Non-catalytic hydrogenation of VO2 in acid solution

Compressive Strain-Induced Uphill Hydrogen Distribution in Strontium Ferrite Films

Hydrogen incorporation into metal oxides enhances their electrochemical properties, making them highly suitable for various energy conversion applications. The controlled distribution of hydrogen ions in material systems and their conduction at elevated temperatures have garnered significant attention for various energy storage and environmental monitoring applications, including fuel cells, smart windows, and sensor technologies. In this work, cost-effective, high-concentration hydrogen-doped SrFeO3-δ (HSrFeO3-δ) films were prepared under ambient conditions by treating Al(s)|SrFeO3-δ(s) films with KOH(aq), utilizing electron-proton codoping to investigate hydrogen distribution. The uphill hydrogen distributions in SrFeO3-δ films with compressive strain, in contrast to the density gradient behavior under tensile strain, suggest the fundamental role of the strain states in the hydrogen accommodation. Compressively strained films with a rich Al source follow an anomalous uphill feature of hydrogen distribution, highlighting their potential use as electrolyte for fuel cells. The strain significantly influences the structure, chemical lattice coupling, and consequently the ionic transport in SrFeO3-δ. Ionic conductivity measurements reveal that compressively strained HSrFeO3-δ films with uphill hydrogen distributions exhibit a significant ionic conductivity of 0.189 S/cm at 413 K, with an activation energy of approximately 0.29 eV, making them suitable for low-temperature electrochemical applications. These findings provide a promising approach for tuning material properties and valuable insights for building iontronic devices.

Hydrogen-Associated Filling-Controlled Mottronics Within Thermodynamically Metastable Vanadium Dioxide

The discovery of hydrogen-associated topotactic phase modulations in correlated oxide system has emerged as a promising paradigm to explore exotic electronic states and physical functionality. Here hydrogen-induced Mott phase transitions are demonstrated for metastable VO2 (B) toward new electron-itinerant hydrogenated phases via introducing non-equilibrium condition, delicately delivering a rich spectrum of hydrogen-associated electronic states. Of particular interest, the highly robust but reversible hydrogenated phase achievable in metastable VO2 (B) significantly benefits protonic device applications, which is in contrast with well-known VO2 (M1), where the metallic hydrogenated phase readily turns into insulating state with extensive hydrogen doping. Establishing correlated VO2 at metastable status fundamentally surpasses the thermodynamic restrictions to expand the adjustability in their electronic structure, giving rise to new electronic states and a superior resistive switching of 102-105 to the counterparts in widely-reported VO2 (M1). Utilizing the theoretical calculations and synchrotron radiation analysis, the hydrogen-associated phase modulation in metastable VO2 (B) is dominantly driven by band-filling-controlled orbital reconfiguration, while the concurrent structural evolution unveils a strong ion-electron-lattice coupling. The present work provides fundamentally new tuning knob for adjusting the energy landscape of electron-correlated system, advancing the rational design of unachievable electronic states in hydrogen-related equilibrium phase diagram.

Interfering with proton and electron transfer enables antibacterial starvation therapy

Implant-associated infections are urgently addressed; however, existing materials are difficult to kill bacteria without damaging cells. Here, we propose an innovative concept of selective antibacterial starvation therapy based on interfering with proton and electron transfer on the bacterial membrane. As a proof-of-principle demonstration, a special Schottky heterojunction film composed of gold and alkaline magnesium-iron mixed metal oxides (Au/MgFe-MMO) was constructed on the titanium implant. Once bacteria contacted this implant, the Au/MgFe-MMO film continuously captured the proton and electron participated in respiratory chain of bacteria to impede their energy metabolism, leading to the deficit of adenosine 5'-triphosphate. Prolonged exposure to this starvation state inhibited numerous biosynthesis processes and triggered severe oxidative stress in bacteria, ultimately leading to their death due to DNA and membrane damage. In addition, this heterojunction film was comfortable for mammalian cells, without inhibiting mitochondrial function. This proposed starvation antibacterial therapy gives a notable perspective in designing biosafe smart antibacterial biomaterials.

H Induced Metal-Insulation Transition Boosts the Stability of High Temperature Polymer Electrolyte Membrane Fuel Cells

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) have garnered significant attention due to their expanded range of hydrogen sources and simplified management systems. However, the frequent start-up and shut-down (SU/SD) caused fuel starvation operation condition seriously deteriorates the performance and lifetime of the fuel cell. In this manuscript, VO2 was incorporated in the anode to restrain fuel starvation of the electrode. Under the operation condition, the insulative VO2 would reversibly transform into metallic HxVO2 by intercalating hydrogen, and HxVO2 can automatically release hydrogen, which could act as the hydrogen buffer and suppress reverse-current degradation. After the hydrogen release, the generated insulating VO2 would prevent the side reactions during fuel starvation. Compared to the traditional Pt anode, the electrode with VO2 showed much higher output power and greatly improved durability after fuel starvation. This work demonstrates the in situ reversible hydrogen storage/release-controlled metal-insulator phase transition strategy to enhance the durability of fuel cells.

Quantitative Study of Reversible Nonvolatile VO2 Thin Films Through Plasma Driven Phase Engineering Process

The nanoscale control of phase transition in correlated materials offers significant insight into phase transition dynamics for the advancement of future nanoelectronics devices. This study explores the phase transition phenomenon in vanadium dioxide (VO2), focusing on the heterogeneous phases evolved after low-pressure plasma irradiation on VO2 thin films, a strong electron-correlated material. The modulation in the Argon (Ar) plasma power reveals the formation of homogeneous and heterogeneous phases with variable resistive states at room temperature. High-resolution transmission electron microscopy (HRTEM) is observed with the change in interplanar spacing revealing monoclinic (M1) at 0W, monoclinic-tetragonal rutile (phase coexistence, M1-R) at 50W, and tetragonal rutile (R) at 90W. Dielectric force microscopy (DFM) shows distinct dielectric responses corresponding to different phases, characterized by potential differences of 3 mV (M1), 5 mV (M1-R), and 7.44 mV (R) phases. The coexistence of M1-R phase is stabilized and examined at room temperature, with variations in the charge carrier density observed relative to M1 and R phases individually. The phase change in VO2 is found to be reversible, enabling stable resistive states even after the plasma is removed. The changes in plasma geometry help find and stabilize unstable phases, which can be useful in nanoelectronics.

Stabilization of oxygen vacancy ordering and electrochemical-proton-insertion-and-extraction-induced large resistance modulation in strontium iron cobalt oxides Sr(Fe,Co)Oy

Electrochemically inserting and extracting hydrogen into and from solids are promising ways to explore materials' phases and properties. However, it is still challenging to identify the structural factors that promote hydrogen insertion and extraction and to develop materials whose functional properties can be largely modulated by inserting and extracting hydrogen through solid-state reactions at room temperature. In this study, guided by theoretical calculations on the energies of oxygen reduction and hydrogen insertion reactions with oxygen-deficient perovskite oxides, we demonstrated that the oxygen vacancy ordering in Sr(Fe1-xCox)Oy (SFCO) epitaxial films can be stabilized by increasing the Co content (x ≥ 0.3) and revealed that it plays a key role in promoting proton accommodation into the SFCO lattice. We also show that the electrical resistance of SFCO films can be reversibly modulated by electrochemical proton insertion and extraction, and the modulation exceeds three orders of magnitude for Sr(Fe0.5Co0.5)O2.5 epitaxial films. Our results provide guidelines for controlling material properties through the insertion and extraction of hydrogen and for designing and exploring hydrogen-insertion materials.

Selective Laser Doping and Dedoping for Phase Engineering in Vanadium Dioxide Film

Vanadium dioxide (VO2), renowned for its reversible metal-to-insulator transition (MIT), has been widely used in configurable photonic and electronic devices. Precisely tailoring the MIT of VO2 on micro-/nano-scale is crucial for miniaturized and integrated devices. However, existing tailoring techniques like scanning probe microscopy, despite their precision, fall short in efficiency and adaptability, particularly on complex or curved surfaces. Herein, this work achieves the local engineering of the phase of VO2 films in high efficiency by employing laser writing to assist in the hydrogen doping or dedoping process. The laser doping and laser dedoping technique is also highly flexible, enabling the fabrication of reconfigurable, non-volatile, and multifunctional VO2 devices. This approach establishes a new paradigm for creating reconfigurable micro/nanophotonic and micro/nanoelectronic devices.

Galvanic hydrogenation reaction in metal oxide

Rational reforming of metal oxide has a potential importance to modulate their inherent properties toward appealing characteristics for various applications. Here, we present a detailed fundamental study of the proton migration phenomena between mediums and propose the methodology for controllable metal oxide hydrogenation through galvanic reactions with metallic cation under ambient atmosphere. As a proof of concept for hydrogenation, we study the role of proton adoption on the structural properties of molybdenum trioxide, as a representative, and its impact on redox characteristics in Li-ion battery (LiB) systems using electrochemical experiments and first-principles calculation. The proton adoption contributes to a lattice rearrangement facilitating the faster Li-ion diffusion along the selected layered and mediates the diffusion pathway that promote the enhancements of high-rate performance and cyclic stability. Our work provides physicochemical insights of hydrogenations and underscores the viable approach for improving the redox characteristics of layered oxide materials.

Sol-Gel Pt-VO2 Films as Selective Chemoresistive and Optical H2 Gas Sensors

In this work, VO2 (M1/R) thin films were exploited as H2 gas sensors. A flat film morphology, obtained by furnace annealing, was compared with a laser-induced nanostructured one. The combination of the environmentally friendly sol-gel approach with the ultrafast laser crystallization allows for significant reductions in energy consumption and related emissions during the fabrication of VO2 sensors. By decorating the sensors' surface with Pt nanoparticles (NPs), the sensor response was enhanced exploiting the hydrogen spillover effect. The Pt/VO2 sensors, tested at operating temperatures between 20 and 200 °C and for concentration of H2 from few ppm to 50000 ppm, offered a dual chemoresistive and optical sensing mode. Low operating temperatures of 150 °C were achieved, along with a detection limit as low as 2 ppm and a perfect baseline recovery. Both sensors guaranteed specific selectivity toward H2, without response to NO2 or humidity, and long-term stability over 500 h. The H2 sensing mechanism, for both the monoclinic and rutile VO2 phases, was investigated through in operando X-ray Diffraction and in situ X-ray Photoelectron Spectroscopy tests. The interaction was found to be based on the reversible formation of HxVO2 bronze, along with the reversible variations in the oxidation state of V.

Proton Conducting Neuromorphic Materials and Devices

Neuromorphic computing and artificial intelligence hardware generally aims to emulate features found in biological neural circuit components and to enable the development of energy-efficient machines. In the biological brain, ionic currents and temporal concentration gradients control information flow and storage. It is therefore of interest to examine materials and devices for neuromorphic computing wherein ionic and electronic currents can propagate. Protons being mobile under an external electric field offers a compelling avenue for facilitating biological functionalities in artificial synapses and neurons. In this review, we first highlight the interesting biological analog of protons as neurotransmitters in various animals. We then discuss the experimental approaches and mechanisms of proton doping in various classes of inorganic and organic proton-conducting materials for the advancement of neuromorphic architectures. Since hydrogen is among the lightest of elements, characterization in a solid matrix requires advanced techniques. We review powerful synchrotron-based spectroscopic techniques for characterizing hydrogen doping in various materials as well as complementary scattering techniques to detect hydrogen. First-principles calculations are then discussed as they help provide an understanding of proton migration and electronic structure modification. Outstanding scientific challenges to further our understanding of proton doping and its use in emerging neuromorphic electronics are pointed out.

Switchable and Tunable Radiative Cooling: Mechanisms, Applications, and Perspectives

The cost of annual energy consumption in buildings in the United States exceeds 430 billion dollars ( Science 2019, 364 (6442), 760-763), of which about 48% is used for space thermal management (https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019), revealing the urgent need for efficient thermal management of buildings and dwellings. Radiative cooling technologies, combined with the booming photonic and microfabrication technologies ( Nature 2014, 515 (7528), 540-544), enable energy-free cooling by radiative heat transfer to outer space through the atmospheric transparent window ( Nat. Commun. 2024, 15 (1), 815). To pursue all-season energy savings in climates with large temperature variations, switchable and tunable radiative coolers (STRC) have emerged in recent years and quickly gained broad attention. This Perspective introduces the existing STRC technologies and analyzes their benefits and challenges in future large-scale applications, suggesting ways for the development of future STRCs.

Ion diffusion retarded by diverging chemical susceptibility

For first-order phase transitions, the second derivatives of Gibbs free energy (specific heat and compressibility) diverge at the transition point, resulting in an effect known as super-elasticity along the pressure axis, or super-thermicity along the temperature axis. Here we report a chemical analogy of these singularity effects along the atomic doping axis, where the second derivative of Gibbs free energy (chemical susceptibility) diverges at the transition point, leading to an anomalously high energy barrier for dopant diffusion in co-existing phases, an effect we coin as super-susceptibility. The effect is realized in hydrogen diffusion in vanadium dioxide (VO2) with a metal-insulator transition (MIT). We show that hydrogen faces three times higher energy barrier and over one order of magnitude lower diffusivity when it diffuses across a metal-insulator domain wall in VO2. The additional energy barrier is attributed to a volumetric energy penalty that the diffusers need to pay for the reduction of latent heat. The super-susceptibility and resultant retarded atomic diffusion are expected to exist universally in all phase transformations where the transformation temperature is coupled to chemical composition, and inspires new ways to engineer dopant diffusion in phase-coexisting material systems.

Spatial evolution of the proton-coupled Mott transition in correlated oxides for neuromorphic computing

The proton-electron coupling effect induces rich spectrums of electronic states in correlated oxides, opening tempting opportunities for exploring novel devices with multifunctions. Here, via modest Pt-aided hydrogen spillover at room temperature, amounts of protons are introduced into SmNiO3-based devices. In situ structural characterizations together with first-principles calculation reveal that the local Mott transition is reversibly driven by migration and redistribution of the predoped protons. The accompanying giant resistance change results in excellent memristive behaviors under ultralow electric fields. Hierarchical tree-like memory states, an instinct displayed in bio-synapses, are further realized in the devices by spatially varying the proton concentration with electric pulses, showing great promise in artificial neural networks for solving intricate problems. Our research demonstrates the direct and effective control of proton evolution using extremely low electric field, offering an alternative pathway for modifying the functionalities of correlated oxides and constructing low-power consumption intelligent devices and neural network circuits.

Multifield-Modulated Spintronic Terahertz Emitter Based on a Vanadium Dioxide Phase Transition

The efficient generation and active modulation of terahertz (THz) waves are strongly required for the development of various THz applications such as THz imaging/spectroscopy and THz communication. In addition, due to the increasing degree of integration for the THz optoelectronic devices, miniaturizing the complex THz system into a compact unit is also important and necessary. Today, integrating the THz source with the modulator to develop a powerful, easy-to-adjust, and scalable or on-chip THz emitter is still a challenge. As a new type of THz emitter, a spintronic THz emitter has attracted a great deal of attention due to its advantages of high efficiency, ultrawide band, low cost, and easy integration. In this study, we have proposed a multifield-modulated spintronic THz emitter based on the VO2/Ni/Pt multilayer film structure with a wide band region of 0-3 THz. Because of the pronounced phase transition of the integrated VO2 layer, the fabricated THz emitter can be efficiently modulated via thermal or electric stimuli with a modulation depth of about one order of magnitude; the modulation depths under thermal stimulation and electrical stimulation were 91.8% and 97.3%, respectively. It is believed that this multifield modulated spintronic THz emitter will provide various possibilities for the integration of next-generation on-chip THz sources and THz modulators.

Strain-Induced Uphill Hydrogen Distribution in Perovskite Oxide Films

Incorporating hydrogen into transition-metal oxides (TMOs) provides a facile and powerful way to manipulate the performances of TMOs, and thus numerous efforts have been invested in developing hydrogenation methods and exploring the property modulation via hydrogen doping. However, the distribution of hydrogen ions, which is a key factor in determining the physicochemical properties on a microscopic scale, has not been clearly illustrated. Here, focusing on prototypical perovskite oxide (NdNiO3 and La0.67Sr0.33MnO3) epitaxial films, we find that hydrogen distribution exhibits an anomalous "uphill" feature (against the concentration gradient) under tensile strain, namely, the proton concentration enhances upon getting farther from the hydrogen source. Distinctly, under a compressive strain state, hydrogen shows a normal distribution without uphill features. The epitaxial strain significantly influences the chemical lattice coupling and the energy profile as a function of the hydrogen doping position, thus dominating the hydrogen distribution. Furthermore, the strain-(H+) distribution relationship is maintained in different hydrogenation methods (metal-alkali treatment) which is first applied to perovskite oxides. The discovery of strain-dependent hydrogen distribution in oxides provides insights into tailoring the magnetoelectric and energy-conversion functionalities of TMOs via strain engineering.

Protonation-Induced Colossal Lattice Expansion in La2/3Sr1/3MnO3

Ion injection controlled by an electric field is a powerful method to manipulate the diverse physical and chemical properties of metal oxides. However, the dynamic control of ion concentrations and their correlations with lattices in perovskite systems have not been fully understood. In this study, we systematically demonstrate the electric-field-controlled protonation of La2/3Sr1/3MnO3 (LSMO) films. The rapid and room-temperature protonation induces a colossal lattice expansion of 9.35% in tensile-strained LSMO, which is crucial for tailoring material properties and enabling a wide range of applications in advanced electronics, energy storage, and sensing technologies. This large expansion in the lattice is attributed to the higher degree of proton diffusion, resulting in a significant elongation in the Mn-O bond and octahedral tilting, which is supported by results from density functional theory calculations. Interestingly, such a colossal expansion is not observed in LSMO under compressive strain, indicating the close dependence of ion-electron-lattice coupling on strain states. These efficient modulations of the lattice and magnetoelectric functionalities of LSMO via proton diffusion offer a promising avenue for developing multifunctional iontronic devices.

Chemical Modulation of Metal-Insulator Transition toward Multifunctional Applications in Vanadium Dioxide Nanostructures

The metal-insulator transition (MIT) of vanadium dioxide (VO2 ) has been of great interest in materials science for both fundamental understanding of strongly correlated physics and a wide range of applications in optics, thermotics, spintronics, and electronics. Due to the merits of chemical interaction with accessibility, versatility, and tunability, chemical modification provides a new perspective to regulate the MIT of VO2 , endowing VO2 with exciting properties and improved functionalities. In the past few years, plenty of efforts have been devoted to exploring innovative chemical approaches for the synthesis and MIT modulation of VO2 nanostructures, greatly contributing to the understanding of electronic correlations and development of MIT-driven functionalities. Here, this comprehensive review summarizes the recent achievements in chemical synthesis of VO2 and its MIT modulation involving hydrogen incorporation, composition engineering, surface modification, and electrochemical gating. The newly appearing phenomena, mechanism of electronic correlation, and structural instability are discussed. Furthermore, progresses related to MIT-driven applications are presented, such as the smart window, optoelectronic detector, thermal microactuator, thermal radiation coating, spintronic device, memristive, and neuromorphic device. Finally, the challenges and prospects in future research of chemical modulation and functional applications of VO2 MIT are also provided.

Ultrahigh Effective Diffusion in Oxide by Engineering the Interfacial Transporter Channels

Mass storage and removal in solids always play a vital role in technological applications such as modern batteries and neuronal computations. However, they were kinetically limited by the slow diffusional process in the lattice, which made it challenging to fabricate applicable conductors with high electronic and ionic conductivities at room temperature. Here, we proposed an acid solution/WO3/ITO sandwich structure and achieved ultrafast H transport in the WO3 layer by interfacial job-sharing diffusion, which means the spatially separated transport of the H+ and e- in different layers. From the color change of WO3, the effective diffusion coefficient (Deff) was estimated, dramatically increasing ≤106 times and overwhelming values from previous reports. The experiments and simulations also revealed the universality of extending this approach to other atoms and oxides, which could stimulate systematic studies of ultrafast mixed conductors in the future.

Nanostructured Vanadium Dioxide Materials for Optical Sensing Applications

Vanadium dioxide (VO2) is one of the strongly correlated materials exhibiting a reversible insulator-metal phase transition accompanied by a structural transition from a low-temperature monoclinic phase to high-temperature rutile phase near room temperature. Due to the dramatic change in electrical resistance and optical transmittance of VO2, it has attracted considerable attention towards the electronic and optical device applications, such as switching devices, memory devices, memristors, smart windows, sensors, actuators, etc. The present review provides an overview of several methods for the synthesis of nanostructured VO2, such as solution-based chemical approaches (sol-gel process and hydrothermal synthesis) and gas or vapor phase synthesis techniques (pulsed laser deposition, sputtering method, and chemical vapor deposition). This review also presents stoichiometry, strain, and doping engineering as modulation strategies of physical properties for nanostructured VO2. In particular, this review describes ultraviolet-visible-near infrared photodetectors, optical switches, and color modulators as optical sensing applications associated with nanostructured VO2 materials. Finally, current research trends and perspectives are also discussed.

Selective area doping for Mott neuromorphic electronics

The cointegration of artificial neuronal and synaptic devices with homotypic materials and structures can greatly simplify the fabrication of neuromorphic hardware. We demonstrate experimental realization of vanadium dioxide (VO₂) artificial neurons and synapses on the same substrate through selective area carrier doping. By locally configuring pairs of catalytic and inert electrodes that enable nanoscale control over carrier density, volatility or nonvolatility can be appropriately assigned to each two-terminal Mott memory device per lithographic design, and both neuron- and synapse-like devices are successfully integrated on a single chip. Feedforward excitation and inhibition neural motifs are demonstrated at hardware level, followed by simulation of network-level handwritten digit and fashion product recognition tasks with experimental characteristics. Spatially selective electron doping opens up previously unidentified avenues for integration of emerging correlated semiconductors in electronic device technologies.

Elucidation of a Photothermal Energy Conversion Mechanism in Hydrogenated Molybdenum Suboxide: Interplay of Trapped Charges and Their Dielectric Interactions

Hydrogenated molybdenum suboxide (H_xMoO_3-y) is a promising photothermal energy conversion (PEC) material. However, its charge carrier dynamics and underlying mechanisms remain unclear. Utilizing flash-photolysis time-resolved microwave conductivity, we investigated charge carrier-dielectric interactions in the Pt/H_xMoO_3-y composite. The charge recombination of H₂-reduced Pt/H_xMoO_3-y was 2-3 orders of magnitude faster than that of Pt/MoO₃, indicating efficient PEC. A complex photoconductivity study revealed that Pt/H_xMoO_3-y has two types of trapping mechanisms, Drude-Zener (DZ) and negative permittivity effect (NPE) modes, depending on the reduction temperature. Pt/H_xMoO_3-y reduced at 100 °C exhibited a dominant NPE owing to the electrical interaction of trapped charges with the surrounding ions and/or OH base. This polaronic trapped state retarded the PEC process. We found Pt/H_xMoO_3-y reduced at 200 °C to be optimal owing to the balanced suppression of the NPE and charge diffusion. This is the first report revealing the charge dynamics in hydrogenated metal oxides and their impacts on PEC processes.

Regioselectivity of concerted proton-electron transfer at the surface of a polyoxovanadate cluster

Proton-coupled electron transfer (PCET) is an important process in the activation and reactivity of metal oxide surfaces. In this work, we study the electronic structure of a reduced polyoxovanadate-alkoxide cluster bearing a single bridging oxide moiety. The structural and electronic implications of the incorporation of bridging oxide sites are revealed, most notably resulting in the quenching of cluster-wide electron delocalization in the most reduced state of the molecule. We correlate this attribute to a change in regioselectivity of PCET to the cluster surface (e.g. reactivity at terminal vs. bridging oxide groups). Reactivity localized at the bridging oxide site enables reversible storage of a single H-atom equivalent, changing the stoichiometry of PCET from a 2e-/2H+ process. Kinetic investigations indicate that the change in site of reactivity translates to an accelerated rate of e-/H+ transfer to the cluster surface. Our work summarizes the role which electronic occupancy and ligand density play in the uptake of e-/H+ pairs at metal oxide surfaces, providing design criteria for functional materials for energy storage and conversion processes.

Realizing Metastable Cobaltite Perovskite via Proton-Induced Filling of Oxygen Vacancy Channels

The interaction between transition-metal oxides (TMOs) and protons has become a key issue in magneto-ionics and proton-conducting fuel cells. Until now, most investigations on oxide-proton reactions rely on electrochemical tools, while the direct interplay between protons and oxides remains basically at simple dissolution of metal oxides by an acidic solution. In this work, we find classical TMO brownmillerite SrCoO_2.5 (B-SCO) films with ordered oxygen vacancy channels experiencing an interesting transition to a metastable perovskite phase (M-SCO) in a weak acidic solution. M-SCO exhibits a strong ferromagnetism (1.01 μ_B/Co, T_c > 200 K) and a greatly elevated electrical conductivity (∼10⁴ of pristine SrCoO_2.5), which is similar to the prototypical perovskite SrCoO₃. Besides, such M-SCO tends to transform back to B-SCO in a vacuum environment or heating at a relatively low temperature. Two possible mechanisms (H₂O addition/active oxygen filling) have been proposed to explain the phenomenon, and the control experiments demonstrate that the latter mechanism is the dominant process. Our work finds a new way to realize cobaltite perovskite with enhanced magnetoelectric properties and may deepen the understanding of oxide-proton interaction in an aqueous solution.

Basal Planes Unlocking and Interlayer Engineering Endows Proton Doped-MoO2.8F0.2 with Fast and Stable Magnesium Storage

Molybdenum trioxide has served as a promising cathode material of rechargeable magnesium batteries (RMBs), because of its rich valence states and high theoretical capacity; yet, it still suffers from sluggish (de)intercalation kinetics and inreversible structure change for highly polarized Mg²⁺ in the interlayer and intralayer of structure. Herein, F^- substitutional and H⁺ interstitial doping is proposed for α-MoO₃ materials (denoted HMoOF) by the intralayer/interlayer engineering strategy to boost the performance of RMBs. F^- substitutional doping generates molybdenum vacancies along the Mo-O-□ or Mo-F-□ configurations (where □ represents the cationic vacancy) for unlocking the inactive basal plane of the layered crystal structure, and it further accelerates Mg²⁺ diffusion along the b-axis. Interstitial-doped H⁺ can expand interlayer spacing for reducing Mg²⁺ energy barrier along the ac plane and serve as a "pillar" to stabilize the interlayer structure. Moreover, anion and cation dual doping trigger shallow impurity levels (acceptors levels and donor levels), which helps to easily acquire the electrons from the valence band and donate the electrons to the conduction band. Consequently, the HMoOF electrode exhibits a high reversible capacity (241 mA h g^-1 at 0.1 A g^-1), an excellent rate capability (137.4 mAh g^-1 at 2 A g^-1), and a long cycling stability (capacity retention of 98% after 800 cycles at 1 A g^-1) in RMBs. This work affords meaningful insights in layered materials for developing high-kinetics and long-life RMBs.

Revealing the Role of Hydrogen in Electron-Doping Mottronics for Strongly Correlated Vanadium Dioxide

Hydrogen-associated electron-doping Mottronics for d-band correlated oxides (e.g., VO₂) opens up a new paradigm to regulate the electronic functionality via directly manipulating the orbital configuration and occupancy. Nevertheless, the role of hydrogen in the Mottronic transition of VO₂ is yet unclear because opposite orbital reconfigurations toward either the metallic or highly insulating states were both reported. Herein, we demonstrate the root cause for such hydrogen-induced multiple electronic phase transitions by ¹H quantification using nuclear reaction analysis. A low hydrogenation temperature is demonstrated to be vital in achieving a large hydrogen concentration (n_H ≈ 10²² cm^-3) that further enhances the t_2g orbital occupancy to trigger electron localizations. In contrast, elevating the hydrogenation temperatures surprisingly reduces n_H to ∼10²¹ cm^-3 but forms more stable metallic H_0.06VO₂. This leads to the recognition of a weaker hydrogen interaction that triggers electron localization within VO₂ via Mottronically enhancing the orbital occupancies.

Connecting Thermodynamics and Kinetics of Proton Coupled Electron Transfer at Polyoxovanadate Surfaces Using the Marcus Cross Relation

Here, we evaluate the efficacy of multiple methods for elucidating the average bond dissociation free energy (BDFE) of two surface hydroxide moieties in a reduced polyoxovanadate cluster, [V₆O₁₁(OH)₂(TRIOL^NO2)₂]^-2. Through cyclic voltammetry, individual thermochemical parameters describing proton coupled electron transfer (PCET) are obtained, without the need for synthetic isolation of intermediates. Further, we demonstrate that a method involving a series of open circuit potential measurements with varying ratios of reduced to oxidized clusters is most attractive for the direct measurement of BDFE(O-H) for polyoxovanadate clusters as this approach also determines the stoichiometry of PCET. We subsequently connect the driving force of PCET to the rate constant for the transfer of hydrogen atoms to a series of organic substrates through the Marcus cross relation. We show that this method is applicable for the prediction of reaction rates for multielectron/multiproton transfer reactions, extending the findings from previous work focused on single electron/proton reactions.

Charge-State Dependence of Proton Uptake in Polyoxovanadate-alkoxide Clusters

Here, we present an investigation of the thermochemistry of proton uptake in acetonitrile across three charge states of a polyoxovanadate-alkoxide (POV-alkoxide) cluster, [V6O7(OMe)12]n (n = 2-, 1-, and 0). The vanadium oxide assembly studied features bridging sites saturated by methoxide ligands, isolating protonation to terminal vanadyl moieties. Exposure of [V6O7(OMe)12]n to organic acids of appropriate strength results in the protonation of a terminal V═O bond, generating the transient hydroxide-substituted POV-alkoxide cluster [V6O6(OH)(OMe)12]n+1. Evidence for this intermediate proved elusive in our initial report, but here we present the isolation of a divalent anionic cluster that features hydrogen bonding to dimethylammonium at the terminal oxo site. Degradation of the protonated species results in the formation of equimolar quantities of one-electron-oxidized and oxygen-atom-efficient complexes, [V6O7(OMe)12]n+1 and [V6O6(OMe)12]n+1. While analogous reactivity was observed across the three charge states of the cluster, a dependence on the acid strength was observed, suggesting that the oxidation state of the vanadium oxide assembly influences the basicity of the cluster surface. Spectroscopic investigations reveal sigmoidal relationships between the acid strength and cluster conversion across the redox series, allowing for determination of the proton affinity of the surface of the cluster in all three charge states. The fully reduced cluster is found to be the most basic, with higher oxidation states of the assembly possessing substantially reduced proton affinities (∼7 pKa units per electron). These results further our understanding of the site-specific reactivity of terminal M═O bonds with protons in an organic solvent, revealing design criteria for engineering functional surfaces of metal oxide materials of relevance to energy storage and conversion.

Oxygen-Atom Defect Formation in Polyoxovanadate Clusters via Proton-Coupled Electron Transfer

The uptake of hydrogen atoms (H-atoms) into reducible metal oxides has implications in catalysis and energy storage. However, outside of computational modeling, it is difficult to obtain insight into the physicochemical factors that govern H-atom uptake at the atomic level. Here, we describe oxygen-atom vacancy formation in a series of hexavanadate assemblies via proton-coupled electron transfer, presenting a novel pathway for the formation of defect sites at the surface of redox-active metal oxides. Kinetic investigations reveal that H-atom transfer to the metal oxide surface occurs through concerted proton-electron transfer, resulting in the formation of a transient VIII-OH2 moiety that, upon displacement of the water ligand with an acetonitrile molecule, forms the oxygen-deficient polyoxovanadate-alkoxide cluster. Oxidation state distribution of the cluster core dictates the affinity of surface oxido ligands for H-atoms, mirroring the behavior of reducible metal oxide nanocrystals. Ultimately, atomistic insights from this work provide new design criteria for predictive proton-coupled electron-transfer reactivity of terminal M═O moieties at the surface of nanoscopic metal oxides.

Ultrafast and Low-Threshold THz Mode Switching of Two-Dimensional Nonlinear Metamaterials

Judiciously designed two-dimensional THz metamaterials consisting of resonant metallic structures embedded in a dielectric environment locally enhance the electromagnetic field of an incident THz pulse to values sufficiently high to cause nonlinear responses of the environment. In semiconductors, the response is attributed to nonlinear transport phenomena via intervalley scattering, impact ionization, or interband tunneling and can affect the resonant behavior of the metallic structure, which results, for instance, in mode switching. However, details of mode switching, especially time scales, are still debated. By using metallic split-ring resonators with nm-size gaps on intrinsic semiconductors with different bandgaps, we identify the most relevant carrier generation processes. In addition, by combining nonlinear THz time-domain spectroscopy with simulations, we establish the fastest time constant for mode switching to around hundred femtoseconds. Our results not only elucidate dominant carrier generation mechanisms and dynamics but also pave the route toward optically driven modulators with THz bandwidth.

The mechanism of semiconductor to metal transition in the hydrogenation of VO2: A density functional theory study

VO2 is a glamorous material with specific metal-semiconductor-transition (MST). The hydrogenation of VO2 could make it a promising material applying in the ambient environment. In this work, we reveal the...

Wafer-scale freestanding vanadium dioxide film

Vanadium dioxide (VO₂), with well-known metal-to-insulator phase transition, has been used to realize intriguing smart functions in photodetectors, modulators, and actuators. Wafer-scale freestanding VO₂ (f-VO₂) films are desirable for integrating VO₂ with other materials into multifunctional devices. Unfortunately, their preparation has yet to be achieved because the wafer-scale etching needs ultralong time and damages amphoteric VO₂ whether in acid or alkaline etchants. Here, we achieved wafer-scale f-VO₂ films by a nano-pinhole permeation-etching strategy in 6 min, far less than that by side etching (thousands of minutes). The f-VO₂ films retain their pristine metal-to-insulator transition and intrinsic mechanical properties and can be conformably transferred to arbitrary substrates. Integration of f-VO₂ films into diverse large-scale smart devices, including terahertz modulators, camouflageable photoactuators, and temperature-indicating strips, shows advantages in low insertion loss, fast response, and low triggering power. These f-VO₂ films find more intriguing applications by heterogeneous integration with other functional materials.

Photoassisted Electron-Ion Synergic Doping Induced Phase Transition of n-VO2/p-GaN Thin-Film Heterojunction

As a typical correlated metal oxide, vanadium dioxide (VO₂) shows specific metal-insulator transition (MIT) properties and demonstrates great potential applications in ultrafast optoelectronic switch, resistive memory, and neuromorphic devices. Effective control of the MIT process is essential for improving the device performance. In the current study, we have first proposed a photoassisted ion-doping method to modulate the phase transition of the VO₂ layer based on the photovoltaic effect and electron-ion synergic doping in acid solution. Experimental results show that, for the prepared n-VO₂/p-GaN nanojunction, this photoassisted strategy can effectively dope the n-VO₂ layer by H⁺, Al³⁺, or Mg²⁺ ions under light radiation and trigger consecutive insulator-metal-insulator transitions. If combined with standard lithography or electron beam etching processes, selective doping with nanoscale size area can also be achieved. This photoassisted doping method not only shows a facile route for MIT modulation via a doping route under ambient conditions but also supplies some clues for photosensitive detection in the future.

Direct Electrochemical Protonation of Metal Oxide Particles

Metal oxides with surface protonation exhibit versatile physical and chemical properties suitable for use in many fields. Here, we develop an electrochemical route to directly protonize the physically assembled oxide particles, such as TiO₂, Nb₂O₅, and WO₃, in a Na₂SO₄ neutral electrolyte, which is a result of electrochemically induced oxygen vacancies reacting with water molecules. With no need of electric connection among particles or between particles and conductive substrate, the electrochemical protonation follows a bottom-up particle-by-particle surface protonation mechanism due to the fact that the protonation inducing high surface conductivity creates an efficient electron transfer pathway among particles. Our results show that electrochemical protonation of particles provides a chance to finely functionalize the surface of a single particle by only adjusting electrode potentials. Such a facile, cost-efficient, and green route is easy to run for a large-scale production and unlocks the potential of semiconductor oxides for various applications.

Reversible Rapid Hydrogen Doping of WO3 in Non-Acid Solution

Hydrogenation, an effective way to tune the properties of transition metal oxide (TMO) thin films, has been long awaited to be performed safely and without an external energy input. Recently, metal-acid-TMO has been reported to be an effective approach for hydrogenation, but the requirement of acid limits its application. In this work, the reversible and rapid hydrogen doping of WO₃ in NaOH(aq) | Al(s) | WO₃(s) is revealed by structural and electrical measurements. Accompanied by the structural phase transition identified by in situ X-ray diffraction, the electric resistance of the WO₃ film is found to be able to change by 5 orders of magnitude. A significant electrical response of touching, 8-fold in amplitude and 3 s in a cycle, can be achieved in the low-resistance state. These reactions are reversible at room temperature. This study unambiguously proves that the hydrogenation-driven dynamic phase transition of WO₃ in metal-solution-WO₃ systems could occur not only in acid solutions but also in some non-acid environments. Unlike the monotonic increase of resistance revealed during H_δWO₃ to WO₃ transition, an intriguing non-monotonic evolution was found for crystal lattice parameter c, indicating that the mechanism of WO₃ hydrogenation involves a series of metastable states, more comprehensive and reasonable. This work sheds light on the potential applications of metal-solution-TMO hydrogenation in touching sensors, circuits survey, and information storage.

Surface/Interface Chemistry Engineering of Correlated-Electron Materials: From Conducting Solids, Phase Transitions to External-Field Response

Correlated electronic materials (CEMs) with strong electron-electron interactions are often associated with exotic properties, such as metal-insulator transition (MIT), charge density wave (CDW), superconductivity, and magnetoresistance (MR), which are fundamental to next generation condensed matter research and electronic devices. When the dimension of CEMs decreases, exposing extremely high specific surface area and enhancing electronic correlation, the surface states are equally important to the bulk phase. Therefore, surface/interface chemical interactions provide an alternative route to regulate the intrinsic properties of low-dimensional CEMs. Here, recent achievements in surface/interface chemistry engineering of low-dimensional CEMs are reviewed, using surface modification, molecule-solid interaction, and interface electronic coupling, toward modulation of conducting solids, phase transitions including MIT, CDW, superconductivity, and magnetism transition, as well as external-field response. Surface/interface chemistry engineering provides a promising strategy for exploring novel properties and functional applications in low-dimensional CEMs. Finally, the current challenge and outlook of the surface/interface engineering are also pointed out for future research development.

Reductive silylation of polyoxovanadate surfaces using Mashima's reagent

Mechanistic insights into the reductive silylation of metal oxide surfaces.

Atomic Origin for Hydrogenation Promoted Bulk Oxygen Vacancies Removal in Vanadium Dioxide

Oxygen vacancies (V_O), a common type of point defect in metal oxides materials, play important roles in the physical and chemical properties. To obtain stoichiometric oxide crystal, the pre-existing V_O is always removed via careful post-annealing treatment at high temperature in an air or oxygen atmosphere. However, the annealing conditions are difficult to control, and the removal of V_O in the bulk phase is restrained because of the high energy barrier of V_O migration. Here, we selected VO₂ crystal film as the model system and developed an alternative annealing treatment aided by controllable hydrogen doping, which can realize effective removal of V_O defects in the VO_2-δ crystal at a lower temperature. This finding is attributed to the hydrogenation accelerated oxygen vacancies recovery in the VO_2-δ crystal. Theoretical calculations revealed that the H-doping-induced electrons are prone to accumulate around the oxygen defects in the VO_2-δ film, which facilitates the diffusion of V_O and thus makes it easier to be removed. The methodology is expected to be applied to other metal oxides for oxygen-related point defects control.

Hydrogen-Doping-Induced Metal-Like Ultrahigh Free-Carrier Concentration in Metal-Oxide Material for Giant and Tunable Plasmon Resonance

The practical utilization of plasmon-based technology relies on the ability to find high-performance plasmonic materials other than noble metals. A key scientific challenge is to significantly increase the intrinsically low concentration of free carriers in metal-oxide materials. Here, a novel electron-proton co-doping strategy is developed to achieve uniform hydrogen doping in metal-oxide MoO₃ at mild conditions, which creates a metal-like ultrahigh free-carrier concentration approaching that of noble metals (10²¹ cm^-3 in H_1.68 MoO₃ versus 10²² cm^-3 in Au/Ag). This bestows giant and tunable plasmonic resonances in the visible region to this originally semiconductive material. Using ultrafast spectroscopy characterizations and first-principle simulations, the formation of a quasi-metallic energy band structure that leads to long-lived and strong plasmonic field is revealed. As verified by the surface-enhanced Raman spectra (SERS) of rhodamine 6G molecules on H_x MoO₃ , the SERS enhancement factor reaches as high as 1.1 × 10⁷ with a detection limit at concentration as low as 1 × 10^-9  mol L^-1 , representing the best among the hitherto reported non-metal systems. The findings not only provide a set of metal-like semiconductor materials with merits of low cost, tunable electronic structure, and plasmonic resonance, but also a general strategy to induce tunable ultrahigh free-carrier concentration in non-metal systems.

Reconfigurable Multistate Optical Systems Enabled by VO2 Phase Transitions

Reconfigurable optical systems are the object of continuing, intensive research activities, as they hold great promise for realizing a new generation of compact, miniaturized, and flexible optical devices. However, current reconfigurable systems often tune only a single state variable triggered by an external stimulus, thus, leaving out many potential applications. Here we demonstrate a reconfigurable multistate optical system enabled by phase transitions in vanadium dioxide (VO₂). By controlling the phase-transition characteristics of VO₂ with simultaneous stimuli, the responses of the optical system can be reconfigured among multiple states. In particular, we show a quadruple-state dynamic plasmonic display that responds to both temperature tuning and hydrogen-doping. Furthermore, we introduce an electron-doping scheme to locally control the phase-transition behavior of VO₂, enabling an optical encryption device encoded by multiple keys. Our work points the way toward advanced multistate reconfigurable optical systems, which substantially outperform current optical devices in both breadth of capabilities and functionalities.

Acid-Induced, Oxygen-Atom Defect Formation in Reduced Polyoxovanadate-Alkoxide Clusters

Here, we present the first example of acid-induced, oxygen-atom abstraction from the surface of a polyoxometalate cluster. Generation of the oxygen-deficient vanadium oxide, [V₆O₆(OC₂H₅)₁₂]^1-, was confirmed via independent synthesis. Spectroscopic analysis using infrared and electronic absorption spectroscopies affords resolution of the electronic structure of the oxygen-deficient cluster (oxidation state distribution = [V^IIIV^IV₅]). This work has direct implications toward the elucidation of possible mechanisms of acid-assisted vacancy formation in bulk transition metal oxides, in particular electron-proton codoping that has recently been described for vanadium oxide (VO₂). Ultimately, these molecular models deepen our understanding of proton-dependent redox chemistry of transition metal oxide surfaces.

A Hydrogenated Metal Oxide with Full Solar Spectrum Absorption for Highly Efficient Photothermal Water Evaporation

Searching for cost-effective photothermal material that can harvest the full solar spectrum is critically important for solar-driven water evaporation. Metal oxides are cheap materials but cannot cover the full solar spectrum. Here we prepared a hydrogenated metal oxide (H_1.68MoO₃) material, in which H-doping causes the insulator-to-metal phase transition of the originally semiconductive MoO₃. It offers a blackbody-like solar absorption of ≥95% over the entire visible-to-near-infrared solar spectrum, owing to its unusual quasi-metallic energy band, and high solar-to-heat conversion rate due to quick relaxation of excited electrons. Using a self-floating H_1.68MoO₃/airlaid paper photothermal film, we achieved a stable and high water vapor generation rate of 1.37 kg m^-2 h^-1, a superb solar-to-vapor efficiency of 84.8% under 1 sun illumination, and daily production of 12.4 L of sanitary water/m² from seawater under natural sunlight. This thus opens a new avenue of designing cost-effective photothermal materials based on metal oxides.

Tunable Hydrogen Doping of Metal Oxide Semiconductors with Acid-Metal Treatment at Ambient Conditions

Hydrogen doping of metal oxide semiconductors is promising for manipulation of their properties toward various applications. Yet it is quite challenging because it requires harsh reaction conditions and expensive metal catalysts. Meanwhile, acids as a cheap source of protons have long been unappreciated. Here, we develop a sophisticated acid-metal treatment for tunable hydrogenation of metal oxides at ambient conditions. Using first-principles simulations, we first show that, with proper work function difference between the metal and metal oxide, H-diffusion into negatively charged metal oxide can be well controlled, resulting in tunable H-doping of metal oxides with quasi-metal characteristics. This has been verified by proof-of-concept experiments that achieved the controllable hydrogenation of WO₃ using Cu and hydrochloric acid at ambient conditions. Further, H-doping of other metal oxides (TiO₂/Nb₂O₅/MoO₃) has been achieved by metal-acid treatment and induced a change in properties. Our work provides a promising way to tailor metal oxides via tunable H-doping.

Tuning Phase Transitions in Metal Oxides by Hydrogen Doping: A First-Principles Study

Optimizing physical or chemical properties via electronic phase transitions is important for developing high-performance semiconductor materials. Using first-principles calculations, we established hydrogen doping (H-doping) as an alternative strategy for modulating phase transitions in metal oxide semiconductors. We found that H-doping can induce an insulator-to-metal phase transition in rutile TiO₂ or wurtzite ZnO, a metal-to-insulator phase transition in rutile VO₂, and sequential insulator-metal-insulator phase transitions in SnO₂. H-doping not only creates defect-induced states inside the original bandgap but also induces new occupancy patterns in conduction band edge states. A linear relationship between occupation of the conduction band edge and H-doping concentration was found, offering the possibility of precisely tuning the material's free-carrier concentration, electrical conductance, and photoabsorption ability. We envision that this work will provide a promising way to tune electrical phase transitions in metal oxides.

Oxygen-atom vacancy formation and reactivity in polyoxovanadate clusters

Overview of recent work detailing oxygen-deficient polyoxovanadate clusters as models for reducible metal oxides: toward gaining a fundamental understanding the consequences of vacancy formation on metal oxide surfaces during catalysis.

Enhanced charge storage properties of ultrananocrystalline diamond films by contact electrification-induced hydrogenation

We report the enhanced charge storage characteristics of ultrananocrystalline diamond (UNCD) by contact electrification-induced hydrogenation. The non-catalytic hydrogenation of UNCD films was achieved by using platinum as an electron donor and sulfuric acid as a hydrogen proton donor, confirmed by Raman spectroscopy and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Chemical treatment with only a H₂SO₄ solution is responsible for the surface oxidation. The oxidation of UNCD resulted in an increase in the quantity and duration of the tribocharges. After non-catalytic hydrogenation, the generation of friction-induced tribocharges was enhanced and remained for three hours and more. We show that the hydrogen incorporation on grain boundaries is responsible for the improvement of charge storage capability, because the doped hydrogen acts as a trap site for the tribocharges. This lab-scale and succinct method can be utilized to control charge trap capability in nanoscale memory electronics.

The enhanced charge storage characteristics of ultrananocrystalline diamond caused by contact electrification-induced hydrogenation was demonstrated by using atomic force microscopy.

Long-range propagation of protons in single-crystal VO2 involving structural transformation to HVO2

Vanadium dioxide (VO₂) is a strongly correlated electronic material with a metal-insulator transition (MIT) near room temperature. Ion-doping to VO₂ dramatically alters its transport properties and the MIT temperature. Recently, insulating hydrogenated VO₂ (HVO₂) accompanied by a crystal structure transformation from VO₂ was experimentally observed. Despite the important steps taken towards realizing novel applications, essential physics such as the diffusion constant of intercalated protons and the crystal transformation energy between VO₂ and HVO₂ are still lacking. In this work, we investigated the physical parameters of proton diffusion constants accompanied by VO₂ to HVO₂ crystal transformation with temperature variation and their transformation energies. It was found that protons could propagate several micrometers with a crystal transformation between VO₂ and HVO₂. The proton diffusion speed from HVO₂ to VO₂ was approximately two orders higher than that from VO₂ to HVO_2. The long-range propagation of protons leads to the possibility of realizing novel iontronic applications and energy devices.

Direct Probing of Oxygen Loss from the Surface Lattice of Correlated Oxides during Hydrogen Spillover

Hydrogen spillover is a catalytic process that occurs by surface reaction and subsequent diffusion to reversibly provide a massive amount of hydrogen dopants in correlated oxides, but the mechanism at the surface of correlated oxides with metal catalyst are not well understood. Here we show that a significant amount of oxygen is released from the surface of correlated VO₂ films during hydrogen spillover, contrary to the well-established observation of the formation of hydrogen interstitials in the bulk part of VO₂ films. By using ambient-pressure X-ray photoelectron spectroscopy, we prove that the formation of surface oxygen vacancies is a consequence of a favorable reaction for the generation of weakly adsorbed H₂O from surface O atoms that have low coordination and weak binding strength. Our results reveal the importance of in situ characterization to prove the dynamic change during redox reaction and present an opportunity to control intrinsic defects at the surface.

Electrons-Donating Derived Dual-Resistant Crust of VO2 Nano-Particles via Ascorbic Acid Treatment for Highly Stable Smart Windows Applications

Traditional vanadium dioxide (VO₂) material faced severe challenges of low stability in acid, humid, and oxygenic environments, which hinder its real applications. Here, we report a facile improving process which can enhanced the stability of VO₂ nanocrystals in the environments above. Ascorbic acid (AA), as an important antioxidant for organism in medicine and biology, was ingeniously used for enhancing the antioxidation abilities of inorganic material. At the same time, the AA could generate the hydrogen doping occurred on the surface of VO₂ nanocrystals, which enhanced their Antiacid abilities simultaneously. The AA treated VO₂ nanocrystals retain stable in H₂SO₄ and H₂O₂ solution and exhibit high durability in hyperthermal (60 °C) and humid (90%) environment. Characterizations and first-principles theoretical calculations confirmed that the coordination of ascorbic acid molecules on VO₂ nanocrystals induced charge-carrier density reorganization and protons transferring electrostatically. Then the formed H_xVO₂ provides an enhancing formation energy for oxygen vacancy and protects the particles from corrosion. This work is beneficial to the VO₂ nanoparticles coated and decorated processes and exhibit good potential for practical application of VO₂-based smart windows.