Interfacial Oxygen Vacancies Research Articles

Abundant interfacial and intrinsic oxygen vacancies enabling small nickel/ceria nanocrystal efficient CO2 methanation

Smaller nano-sizes typically result in supported catalysts with abundant interfacial and intrinsic oxygen vacancies for better adsorption and activation of small molecules, including CO2, leading to improved efficiency of CO2 methanation. Here, Ni/CeO2-S with the smaller nano-size of around 4.2 nm is used to catalyze CO2 methanation, which exhibits significantly enhanced activity compared to larger nano-sized Ni/CeO2-L catalyst, even surpassing the most majority of previously reported catalysts using CeO2 as the support or Ni as the active metal. The coexistence of interfacial defects and intrinsic oxygen vacancies allows for enhanced adsorption and activation of CO2 molecules as well as H spillover, resulting in such improved CO2 methanation. In-situ DRIFTS demonstrate a nearly sole Formate pathway on Ni/CeO2-S for efficient CO2 hydrogenation. This research provides valuable insights into the reaction mechanism over a small nanosize supported catalyst.

Chemically bonded nonmetallic LSPR S-scheme hollow heterostructure for boosting photocatalytic performance

The light absorption, mass transfer, and charges separation are essential to the efficiency of photocatalytic reaction, but constructing photocatalyst with the three excellent properties is still challenging. Herein, the interfacial Mo-S bonds and oxygen vacancy synchronously decorated MoO3-x/Zn3In2S6 (MoO3-x/ZIS) heterostructure was rationally designed and synthesized. The oxygen-defective MoO3-x nanotubes showed hollow structure and local surface plasmonic resonance (LSPR) effect, which improved mass transfer and solar light absorption. Besides, the built-in electric field and interfacial Mo-S bond provided endogenetic impetus and channels for rapid photoexcited charge carriers transfer and separation. The photocatalytic hydrogen (H2) evolution and hydrogen peroxide (H2O2) production on optimal MoO3-x/ZIS composite were 17.34 and 4.47 mmol g−1 h−1, respectively. The apparent quantum efficiency of MoO3-x/ZIS for H2 evolution at 400 nm was about 13.92 %, which was 8.09 times higher than that of ZIS. Moreover, the MoO3-x/ZIS also displayed excellent activities on the selective 5-hydroxymethylfurfural dehydrogenation. The in-situ X-ray photoelectron spectroscopy, electron paramagnetic resonance, in-situ selective photodeposition, and density functional theory calculation confirmed the S-scheme charge transfer pathway between MoO3-x and ZIS. This study provides an effective avenue for designing multifunctional photocatalysts based on the synergistic effects of chemically bonded S-scheme heterostructure and nonmetallic LSPR effect.

Synergy of Ag and Interfacial Oxygen Vacancies on TiO2 for Highly Efficient Photocatalytic Production of H2O2.

Photocatalytic H2O2 production stands as a promising sustainable technology for chemical synthesis. However, rapid charge recombination and limited oxygen adsorption by photocatalysts often limit its efficiency. Herein, we demonstrate that the synergy of Ag and interfacial oxygen vacancies on TiO2 could overcome these challenges. The optimized Ag/TiO2-50 photocatalyst achieved an impressive H2O2 production rate of 12.9 mmol h-1 g-1 and maintained a steady-state concentration of 12.8 mM, significantly outperforming most TiO2-based photocatalysts documented in the literature. Detailed mechanistic studies, aided by TAS, in situ X-ray photoelectron spectroscopy (XPS), and in situ electron paramagnetic resonance (EPR) techniques, indicate that the oxygen vacancies at the Ag-TiO2 interface act as an interfacial hole trap, inducing a directional hole transfer. This, coupled with Ag acting as an electron acceptor, synergistically boosts the electron-hole separation. Additionally, the increased amount of oxygen vacancies at the Ag-TiO2 interface of Ag/TiO2-50 leads to enhanced O2 adsorption, thus contributing to its superior catalytic performance. This study provides valuable insights into interfacial traps in the charge transfer process and highlights the potential of interface regulation for achieving efficient photocatalytic conversion.

Scalable Layer-Controlled Oxidation of Bi2O2Se for Self-Rectifying Memristor Arrays With sub-pA Sneak Currents.

Smart memristors with innovative properties are crucial for the advancement of next-generation information storage and bioinspired neuromorphic computing. However, the presence of significant sneak currents in large-scale memristor arrays results in operational errors and heat accumulation, hindering their practical utility. This study successfully synthesizes a quasi-free-standing Bi2O2Se single-crystalline film and achieves layer-controlled oxidation by developing large-scale UV-assisted intercalative oxidation, resulting β-Bi2SeO5/Bi2O2Se heterostructures. The resulting β-Bi2SeO5/Bi2O2Se memristor demonstrates remarkable self-rectifying resistive switching performance (over 105 for ON/OFF and rectification ratios, as well as nonlinearity) in both nanoscale (through conductive atomic force microscopy) and microscale (through memristor array) regimes. Furthermore, the potential for scalable production of self-rectifying β-Bi2SeO5/Bi2O2Se memristor, achieving sub-pA sneak currents to minimize cross-talk effects in high-density memristor arrays is demonstrated. The memristors also exhibit ultrafast resistive switching (sub-100ns) and low power consumption (1.2 pJ) as characterized by pulse-mode testing. The findings suggest a synergetic effect of interfacial Schottky barriers and oxygen vacancy migration as the self-rectifying switching mechanism, elucidated through controllable β-Bi2SeO5 thickness modulation and theoretical ab initio calculations.

Crystal facet-modulated CuO/CeO2 catalysts for highly selective catalytic reduction of NO by CO

The selective catalytic reduction of NO by CO (CO-SCR) has a significant impact on the sustainable development of the environment. It is crucial to design efficient low-temperature catalysts to overcome the challenges associated with the industrialization of CO-SCR. Herein, we present CuO/CeO2 catalysts with three different exposed crystal facets of CeO2 ((100), (110), and (111)) synthesized by a hydrothermal method followed by impregnation for CO-SCR. Among the three CuO/CeO2 catalysts, CuO loaded on rod-like CeO2 catalyst (CuO/CeO2-R) with exposed CeO2 (110) crystal facet showed the highest catalytic performance in the CO-SCR reaction, achieving complete conversion of NO and 99 % conversion of CO at 250 °C. A series of characterizations reveal that the interaction between CuO and CeO2 with different crystal facets is crucial to regulating the interface structure and oxygen vacancy (Ov) content. During in situ DRIFTS analysis, it was found that the primary adsorption sites for CO are the Cu+-Ov-Ce3+ interface sites. The CuO/CeO2-R catalyst had the highest number of these sites. Furthermore, CuO/CeO2-R contained many Ov sites, which promote NO dissociation and enhance its catalytic efficiency. This study offers insights into CO-SCR catalysis and the design of efficient catalysts by manipulating the exposed crystal facets of support to enhance CO-SCR activity.

Strong metal-support interaction facilitated the formation of ternary alloy and interfacial oxygen vacancies for enhanced overall water splitting

The NiCoFe-based alloys are potential high-performing bifunctional electrocatalysts towards overall alkaline water splitting, though it is still challenging to achieve this goal. Herein, the NiCoFe/CeO2-x heterostructure with abundant interfacial oxygen vacancies is constructed through in-situ hydrogenation. The strong metal-support interaction favors the formation of the medium-entropy NiCoFe ternary alloy and the interfacial oxygen vacancies, while the introduction of the cobalt highly increases the electrochemically active surface area (ECSA). The ECSA of the NiCoFe/CeO2-x is more than 3 times those of the NiCoFe, NiFe/CeO2-x, NiCo/CeO2-x and CoFe/CeO2-x. Therefore, the NiCoFe/CeO2-x shows high catalytic performance towards both hydrogen evolution reaction and oxygen evolution reaction with a small overpotential of 42 and 238 mV at 10 mA cm−2 in 1 M KOH, respectively. More importantly, the NiCoFe/CeO2-x heterostructure with optimal elemental composition demonstrates excellent catalytic performance towards overall water splitting, exhibiting a small cell voltage of 1.52 V at 10 mA cm−2 without iR compensation. In addition, it shows good working stability in the overall water splitting at 100 mA cm−2 during a period of >10 h.

High-Performance TiO2 Thin-Film Transistors: In-Depth Investigation of the Correlation between Interface Traps and Oxygen Vacancies

High-Performance TiO₂ Thin-Film Transistors: In-Depth Investigation of the Correlation between Interface Traps and Oxygen Vacancies

Effects of polar discontinuities and stacking sequences on ferromagnetic properties at La0.67Sr0.33MnO3/SrCuO2 interfaces

Polar discontinuities occur in oxide heterostructures due to varying net charges in the sub-unit cell layers. These polar discontinuities lead to structural reconstruction and often create diverse functionalities. This work constructs polar discontinuous in La0.67Sr0.33MnO3/SrCuO2 (LSMO/SCO) heterostructures on a (001)-orientated SrTiO3 (STO) substrate under different configurations. By changing the growth order of LSMO and SCO, we found two different compensating mechanisms for polar discontinuity. When LSMO is grown on SCO, interfacial polarity discontinuities result in the generation of a large number of oxygen vacancies within the LSMO film. Thus, the LSMO magnetism deteriorates. For the SCO/LSMO/SCO trilayer, the SCO capping layer can recover the LSMO magnetism. The scanning transmission electron microscope results show an atomic reconstruction at the SCO-on-LSMO interface and several oxygen vacancies at the SrO sublayer. The interface reconfiguration releases the polar energy, thereby inhibiting the generation of oxygen vacancies and improving the ferromagnetism of the LSMO film. Our work studies the impact of polar discontinuity at the interface, providing insights into the effects of interface polar discontinuities on functional materials.

Interfacial oxygen vacancy engineering of double Z-scheme heterojunction Bi2MoO6/MnWO4/g-C3N4 for efficient photocatalytic degradation of iodohydrin

The synthesis of a dual Z-scheme heterojunction, Bi2MoO6/MnWO4/g-C3N4 (BMCM-x), enriched with oxygen voids, has been synthesized by an in-situ generation method. The ideal composite specimen, BMCM-50, managed to break down over 85 % of Iohexol in a span of 40 min. The emergence of oxygen voids serves to inhibit the merging of photogenerated carriers and fosters the creation of reactive radicals. The dual Z-scheme heterojunction is capable of isolating photogenerated carriers and enhancing redox capacity, markedly boosting BMCM-50’s photocatalytic breakdown efficiency.

Efficient Ozone Elimination Over MnO2 via Double Moisture-Resistance Protection of Active Carbon and CeO2.

The widespread ozone (O3) pollution is extremely hazardous to human health and ecosystems. Catalytic decomposition into O2 is the most promising method to eliminate ambient O3, while the fast deactivation of catalysts under humid conditions remains the primary challenge for their application. Herein, we elaborately developed a splendidly active and stable Mn-based catalyst with double hydrophobic protection of active carbon (AC) and CeO2 (CeMn@AC), which possessed abundant interfacial oxygen vacancies and excellent desorption of peroxide intermediates (O22-). Under extremely humid (RH = 90%) conditions and a high space velocity of 1200 L h-1 g-1, the optimized CeMn@AC achieved nearly 100% O3 conversion (140 h) at 5 ppm, showing unprecedented catalytic activity and moisture resistance toward O3 decomposition. In situ DRIFTS and theory calculations confirmed that the exceptional moisture resistance of CeMn@AC was ascribed to the double protection effect of AC and CeO2, which cooperatively prevented the competitive adsorption of H2O molecules and their accumulation on the active sites of MnO2. AC provided a hydrophobic reaction environment, and CeO2 further alleviated moisture deterioration of the MnO2 particles exposed on the catalyst surface via the moisture-resistant oxygen vacancies of MnO2-CeO2 crystal boundaries. This work offers a simple and efficient strategy for designing moisture-resistant materials and facilitates the practical application of the O3 decomposition catalysts in various environments.

Bimetallic oxide electrocatalyst with interfacial structure for enhanced electrocatalytic CO2 reduction

The development of electrochemical carbon dioxide reduction reaction (eCO2RR) electrocatalysts with high selectivity, high activity, low cost and high enrichment is an important research direction. We report a bimetallic oxide (CuO-Sb2O3) nanocomposite catalyst with interfacial structure formed by modifying CuO with Sb2O3 to enhance CO2 reduction. The CO faraday efficiency (FE) of CuO-Sb2O3 reaches 96.2 % in a CO2-saturated KHCO3 electrolyte at −1.05 V vs. RHE, which is better than that of pure CuO (28.2 %) and pure Sb2O3 (0 %, hydrogen only). In addition, CuO-Sb2O3 with an interfacial structure presents good stability. The increased activity of eCO2RR in producing CO is due to the unique surface and interfacial structure to capture CO2, and interfacial distortions and oxygen vacancies in its internal CuO and Sb2O3, which can provide more active centers and larger electrochemical active surface area (ECSA) to provide electron transfer and promote the formation of CO products. Besides, the interfacial effect for strong adsorption of *COOH and desorption of *CO improves the selectivity of CO.

Nickel Nanoparticles Supported on Lanthanum Oxycarbonate with Interfacial Oxygen Vacancies as Catalysts for CO2 Hydrogenation to Methane

Nickel Nanoparticles Supported on Lanthanum Oxycarbonate with Interfacial Oxygen Vacancies as Catalysts for CO₂ Hydrogenation to Methane

Enhanced the dehydrocyclization of 1,4-butanediol to γ-butyrolactone via the regulation of interface oxygen vacancies in Cu/MgO-CeO2 catalyst

Gas-phase dehydrocyclization of biomass-derived 1,4-butanediol (BDO) to γ-butyrolactone (GBL) is a sustainable and environmentally friendly process conducted at atmospheric pressure. In the present work, a series of 15Cu/xMgO-yCeO2 catalysts with different MgO: CeO2 ratios were prepared by the ammonia vaporization method. The gas-phase dehydrocyclization of BDO to GBL was carried out over these Cu-based catalysts synthesized in a fixed-bed reactor. The physicochemical properties of the catalysts were investigated by XRD, SEM, TEM, FTIR, N2 isothermal adsorption–desorption, H2-TPR, CO2-TPD, Raman, XPS, and EPR. The results indicated that the 15Cu/10MgO-90CeO2 catalyst exhibited a smaller particle size, higher specific surface area, and increased oxygen vacancies than the 15Cu/CeO2 catalyst. Operating conditions of 240 °C reaction temperature, 2.4 mL/h space velocity, and 98.92 % GBL yield from BDO dehydrogenation were achieved under 40 mL/min N2 flow for 4 h. Density functional theory (DFT) calculations confirmed that the 15Cu/10MgO-90CeO2 catalyst with more oxygen vacancies was more favorable for the adsorption and activation of BDO on the catalyst surface than 15Cu/CeO2, and its higher catalytic activity was attributed to the synergistic interaction between Cu+ and oxygen vacancies on the catalyst surface.

Interfacial oxygen vacancy engineering and built-in electric field mediated Z-scheme In2O3/Ag3PO4 heterojunction for boosted photocatalytic doxycycline degradation

Doxycycline pollutants in environment seriously destroy the balance of ecological system. A Z-scheme In2O3/Ag3PO4 heterojunction is constructed by attaching Ag3PO4 nanoparticles on hollow In2O3 hexagonal prism structures for efficient degradation of doxycycline. The doxycycline (30 mg/L) removal rate by IAO-1 (mole ratio of In2O3:Ag3PO4 is 1:3, 1.0 g/L) reaches 99.7% under visible light irradiation. Degradation rates are almost unchanged after five cycles of degradation experiments, demonstrating the excellent reusability and stability of the IAO-1 photocatalyst. The photocatalytic degradation of doxycycline in different water matrices by IAO-1 shows excellent performance, which provides significant potential for practical applications. The experiments and DFT results demonstrate that the built-in electric fields in IAO-1 contribute to the charge transfer from Ag3PO4 to In2O3, leading to the formation of a Z-scheme heterojunction with high redox capacity. The hollow defect structure of IAO-1 effectively activates molecular oxygen to generate oxygen vacancies and induce 1O2 production through energy transfer, which promotes the attack of benzene rings and oxygen-containing groups in the molecular structure of doxycycline, leading to hydroxylation, demethylation, and ring-opening reactions. This work provides new ideas for constructing Z-scheme photocatalysts with oxygen vacancies and built-in electric fields for practical wastewater treatment.

Tuning interfacial oxygen vacancy level of bismuth oxybromide to enhance photocatalytic degradation of bisphenol A

Oxygen vacancies (OVs) have garnered significant interest for their role as active sites, enhancing the catalytic efficiency of various catalysts. Despite their widespread application in environmental purification processes, the generation of OVs conventionally depends on high-temperature conditions and strong reducing agents for the extraction of surface partial oxygen atoms from catalysts. In this work, bismuth oxybromide (BiOBr) nanosheets with varying levels of OVs were synthesized via a simple and effective solvothermal method. This novel method affords precise control over the conduction band (CB) and valence band (VB) positions of BiOBr. The presence of different OVs exhibited varying photocatalytic efficiencies in the degradation of bisphenol A (BPA) under visible light irradiation, with higher levels of OVs resulting in superior photocatalytic performance. Furthermore, radical scavenger experiments demonstrated that superoxide oxides (O2•−) and holes (h+) were the primary reactive oxygen species for BPA degradation. Additionally, BiOBr-OVs exhibited excellent anti-interference and stability in water matrices containing diverse inorganic anions and organic compounds. This work provides a simple and effective approach for the fine-regulating of catalysts through interfacial defect engineering, paving the way for their practical application in environmental decontamination.

Spatial interfacial heterojunctions of TiO2 for photocatalytic degradation of toluene: Effects of interface amorphous region and oxygen vacancy

The catalytic activity of TiO2 is contingent upon its crystal structure and the optoelectronic properties associated with defects. In this study, a one-step method was used to synthesize TiO2 with a spatial interface of rutile/anatase phases, and a simple thermal annealing process was applied to optimize the amorphous regions and oxygen vacancies at the interface between the rutile and anatase phases of TiO2. High-resolution transmission electron microscopy (HRTEM) elucidates the evolution process of the amorphous domain at the interface, skillfully introducing oxygen vacancies at the heterojunction interface by modulating the amorphous domain. The obtained photocatalyst (TiO2–350 °C) after annealing exhibits an optimal interface structure, with its photocatalytic activity and stability in degrading toluene far superior to P25. Photocurrent and photoluminescence (PL) measurements affirm that the existence of interfacial oxygen vacancies heightens the efficiency of electron transfer at the interface, while surface oxygen vacancies significantly enhance the stability and mineralization rate of toluene degradation. The improved photocatalytic properties were attributed to the combined effects of surface/interface oxygen vacancies and spatial interface heterojunctions. The one-step synthesis method developed in this work provides a novel perspective on combining spatially interfaced anatase/rutile phases with surface/interfacial oxygen vacancies.

Oxygen Vacancy and Heterostructure Modulation of Co2P/Fe2P Electrocatalysts for Improving Total Water Splitting.

Designing a stable and highly active catalyst for hydrogen evolution and oxygen evolution reactions (HER/OER) is essential for the industrialization of hydrogen energy but remains a major challenge. This work reports a simple approach to fabricating coupled Co2P/Fe2P nanorod array catalyst for overall water decomposition, demonstrating the source of excellent activity in the catalytic process. Under alkaline conditions, Co2P/Fe2P heterostructures exhibit an overpotential of 96 and 220 mV for HER and OER, respectively, at 10 mA cm-2. For total water splitting, a low voltage of 1.56 V is required to provide a current density of 10 mA cm-2. And the catalyst exhibits long-term durability for 30 h at a high current density of 250 mA cm-2. The analysis of the results revealed that the presence of interfacial oxygen vacancies and the strong interaction between Co2P/Fe2P provided the catalyst with more electrochemically active sites and a faster charge transfer capability, which improved the hydrolysis dissociation process. Electrochemically active metal (oxygen) hydroxide phases were produced after OER stability testing. The results of this study prove its great potential in practical industrial electrolysis and provide a reasonable and feasible strategy for the design of nonprecious metal phosphide electrocatalysts.

Metastabilizing the Ruthenium Clusters by Interfacial Oxygen Vacancies for Boosted Water Splitting Electrocatalysis

AbstractMetal–support interaction (MSI) is witnessed as an essential manner to stabilize active metals and tune catalytic activity for heterogonous water splitting. Kinetically driving the water electrolysis (WE) appeals for a rational MSI system with the coupled electron‐donating/accepting (e‐D/A) characters for hydrogen/oxygen evolution reactions (HER/OER). However, the metal stabilization effect by MSI will in turn restrict the deblocking of e‐D/A properties and challenge the full electrocatalytic optimization. This study profiles a heterostructure featuring metastable Ru clusters on defective NiFe hydroxide (Ru/d‐NiFe LDH) support as a low‐precious (≈2 wt%) catalytic platform for efficient WE. It is indicated that the interfacial oxygen vacancies can deviate the stable Ru 4d5 orbit to a metastable Ru2+δ state, and regulate the metal d‐band center levels toward the facilitated HER/OER processes. Resultantly, the Ru/d‐NiFe LDH heterostructure attains the ultralow overpotentials at 10 mA cm−2 for Pt‐beyond alkaline HER (18 mV) and OER (220 mV) with fast kinetics and durability. The symmetrical water electrolyzer delivers a promising voltage of 1.49 V at 10 mA cm−2 in 1 m KOH and efficient seawater splitting performance. This work carries interesting opportunities in rationalizing sophisticated metal‐support electrocatalysts through metal‐site metastabilization engineering.

Insight into the extremely different catalytic behaviors of asymmetric and symmetric oxygen vacancies for peroxymonosulfate activation

Oxygen vacancies (OVs) play crucial role in peroxymonosulfate (PMS) activation, however, the corresponding catalytic mechanism is ambiguous. Herein, we constructed abundant interfacial asymmetric oxygen vacancies (As-OVs) in OVs-ZnO/Co3O4 that displayed remarkable different catalytic behavior from the symmetric oxygen vacancies (S-OVs) in OVs-CoOx. Specifically, the As-OVs achieved ultra-fast contaminants degradation (∼ 1 min) through both radical attack and electron-transfer process (ETP), while S-OVs exhibited sluggish kinetics for both pathways. Experimental and theoretical analyses revealed that PMS was easily adsorbed on the As-OVs to form PMS* , then ETP immediately occurred once OVs-ZnO/Co3O4 encountered with electron-rich bisphenol A. When electron-poor benzoic acid replaced bisphenol A, the peroxide bond was quickly broken to produce radicals due to the largely polarized PMS* on the asymmetric sites. Conversely, the S-OVs cannot realize rapid removal of both targets because the symmetric sites weakened ETP. This work provides atomic-level insights to understand the catalytic behaviors of OVs.

Effects of oxygen vacancies and interfacial strain on the metal-insulator transition of VO2 nanobeams.

The role of oxygen vacancies and interfacial strain on the metal-insulator transition (MIT) behavior of high-quality VO2 nanobeams (NBs) synthesized on SiO2/Si substrates employing V2O5 as a precursor has been investigated in this research. Selective oxygen vacancies have been generated by argon plasma irradiation. The MIT is progressively suppressed as the duration of plasma processing increases; in addition, the temperature of MIT (TMIT) drops by up to 95 K relative to the pristine VO2 NBs. Incorporating oxygen vacancies into VO2 may increase its electron concentration, which might shift the Fermi levels upward, strengthen the electronic orbital overlap of the V-V chains, and further stabilize the metallic phase at lower temperatures, based on first-principles calculations. Furthermore, in order to evaluate the influence of substrate-induced strain in our situation, the MIT in two distinct types of VO2 NB samples is examined without metal contacts by using the distinctive light scattering characteristics of the metal (M) and insulator (I) phases (i.e., M/I domains) by optical microscopy. It is found that the domain structures in the "clamped" NBs persisted up to ∼453 K, while the "released" NBs (transferred to a new substrate) did not exhibit any domain structures and turned into an entirely M phase with a dark contrast above ∼348 K. When combined with first-principles calculations, the electronic orbital occupancy in the rutile phase contributes to explaining the interfacial strain-induced modulation of MIT. The current findings shed light on how interfacial strain and oxygen vacancies impact MIT behavior. It also suggests several types of control strategies for MIT in VO2 NBs, which are essential for a broader spectrum of VO2 NB applications.