Collective Control of Potential-Constrained Oxygen Vacancies in Oxide Heterostructures for Gradual Resistive Switching

Filamentary resistive switching in oxides is one of the key strategies for developing next-generation non-volatile memory devices. However, despite numerous advantages, their practical applications in neuromorphic computing are still limited due to non-uniform and indeterministic switching behavior. Given the inherent stochasticity of point defect migration, the pursuit of reliable switching likely demands an innovative approach. Herein, a collective control of oxygen vacancies is introduced in LaAlO₃/SrTiO₃ (LAO/STO) heterostructures to achieve reliable and gradual resistive switching. By exploiting an electrostatic potential constraint in ultrathin LAO/STO heterostructures, the formation of conducting filaments is suppressed, but instead precisely control the concentration of oxygen vacancies. Since the conductance of the LAO/STO device is governed by the ensemble concentration of oxygen vacancies, not their individual probabilistic migrations, the resistive switching is more uniform and deterministic compared to conventional filamentary devices. It provides direct evidence for the collective control of oxygen vacancies by spectral noise analysis and modeling by Monte-Carlo simulation. As a proof of concept, the significantly-improved analog switching performance of the filament-free LAO/STO devices is demonstrated, revealing potential for neuromorphic applications. The results establish an approach to store information by point defect concentration, akin to biological ionic channels, for enhancing switching characteristics of oxide materials.     

Achieving Long-Enduring High-Voltage Oxygen Redox in P2-Structured Layered Oxide Cathodes by Eliminating Nonlattice Oxygen Redox

Triggering reversible lattice oxygen redox (LOR) in oxide cathodes is a paradigmatic approach to overcome the capacity ceiling determined by orthodox transition-metal (TM) redox. However, the LOR reactions in P2-structured Na-layered oxides are commonly accompanied by irreversible nonlattice oxygen redox (non-LOR) and large local structural rearrangements, bringing about capacity/voltage fading and constantly evolving charge/discharge voltage curves. Herein, a novel Na_0.615Mg_0.154Ti_0.154Mn_0.615◻_0.077O₂ (◻ = TM vacancies) cathode with both Na O Mg and Na O ◻ local configurations is deliberately designed. Intriguingly, the activating of oxygen redox at middle-voltage region (2.5–4.1 V) via Na O ◻ configuration helps in maintaining the high-voltage plateau from LOR (≈4.38 V) and stable charge/discharge voltage curves even after 100 cycles. Hard X-ray absorption spectroscopy (hXAS), solid-state NMR, and electron paramagnetic resonance studies demonstrate that both the involvement of non-LOR at high-voltage and the structural distortions originating from Jahn–Teller distorted Mn³⁺O₆ at low-voltage are effectively restrained in Na_0.615Mg_0.154Ti_0.154Mn_0.615◻_0.077O₂. Resultantly, the P2 phase is well retained in a wide electrochemical window of 1.5–4.5 V (vs Na⁺/Na), resulting in an extraordinary capacity retention of 95.2% after 100 cycles. This work defines an effective approach to upgrade the lifespan of Na-ion battery with reversible high-voltage capacity provided by LOR.     

Engineering Oxygen Vacancies in a Polysulfide-Blocking Layer with Enhanced Catalytic Ability

The practical application of the lithium–sulfur (Li–S) battery is seriously restricted by its shuttle effect, low conductivity, and low sulfur loading. Herein, first-principles calculations are conducted to verify that the introduction of oxygen vacancies in TiO₂ not only enhances polysulfide adsorption but also greatly improves the catalytic ability and both the ion and electron conductivities. A commercial polypropylene (PP) separator decorated with TiO₂ nanosheets with oxygen vacancies (OVs-TiO₂@PP) is fabricated as a strong polysulfide barrier for the Li–S battery. The thickness of the OVs-TiO₂ modification layer is only 500 nm with a low areal mass of around 0.12 mg cm⁻², which enhances the fast lithium-ion penetration and the high energy density of the whole cell. As a result, the cell with the OVs-TiO₂@PP separator exhibits a stable electrochemical behavior at 2.0 C over 500 cycles, even under a high sulfur loading of 7.1 mg cm⁻², and an areal capacity of 5.83 mAh cm⁻² remains after 100 cycles. The proposed strategy of engineering oxygen vacancies is expected to have wide applications in Li–S batteries.     

Rationalizing the Effect of Oxygen Vacancy on Oxygen Electrocatalysis in Li–O2 Battery

Albeit the effectiveness of surface oxygen vacancy in improving oxygen redox reactions in Li–O₂ battery, the underpinning reason behind this improvement remains ambiguous. Herein, the concentration of oxygen vacancy in spinel NiCo₂O₄ is first regulated via magnetron sputtering and its relationship with catalytic activity is comprehensively studied in Li–O₂ battery based on experiment and density functional theory (DFT) calculation. The positive effect posed by oxygen vacancy originates from the up shifted antibond orbital relative to Fermi level (E_f), which provides extra electronic state around E_f, eventually enhancing oxygen adsorption and charge transfer during oxygen redox reactions. However, with excessive oxygen vacancy, the negative effect emerges because the metal ions are mostly reduced to low valence based on the electrical neutral principle, which not only destabilizes the crystal structure but also weakens the ability to capture electrons from the antibond orbit of Li₂O₂, leading to poor catalytic activity for oxygen evolution reaction (OER).     

Formation Energy Profiles of Oxygen Vacancies at Grain Boundaries in Perovskite-Type Electroceramics

Oxygen vacancy formation energies play a major role in the electric field-assisted abnormal grain growth of technologically relevant polycrystalline perovskite phases. The underlying effect on the atomic scale is assumed to be a redistribution of cationic and anionic point defects between grain boundaries (GBs) and the bulk interior regions of the grains due to different defect formation energies in the structurally different regions, accompanied by the formation of space charge zones. Using atomistic calculations based on classical interatomic potentials, optimized structures of the symmetric tilt GBs Σ5(210)[001] and Σ5(310)[001], and of the asymmetric tilt GB (430)[001]||(100)[001] in the electroceramic perovskite materials SrTiO₃, BaTiO₃, and BaZrO₃, are derived and discussed. Profiles of oxygen vacancy formation energies across those GBs are presented and their dependence on composition and GB type is discussed.     

Defect-Induced Atomic Arrangement in CoFe Bimetallic Heterostructures with Boosted Oxygen Evolution Activity

Three CoFe-bimetallic oxides with different compositions (termed as CoFeO_x-A/N/H) are prepared by thermally treating metal-organic-framework (MOF) precursors under different atmospheres (air, N_2, and NaBH₄/N₂), respectively. With the aid of vast oxygen vacancies (O_v), cobalt at tetrahedral sites (Co²⁺(Th)) in spinel Co₃O₄ is diffused into interstitial octahedral sites (Oh) to form rocksalt CoO and ternary oxide CoFe₂O₄ has been induced to give the unique defective CoO/CoFe₂O₄ heterostructure. The resultant CoFeO_x-H exhibits superb electrocatalytic activity toward water oxidation: overpotential at 10 mA cm⁻² is 192 mV, which is 122 mV smaller than that of CoFeO_x-A. The smaller Tafel slope (42.53 mV dec⁻¹) and higher turnover frequency (785.5 h⁻¹) suggest fast reaction kinetics. X-ray absorption spectroscopy, ex situ characterizations, and theoretical calculations reveal that defect engineering effectively tunes the electronic configuration to a more active state, resulting in the greatly decreased binding energy of oxo intermediates, and consequently much lower catalytic overpotential. Moreover, the construction of hetero-interface in CoFeO_x-H can provide rich active sites and promote efficient electron transfer. This work may shed light on a comprehensive understanding of the modulation of electron configuration of bimetallic oxides and inspire the smart design of high-performance electrocatalysts.     

An Unusual Strong Visible‐Light Absorption Band in Red Anatase TiO2 Photocatalyst Induced by Atomic Hydrogen‐Occupied Oxygen Vacancies

Increasing visible light absorption of classic wide‐bandgap photocatalysts like TiO₂ has long been pursued in order to promote solar energy conversion. Modulating the composition and/or stoichiometry of these photocatalysts is essential to narrow their bandgap for a strong visible‐light absorption band. However, the bands obtained so far normally suffer from a low absorbance and/or narrow range. Herein, in contrast to the common tail‐like absorption band in hydrogen‐free oxygen‐deficient TiO₂, an unusual strong absorption band spanning the full spectrum of visible light is achieved in anatase TiO₂ by intentionally introducing atomic hydrogen‐mediated oxygen vacancies. Combining experimental characterizations with theoretical calculations reveals the excitation of a new subvalence band associated with atomic hydrogen filled oxygen vacancies as the origin of such band, which subsequently leads to active photo‐electrochemical water oxidation under visible light. These findings could provide a powerful way of tailoring wide‐bandgap semiconductors to fully capture solar light.     

In Situ Formation of Oxygen Vacancies Achieving Near-Complete Charge Separation in Planar BiVO4 Photoanodes

Despite a suitable bandgap of bismuth vanadate (BiVO₄) for visible light absorption, most of the photogenerated holes in BiVO₄ photoanodes are vanished before reaching the surfaces for oxygen evolution reaction due to the poor charge separation efficiency in the bulk. Herein, a new sulfur oxidation strategy is developed to prepare planar BiVO₄ photoanodes with in situ formed oxygen vacancies, which increases the majority charge carrier density and photovoltage, leading to a record charge separation efficiency of 98.2% among the reported BiVO₄ photoanodes. Upon loading NiFeO_x as an oxygen evolution cocatalyst, a stable photocurrent density of 5.54 mA cm⁻² is achieved at 1.23 V versus the reversible hydrogen electrode (RHE) under AM 1.5 G illumination. Remarkably, a dual-photoanode configuration further enhances the photocurrent density up to 6.24 mA cm⁻², achieving an excellent applied bias photon-to-current efficiency of 2.76%. This work demonstrates a simple thermal treatment approach to generate oxygen vacancies for the design of efficient planar photoanodes for solar hydrogen production.     

Chemical Strain Engineering of Magnetism in Oxide Thin Films

Transition metal oxides having a perovskite structure form a wide and technologically important class of compounds. In these systems, ferroelectric, ferromagnetic, ferroelastic, or even orbital and charge orderings can develop and eventually coexist. These orderings can be tuned by external electric, magnetic, or stress field, and the cross‐couplings between them enable important multifunctional properties, such as piezoelectricity, magneto‐electricity, or magneto‐elasticity. Recently, it has been proposed that additional to typical fields, the chemical potential that controls the concentration of ion vacancies in these systems may reveal an efficient alternative parameter to further tune their properties and achieve new functionalities. In this study, concretizing this proposal, the authors show that the control of the content of oxygen vacancies in perovskite thin films can indeed be used to tune their magnetic properties. Growing PrVO₃ thin films epitaxially on an SrTiO₃ substrate, the authors reveal a concrete pathway to achieve this effect. The authors demonstrate that monitoring the concentration of oxygen vacancies through the oxygen partial pressure or the growth temperature can produce a substantial macroscopic tensile strain of a few percent. In turn, this strain affects the exchange interactions, producing a nontrivial evolution of Néel temperature in a range of 30 K.     

Quantum Conductance Probing of Oxygen Vacancies in SrTiO3 Epitaxial Thin Film using Graphene

Quantum Hall conductance in monolayer graphene on an epitaxial SrTiO₃ (STO) thin film is studied to understand the role of oxygen vacancies in determining the dielectric properties of STO. As the gate‐voltage sweep range is gradually increased in the device, systematic generation and annihilation of oxygen vacancies, evidenced from the hysteretic conductance behavior in the graphene, are observed. Furthermore, based on the experimentally observed linear scaling relation between the effective capacitance and the voltage sweep range, a simple model is constructed to manifest the relationship among the dielectric properties of STO with oxygen vacancies. The inherent quantum Hall conductance in graphene can be considered as a sensitive, robust, and noninvasive probe for understanding the electronic and ionic phenomena in complex transition‐metal oxides without impairing the oxide layer underneath.     

Tuning Oxygen Vacancies in Ultrathin TiO2 Nanosheets to Boost Photocatalytic Nitrogen Fixation up to 700 nm

Dinitrogen reduction to ammonia using transition metal catalysts is central to both the chemical industry and the Earth's nitrogen cycle. In the Haber–Bosch process, a metallic iron catalyst and high temperatures (400 °C) and pressures (200 atm) are necessary to activate and cleave N?N bonds, motivating the search for alternative catalysts that can transform N₂ to NH₃ under far milder reaction conditions. Here, the successful hydrothermal synthesis of ultrathin TiO₂ nanosheets with an abundance of oxygen vacancies and intrinsic compressive strain, achieved through a facile copper‐doping strategy, is reported. These defect‐rich ultrathin anatase nanosheets exhibit remarkable and stable performance for photocatalytic reduction of N₂ to NH₃ in water, exhibiting photoactivity up to 700 nm. The oxygen vacancies and strain effect allow strong chemisorption and activation of molecular N₂ and water, resulting in unusually high rates of NH₃ evolution under visible‐light irradiation. Therefore, this study offers a promising and sustainable route for the fixation of atmospheric N₂ using solar energy.     

Engineering of Electronic States on Co3O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction

Due to the earth abundance and tunable electronic properties, etc., transition metal oxides (TMOs) show attractive attention in oxygen evolution reaction. O‐vacancies (V_o) play important roles in tailoring the local surface and electronic environment to lower the activation barriers. Herein, an effective strategy is shown to enhance the oxygen evolution reduction (OER) performance on Co₃O₄ ultrathin nanosheets via combined cation substitution and anion vacancies. The oxygen‐deficient Fe‐Co‐O nanosheets (3–4 nm thickness) display an overpotential of 260 mV@10 mA cm^?2 and a Tafel slope of 53 mV dec^?1, outperforming those of the benchmark RuO₂ in 1.0 m KOH. Further calculations demonstrate that the combined introduction of Fe cation and V_o with appropriate location and content finely tune the intermediate absorption, consequently lowering the rate‐limiting activation energy from 0.82 to as low as 0.15 eV. The feasibility is also proved by oxygen‐deficient Ni‐Co‐O nanosheets. This work not only establishes a clear atomic‐level correlation between cation substitution, anion vacancies, and OER performance, but also provides valuable insights for the rational design of highly efficient catalysts for OER.     

紫外分光光度法测定水中化学需氧量的不确定度评定

依据HJ/T 399-2007,选取含量接近法规限值的代表性样品,从基准物质溯源,探索测定水中化学需氧量的数学模型,对检测过程中引入的不确定度进行了分类和量化,系统全面地评定了各个不确定度分量,得到该方法的相对标准不确定度为0.033。     

Tuning Surface Electronic Configuration of NiFe LDHs Nanosheets by Introducing Cation Vacancies (Fe or Ni) as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Intrinsically inferior electrocatalytic activity of NiFe layered double hydroxides (LDHs) nanosheets is considered as a limiting factor to inhibit the electrocatalytic properties for oxygen evolution reaction (OER). Proper defect engineering to tune the surface electronic configuration of electrocatalysts may significantly improve the intrinsic activity. In this work, the selective formation of cation vacancies in NiFe LDHs nanosheets is successfully realized. The as‐synthesized NiFe LDHs‐V_Fe and NiFe LDHs‐V_Ni electrocatalysts show excellent activity for OER, mainly attributed to the introduction of rich iron or nickel vacancies in NiFe LDHs nanosheets, which efficiently tune the surface electronic structure increasing the adsorbing capacity of OER intermediates. Density functional theory (DFT) computational results also further indicate that the OER catalytic performance of NiFe LDHs can be pronouncedly improved by introducing Fe or Ni vacancies.     

硫酸溶液中铅系析氧阳极的应用研究

本文对铅及铅－锑合金在硫酸水溶液中作析氧阳极的氧化特点、腐蚀行为及极化特性进行了研究。结合硝基苯电解还原制对氨基苯酚这一过程，在这实验室小试及工厂中试的基础上，讨论了该类阳极加工，维护及操作等问题。     

Synergistic Effect of N-NiMoO4/Ni Heterogeneous Interface with Oxygen Vacancies in N-NiMoO4/Ni/CNTs for Superior Overall Water Splitting

The exploring of economical, high-efficiency, and stable bifunctional catalysts for hydrogen evolution and oxygen evolution reactions (HER/OER) is highly imperative for the development of electrolytic water. Herein, a 3D cross-linked carbon nanotube supported oxygen vacancy (V_o)-rich N-NiMoO₄/Ni heterostructure bifunctional water splitting catalyst (N-NiMoO₄/Ni/CNTs) is synthesized by hydrothermal-H₂ calcination method. Physical characterization confirms that V_o-rich N-NiMoO₄/Ni nanoparticles with an average size of ≈19 nm are secondary aggregated on CNTs that form a hierarchical porous structure. The formation of Ni and NiMoO₄ heterojunctions modify the electronic structure of N-NiMoO₄/Ni/CNTs. Benefiting from these properties, N-NiMoO₄/Ni/CNTs drives an impressive HER overpotential of only 46 mV and OER overpotential of 330 mV at 10 mA cm⁻², which also shows exceptional cycling stability, respectively. Furthermore, the as-assembled N-NiMoO₄/Ni/CNTs||N-NiMoO₄/Ni/CNTs electrolyzer reaches a cell voltage of 1.64 V at 10 mA cm⁻² in alkaline solution. Operando Raman analysis reveals that surface reconstruction is essential for the improved catalytic activity. Density functional theory (DFT) calculations further demonstrate that the enhanced HER/OER performance should be attributed to the synergistic effect of V_o and heteostructure that improve the conductivity of N-NiMoO₄/Ni/CNTs and facilitatethe desorption of reaction intermediates.