Oxygen Vacancy Engineering Research Articles

Defect Engineering of Oxygen Vacancies in Ultrathin NiFe-Layered Double Hydroxides: Insights from Density Functional Theory

Defect Engineering of Oxygen Vacancies in Ultrathin NiFe-Layered Double Hydroxides: Insights from Density Functional Theory

Research Progress of and Perspectives of BiOCl Photocatalytic Materials

BiOCl is considered as a candidate to effectively separate photogenerated carriers due to its strong internal electronic field, thus being regarded as a new type of photocatalyst. We interpret BiOCl from the crystal structure, photocatalytic mechanism, synthetic method and influence factors of photocatalytic performance. In view of the shortages of inherent wide band-gap and high recombination probability photo-generated carrier for BiOCl, researches on how to improve the photocatalytic ability were summarized by the modification methods such as ion doping, noble metal deposition, heterojunction construction, morphology control and oxygen vacancy engineering during synthesis. Finally, the future development trend of BiOCl was prospected.

Enhanced Electrocatalytic Oxygen Reduction Reaction of TiO2 Nanotubes by Combining Surface Oxygen Vacancy Engineering and Zr Doping.

This work examines the cooperative effect between Zr doping and oxygen vacancy engineering in anodized TiO2 nanotubes (TNTs) for enhanced oxygen reduction reactions (ORRs). Zr dopant and annealing conditions significantly affected the electrocatalytic characteristics of grown TNTs. Zr doping results in Zr4+ substituted for Ti4+ species, which indirectly creates oxygen vacancy donors that enhance charge transfer kinetics and reduce carrier recombination in TNT bulk. Moreover, oxygen vacancies promote the creation of unsaturated Ti3+(Zr3+) sites at the surface, which also boosts the ORR interfacial process. Annealing at reductive atmospheres (e.g., H2, vacuum) resulted in a larger increase in oxygen vacancies, which greatly enhanced the ORR activity. In comparison to bare TNTs, Zr doping and vacuum treatment (Zr:TNT-Vac) significantly improved the conductivity and activity of ORRs in alkaline media. The finding also provides selective hydrogen peroxide production by the electrochemical reduction of oxygen.

Flame Spray Pyrolysis Synthesis of Vo-Rich Nano-SrTiO3-x.

Engineering of oxygen vacancies (Vo) in nanomaterials allows diligent control of their physicochemical properties. SrTiO3 possesses the typical ABO3 structure and has attracted considerable attention among the titanates due to its chemical stability and its high conduction band energy. This has resulted in its extensive use in photocatalytic energy-related processes, among others. Herein, we introduce the use of Flame Spray Pyrolysis (FSP); an industrial and scalable process to produce Vo-rich SrTiO3 perovskites. We present two types of Anoxic Flame Spray Pyrolysis (A-FSP) technologies using CH4 gas as a reducing source: Radial A-FSP (RA-FSP); and Axial A-FSP (AA-FSP). These are used for the control engineering of oxygen vacancies in the SrTiO3-x nanolattice. Based on X-ray photoelectron spectroscopy, Raman and thermogravimetry-differential thermal analysis, we discuss the role and the amount of the Vos in the so-produced nano-SrTiO3-x, correlating the properties of the nanolattice and energy-band structure of the SrTiO3-x. The present work further corroborates the versatility of FSP as a synthetic process and the potential future application of this process to engineer photocatalysts with oxygen vacancies in quantities that can be measured in kilograms.

Mixed-Dimensional (2D/3D/3D) Heterostructured Vanadium Oxide with Rich Oxygen Vacancies for Aqueous Zinc Ion Batteries with High Capacity and Long Cycling Life.

Heterostructure engineering and oxygen vacancy engineering are the most promising modification strategies to reinforce the Zn2+ ion storage of vanadium oxides. Herein, a rare mixed-dimensional material (VOx), composed of V2O5 (2D), V3O7 (3D), and V6O13 (3D) heterostructures, rich in oxygen vacancies, was synthesized via thermal decomposition of layered ammonium vanadate. The VOx cathode provides an exceptional discharge capacity (411 mA h g-1 at 0.1 A g-1) and superior cycling stability (the capacity retention remains close to 100% after 800 cycles at 2 A g-1) for aqueous zinc-ion batteries (AZIBs). Ex situ characterizations confirm that the byproduct Zn3V2O7(OH)2·nH2O is generated/decomposed during discharge/charge processes. Furthermore, VOx demonstrates reversible intercalation/deintercalation of H+/Zn2+ ions, enabling efficient energy storage. Remarkably, a reversible crystal-to-amorphous transformation in the V2O5 phase of VOx during charge-discharge was observed. This investigation reveals that mixed-dimensional heterostructured vanadium oxide, with abundant oxygen vacancies, serves as a highly promising electrode material for AZIBs, further advancing the comprehension of the storage mechanism within vanadium-based cathode materials.

Theory and experiment on SERS sensitivity tuning of TiO2 aerogels based on surface oxygen vacancy engineering

The exploration of new and high-performance semiconductor substrates has always been one of the most important research directions in SERS technology. However, the low sensitivity of semiconductor SERS substrates limits their application. Herein, TiO2 aerogels with high surface oxygen vacancies were fabricated by sol–gel method followed by supercritical drying. Compared with traditional semiconductor materials, TiO2 aerogels exhibit low detection limits (1 × 10–7 M) for 4-mercaptobenzoic acid molecules. Moreover, density functional theory further revealed that abundant surface oxygen vacancies endow TiO2 aerogels with high electrostatic potential, which promotes the formation of stable surface charge transfer complexes and allows significant charge transfer from molecules to TiO2 aerogels. It is worth noting that the narrower band gap and higher electron density of states of TiO2 aerogels effectively enhance the vibrational coupling in the substrate-molecule system, leading to significant SERS activity of TiO2 aerogels.

Oxygen Vacancy Engineering of FeOx toward Oxygen-Tolerant Hydrogen Peroxide Reduction for Reliable Bioassays.

The accurate determination of hydrogen peroxide (H2O2), an important clinical disease relevant biomarker, is of great importance for the diagnosis and management of illnesses. By using the cathodic monitoring approach, H2O2 can be accurately detected because interfering signals from easily oxidizable endogenous and exogenous species in biofluids can be avoided. However, the simultaneous occurrence of the oxygen reduction reaction (ORR) restricts the practical use of this cathodic method. In this study, via oxygen vacancy modulation, we synthesized FeOx catalysts that can selectively reduce H2O2 over O2. The H2O2 detection system based on this catalyst exhibits an outstanding ORR inhibition ability. Furthermore, by integrating this catalyst with glucose oxidase, a model enzyme, a reliable bioassay system was developed that can selectively detect glucose over a wide variety of interferents in artificially simulated tissue fluids. The bioassay system employing this catalyst in conjunction with oxidases is generally applicable to accurate detect a wide range of biomarkers.

The Counterbalancing Role of Oxygen Vacancy between the Electrochromic Properties and the Trapping Effect Passivation for Amorphous Tungsten Oxide Films

Defect engineering of electrode materials is considered highly effective in regulating their performance, among which oxygen vacancies play a vital role. Thereupon, comprehensively understanding effects of oxygen vacancy in electrochemical processes of transition metal oxides stays hot and controversial, representatively for amorphous tungsten oxide films and their electrochromic (EC) behaviors. Upon long‐term cycling, amorphous tungsten oxide suffers from the universal trapping effect governed by the intrinsic host microstructure and transport kinetics of the inserted ions, implying that manipulating oxygen vacancies could be a potential solution to the ion‐trapping problem. Hence, systematic work is urgent for not only tackling the trapping effect but also understanding the effect of oxygen vacancies on EC behaviors. Herein, the concentration of oxygen vacancies in the amorphous tungsten oxide films is modulated over a wide range. In combination with comprehensive experiments and first‐principles calculations, the presence of oxygen vacancy is detrimental to the EC properties, but it greatly attenuates the trapping effect. Excellent cyclic stability is achieved with a 100% optical modulation rate and charge capacity retention after 5000 cyclic voltammetry cycles. This study elucidates understanding of oxygen vacancy engineering in transition metal oxides, particularly regarding trapping effect passivation.

Laser assisted oxygen vacancy engineering on Fe doped CoO nanoparticles for oxygen evolution at large current density

Exploring cost-effective non-noble metal-based catalysts with high activity and stability is of great significance for energy conversion and storage involving oxygen evolution reaction (OER). Here, we employed a laser irradiation technique to synthesis Fe doped CoO nanoparticles with ultrafine size (≈ 5.4 nm) and abundant oxygen vacancies (Fe-Ov-CoO). The ultrafine size of Fe-Ov-CoO nanoparticles provides more active sites to be exposed. Fe doping and oxygen vacancy promote the intrinsic activity and electron transfer rates of Fe-Ov-CoO, giving rise to high activity and stability catalyst for OER. Fe-Ov-CoO delivers a large current density of 1000 mA cm−2 at an overpotential of 548 mV, which is much better than commercial RuO2. Moreover, Fe-Ov-CoO presents a remarkable long-term stability with negligible degeneration at a high current density of 500 mA cm−2 for 120 h. This work provides a new route to develop OER electrocatalyst with high activity and stability.

Engineering oxygen vacancies on Tb-doped ceria supported Pt catalyst for hydrogen production through steam reforming of long-chain hydrocarbon fuels

Steam reforming of long-chain hydrocarbon fuels for hydrogen production has received great attention for thermal management of the hypersonic vehicle and fuel-cell application. In this work, Pt catalysts supported on CeO2 and Tb-doped CeO2 were prepared by a precipitation method. The physical structure and chemical properties of the as-prepared catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, H2 temperature programmed reduction, and X-ray photoelectron spectroscopy. The results show that Tb-doped CeO2 supported Pt possesses abundant surface oxygen vacancies, good inhibition of ceria sintering, and strong metal-support interaction compared with CeO2 supported Pt. The catalytic performance of hydrogen production via steam reforming of long-chain hydrocarbon fuels (n-dodecane) was tested. Compared with 2Pt/CeO2, 2Pt/Ce0.9Tb0.1O2 and 2Pt/Ce0.5Tb0.5O2, the 2Pt/Ce0.7Tb0.3O2 has higher activity and stability for hydrogen production, on which the conversion of n-dodecane was maintained at about 53.2% after 600 min reaction under 700 oC at liquid space velocity of 9 ml·(g cat)–1∙h–1. 2Pt/CeO2 rapidly deactivated, the conversion of n-dodecane was reduced to only 41.6% after 600 min.

Surface oxygen vacancy engineering of Cr-doped FeNi3/NiFe2O4 Mott-Schottky heterojunction as efficient electrocatalyst for high current density water oxidation

The defect engineering at the surface by filling of oxygen vacancies during OER causing surface reconstruction is considered to be a unique way to boost up intrinsic electrocatalytic activity, especially towards oxygen evolution reaction (OER) mechanism. The present study aimed creation of large number of oxygen vacancies by Cr-doping into FeNi3/NiFe2O4 Mott-Schottky heterojunction electrocatalyst causing much desirable surface engineering and electronic modulation in favour of OER activity. The optimized heterojunction nanoparticles exhibited an excellent catalytic activity with low overpotential of 246 mV at the current density of 20 mA cm−2 with low Tafel slope value of 55 mV dec−1 for OER. Such oxygen vacancy-aided surface reconstruction during OER demonstrated an outstanding durability over 200 h even at high current density of 1000 mA cm−2 in 1 M KOH electrolyte. The surface oxygen vacancy engineering with the help of ex-situ Raman spectroscopy at different anodic potentials reveals the filling of vacancies and generation of MOOH as surface reconstruction of electrocatalyst during OER, also supported by XPS, TEM and EELS analyses.

Evidence of oxygen vacancy-mediated ultrahigh SERS sensitivity of Niobium pentoxide nanoparticles through defect engineering: theoretical and experimental studies.

Oxygen vacancy engineering in metal oxide-based semiconductors has emerged as an important area of research for sensing applications, such as Surface-enhanced Raman scattering (SERS), gas sensing, etc. It has the potential to replace high-cost and unstable noble metal-based substrates in the near future. However, improving the SERS enhancement factor in semiconductor-based substrates remains a challenge. In the present study, we demonstrate that oxygen vacancy engineering in Niobium pentoxide (Nb2O5) enables ultrahigh SERS sensitivity. Oxygen vacancies were induced and manipulated in the Nb2O5 nanoparticles via a facile high-energy ball milling method and post-growth oxygen annealing. A high enhancement factor (EF) of 5.15 × 107 was obtained for the Methylene Blue (MeB) molecule on the oxygen-deficient substrate with the lowest detection limit of 10-8 M, which is 2 orders of magnitude lower than the pristine substrate. Through a careful analysis of the experimental data and theoretical calculations, we investigated the underlying mechanism behind the high EF in SERS and showed that the SERS performance is directly proportional to the oxygen vacancy concentration in the Nb2O5 nanoparticles. Density functional theory (DFT) calculation suggests a strong coupling of the vibronic states and an increased charge transfer (CT) efficiency in the Nb2O5-MeB complex mediated through the vacancy-induced trap states in the defective Nb2O5 structure. Finite element method (FEM)-based simulations revealed a field enhancement factor of ∼4.17 × 102 that contributed to the SERS EF, while the remaining is contributed to the oxygen vacancy-mediated charge transfer, i.e., a factor of ∼1.23 × 105 is due to the high CT efficiency, the highest among the reported values. We believe that these findings offer valuable insights into the fabrication of defect-tailored cost-effective semiconductor-based SERS substrates for ensuing applications, such as trace dye detection.

Deciphering the bridge oxygen vacancy-induced cascading charge effect for electrochemical ammonia synthesis.

Oxygen vacancy engineering has recently been gaining much interest as the charging effect it induces in a material can be used for varied applications. Usually, semiconductor materials act poorly in electrocatalysis, particularly in the nitrogen reduction reaction (NRR), owing to their inherent charge deficit and huge band gap. Vacancy introduction can be a viable material engineering route to make use of these materials for the NRR. However, a detailed investigation of the vacancy-type and its role for the structural reorientation and charge redistribution of a material is lagging in the field of NRRs. This work thus focuses on the synthesis of oxygen vacancy-engineered SnO2 with a gradual structural transformation from in-plane (iov) to bridge-type oxygen vacancy (bov) density. Consequently, the electron occupancy of the sp3d hybrid orbital changes, leading to an upshifted valence band maxima towards the Fermi level. This has a profound effect on the nature of N2 adsorption and the extent of NN bond polarization. Sn atoms adjacent to the bov are found to have a fair density of dangling charges that accomplish the NRR process at a comparatively low overpotential and determine the binding strength of the intermediates on the active site. The obscured yet stable reaction intermediates are thereby identified with in situ ATR-IR studies. A restricted hydrogen evolution reaction Faradaic on the Sn-site (favored over O-atoms) results in a Faradaic efficiency of 48.5%, which is better than that reported in all the literature reports on SnO2 for the NRR. This study thus unveils sufficient insights into the role of oxygen vacancies in a crystal as well as electronic structural alteration of SnO2 and the effect of active sites on the rate kinetics of the NRR.

Synergy of W doping and oxygen vacancy engineering on d-band center modulation for enhanced gas sensing performance

W doping and vacancy engineering allowed the control of the d-band center of the material and improved the gas sensing performance.

Oxygen vacancy engineering of ultra-small CuWO4 nanoparticles for boosting photocatalytic organic pollutant degradation.

Nanomaterials have attracted great interest in the field of photocatalytic degradation due to their larger specific surface area and efficient charge/mass transfer ability, which are beneficial for enhancing photocatalytic activity. However, the bandgap of photocatalysts would increase with the size reduction, weakening the photoabsorption ability. Thus the relationship between the size of catalysts and photoactivity should be balanced to achieve optimal photocatalytic performance. Herein, ultra-small CuWO4 nanoparticles (ca. 39 nm) with moderate oxygen vacancies (CuWO4-OVs) were synthesized by the cascade strategy (ligand confinement@fast calcination). The introduction of oxygen vacancies offset the deficiency of light absorption ability caused by the small size effect. Besides, oxygen vacancies could provide more reaction active sites, conducive to the adsorption and activation of dye molecules and H2O. Degradation experiments reveal that the optimized photocatalyst CuWO4-OVs 350 shows outstanding photocatalytic activity, and the removal ratio of methylene blue (MB) reaches over 90.26% in 70 min, exceeding that of pure CuWO4-air (37.66%). Additionally, the degradation performance of CuWO4-OVs 350 surpasses most of the other CuWO4-based photocatalytic systems. More importantly, the photocatalytic degradation activity of CuWO4-OVs 350 could remain at 88.26% even after five cycles, and high photostability was achieved. This work affords constructive inspiration for synergistic photoactivity enhancement and increase of catalyst reaction active sites to achieve eminent photocatalytic degradation performance.

Surface oxygen vacancy engineering in weak Bi–O bonded ferroelectric bismuth sodium titanate for boosting the photocatalytic CO2 reduction reaction

A novel ferroelectric photocatalyst modulated by the surface and polarization states is developed to promote the CO2 reduction reaction, and the lattice distortion and elemental coordination environment are elaborated in detail.

MOF-derived CeO2 catalysts with Pr doping: engineering oxygen vacancies for improved CO2 conversion to dimethyl carbonate

Pr-doped CeO2 from MOF templates exhibits enhanced catalytic performance for dimethyl carbonate synthesis from CO2 and methanol, driven by increased oxygen vacancies and improved acidic/basic properties.

High-performance Al-doped Cu/ZnO catalysts for CO2 hydrogenation to methanol: MIL-53(Al) source-enabled oxygen vacancy engineering and related promoting mechanisms

Innovative catalyst design and in-depth mechanism understanding are imperative for industrialization of CO2 hydrogenation to methanol. Herein, Al-doped Cu/ZnO catalysts, Cu/Al-ZnO-x (x = 1/32, 1/16 and 1/8, denoting Al/Zn molar ratio), were creatively synthesized using MIL-53(Al) as Al sources and reactive templates. The Cu/Al-ZnO-1/16 catalyst exhibited the highest methanol production rate among the Cu/Al-ZnO-x catalysts, which was 1.93 times as active as the conventional Cu/Al-ZnO-1/16-C catalyst using Al(NO3)3·9H2O as Al source. Structural characterizations reveal that the use of MIL-53(Al) led to higher SBET, more uniform Al distribution, more abundant oxygen vacancies, more appropriate metal-support interactions and larger amount of medium basic sites. Mechanism studies demonstrate that Al doping would markedly induce oxygen vacancy formation on Cu-ZnO interfaces and thus significantly boost methanol synthesis activity. This work offers a facile approach to develop efficient methanol synthesis catalysts and provides new insights into the nature of Al promotion in Cu/ZnO-based catalysts.

Exploring the role of oxygen vacancies on the magnetic and electromagnetic absorption properties of La3+-modified M-type hexaferrite with Al3+ doping

The demand for effective microwave-absorbing materials has recently surged due to rapid advancements in electromagnetic (EM) devices. Recently, engineering oxygen vacancies has also become one of the effective ways to develop efficient microwave-absorbing materials. So, understanding the EM absorption mechanism of these materials has become crucial for better engineering of such materials. This article investigates the magnetic properties along with the EM absorption mechanism of M-type hexaferrite, with optimal incorporation of rare-earth element La3+ and doping of transition metal Al3+ cation. The presence of La3+ ions at an optimal level promotes the reduction of Fe3+ to Fe2+ cations and creating oxygen vacancies to offset the electrical charge imbalance. This phenomenon impacts both the magnetic and EM characteristics of the materials. The presence of Fe2+ cations enhanced the spin-orbital interaction, resulting in a strong magnetic anisotropy field along the c-axis. The lowest reflection loss of −36.37 dB at 14.19 GHz, is observed with a bandwidth of 3.61 GHz below −10 dB for x = 0.6. These microwave absorption properties can be attributed to the adequate compensation between dielectric and magnetic losses, which arise from phenomena like dielectric relaxation, magnetic resonance, and conduction loss due to electron hopping between Fe3+ and Fe2+ with proper incorporation of the attenuating constant and excellent impedance matching, along with microstructure of the materials. Furthermore, the material’s exceptional absorption properties are also influenced by the rapid movement of oxygen vacancies from its interior to its surface when exposed to high frequencies, thereby impacting its conductivity. Therefore, it is believed that the regulation of oxygen vacancies can serve as a versatile strategy for developing materials with efficient microwave-absorbing capabilities.

Atomic ruthenium doping in collaboration with oxygen vacancy engineering boosts the hydrogen evolution reaction by optimizing H absorption

Development of cost effective and performance efficient catalyst for hydrogen evolution reaction (HER) holds great importance to advance a green future. In this work, atomic Ru doped NiMoO4 nanorod arrays with rich oxygen vacancy were tailor-synthesized on nickel foam. Both theoretical calculations and experiments elucidated the synergistic effects of Ru doping and oxygen vacancy engineering for the facilitating of H adsorption and water activation energy barrier reduction for water dissociation, which significantly enhanced the hydrogen evolution kinetics and thereby accelerated the water splitting process. The sample obtained exhibits a remarkably low overpotential of 49 mV at 10 mA cm−2 and a super robust stability, which is comparable to the performance of commercially available Pt/C and among one of the most efficient catalysts towards water splitting. Moreover, an integrated green energy-to-hydrogen device using sunlight, wind and thermal as the power sources was successfully built to prove the promising potential of the developed catalyst for the practical applications. This work provides a feasible strategy to prepare low-cost metal oxide electrocatalysts by noble element doping and oxygen vacancy engineering for efficient hydrogen evolution reaction.