination. NiOOH/FeOOH oxygen evolution co-catalyst was further decorated on the APPJ-treated BVO photoanode resulted in a remarkable photocurrent density of 3.6 mA/cm2 at 1.23 VRHE, an anodic bias photon-to-current efficiency of 1.4 % at 0.62 VRHE, and a faradaic efficiency over 90 % in PEC water splitting. Our study provides important and novel insights into the surface vacancy engineering of metal oxides for green hydrogen production.

Low-Temperature Plasma-Assisted Catalytic Dry Reforming of Methane over CeO2 Nanorod-Supported NiO Catalysts in a Dielectric Barrier Discharge Reactor.

Nonthermal plasma (NTP)-assisted catalytic dry reforming of methane (DRM) is considered a powerful single-stage reaction mechanism because of its ability to activate normally stable CO2 and CH4 at a low temperature under ambient conditions. The thermodynamic barrier of DRM requires a high operating temperature (>700 °C), which can be reduced by nonequilibrium plasma. Herein, we present a method for the wet-impregnation synthesis of CeO2 nanorod (NR)-supported 5 and 15 wt % NiO catalysts for efficient NTP-promoted DRM with an applied power in the range of 24.9-25.8 W (frequency: 20 kHz), a CH4:CO2 feed gas ratio of 100:250 sccm, and a total flow rate of 350 sccm. The presence of NTP dramatically increased the reaction activity, even at 150 °C, which is usually inaccessible for thermally catalyzed DRM. The CH4 and CO2 conversion reaches a maximum of 66 and 48%, respectively, at 500 °C with the 15 wt % NiO/CeO2 NR catalyst, which are much higher than the values obtained for the 5 wt % NiO/CeO2 NR catalyst under the same conditions. According to the X-ray photoelectron spectroscopy profile for 15 wt % NiO/CeO2 NR, a higher concentration of NiO on CeO2 increases the proportion of Ce3+ in the catalyst, suggesting enhanced oxygen vacancy concentration with an increased amount of NiO loading. Additionally, a higher NiO loading promotes a higher rate of replacement of Ce4+ with Ni2+, which generates more oxygen vacancies due to the induced charge imbalance and lattice distortion within the CeO2 lattice. As a result, it can be inferred that the incorporation of Ni ions into the CeO2 structure resulted in inhibited growth of CeO2 crystals due to the creation of a NixCe1-xO2-α solid solution and the production of oxygen vacancies.

Oxygen Defect and Cl--Doped Modulated TiNb2O7 Compound with High Rate Performance in Lithium-Ion Batteries.

TiNb2O7 has attracted extensive attention from lithium-ion battery researchers due to its superior specific capacity and safety. However, its poor ion conductivity and electron conductivity hinder its further development. To improve the ion/electron transport of TiNb2O7, we report that chlorine doping and oxygen vacancy engineering regulate the energy band and crystal structure simultaneously through a simple solid-phase method. NH4Cl was used to realize Cl- doping and oxygen vacancy production. A Rietveld refinement demonstrates an effective substitution of Cl in the O sites of Nb-O octahedra, with an enlarged crystal plane spacing. The oxygen vacancies provide more active sites for lithium intercalation. The diffusion coefficient of Li+ is inceased from 2.39 × 10-14 to 1.50 × 10-13 cm2 s-1, which reveals the positive influence of Cl- doping and oxygen vacancies on the promoted Li+ transport behavior. Charge compensation is introduced by the doping of Cl- and the generation of oxygen vacancies, leading to the formation of Ti3+ and Nb4+ and the adjustment of the electronic structure. DFT calculations reveal that TiNb2O7 with Cl- doping and an O vacancy shows a metallic property with a finite value at the Fermi level, which is conducive to electron transfer in the electrode material. Benefiting from these advantages, the modified TiNb2O7 presents superior rate performance with a commendable capacity of 172.82 mAh g-1 at 50 C. This work provides guidance to design high-performance anode materials for high-rate lithium-ion batteries.