Vacancy Engineering Research Articles

Vacancy engineering in transition metal sulfide and oxide composite material for thermal batteries of high specific capacity

As a thermal battery cathode material, WS2 has high decomposition temperature and large specific capacity, but its low voltage problem has been rarely reported. In this work, we first prepared WS2 containing sulfur vacancies and then used it as a precursor to prepare a mixture of sulfur-vacancy and oxygen-vacancy double-doped WO3 with WS2 (WS2-x-WO3-x). WO3 was attached to the surface of WS2, which made the samples easier to be pressed into tablets. The presence of vacancies was confirmed by x-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR). The discharge results show that the discharge time of WS2-x-WO3-x is 52% higher than that of WS2. This work provides a beginning for further applying transition metal sulfide and oxide composite material for high capacity thermal batteries.

Unraveling a trade-off between positive effect and poisoning mechanism of soot over low-dose PtCu/CeO2 for simultaneously photothermocatalytic removal of VOCs and soot

It is challenging for simultaneous removal of VOCs and soot as soot would aggravate coke formation, and the lack of a deep understanding of pollutant effect on catalyst textural properties seriously limit its application. Herein, efficiently photothermocatalytic simultaneous removal of VOCs and soot was achieved by optimizing coke resistance and Pt utilization of PtCu/CeO2 through alloy modification and oxygen vacancy engineering. The findings of our combined experimental and computational study on catalytic process unravel a trade-off between positive effect and poisoning mechanism of soot, as follow: the unique photothermal properties and enhanced VOCs adsorption of soot accelerate VOCs degradation, while partially degraded soot passivate surface-active site of PtCu/CeO2 and weaken OH/O2 adsorption, thus suppressing VOCs mineralization. These new insights into the interfacial mechanism will provide a promising strategy to catalytic performance optimization and practical application.

Recent Advances in Co-Based Electrocatalysts for Hydrogen Evolution Reaction.

Water splitting is a promising technique in the sustainable "green hydrogen" generation to meet energy demands of modern society. Its industrial application is heavily dependent on the development of novel catalysts with high performance and low cost for hydrogen evolution reaction (HER). As a typical non-precious metal, cobalt-based catalysts have gained tremendous attention in recent years and shown a great prospect of commercialization. However, the complexity of the composition and structure of newly-developed Co-based catalysts make it urgent to comprehensively retrospect and summarize their advance and design strategies. Hence, in this review, the reaction mechanism of HER is first introduced and the possible role of the Co component during electrocatalysis is discussed. Then, various design strategies that could effectively enhance the intrinsic activity are summarized, including surface vacancy engineering, heteroatom doping, phase engineering, facet regulation, heterostructure construction, and the support effect. The recent progress of the advanced Co-based HER electrocatalysts is discussed, emphasizing that the application of the above design strategies can significantly improve performance by regulating the electronic structure and optimizing the binding energy to the crucial intermediates. At last, the prospects and challenges of Co-based catalysts are shown according to the viewpoint from fundamental explorations to industrial applications.

Engineering oxygen vacancy-rich CoAl layered double hydroxides coupled with N-doped carbon nanotubes as electrodes for supercapacitors

Layered double hydoxides (LDHs) as electrode materials for supercapacitors still suffer from unsatisfactory rate capability owing to their limited electrical conductivity and sluggish ion diffusion kinetics. In this work, a vacancy engineering strategy coupled with a nanocomposite method is proposed to construct oxygen vacancy (Ov)-rich CoAl-LDH nanosheets coupled with N-doped carbon nanotubes (N-CNTs) using a one-step precipitation-reduction reaction. Experimental analyses and theoretical calculation results indicate that the rich Ov defects in CoAl-LDHs not only effectively enhance the electrical conductivity but also reduce the surface adsorption barrier of electrolyte ions, thereby triggering fast charge storage kinetics. In addition, Ov-rich CoAl-LDH nanosheets coupled with N-CNTs are well dispersed, which not only enrich electroactive sites but also further increase the charge transport. Consequently, the obtained N-CNT@Ov-CoAl-LDH nanocomposites demonstrate a specific capacity of 1068 C g−1 at 3 A g−1 and maintain a capacity retention of 78% even at 20 A g−1, together with a capacity retention of 91% after 10,000 cycles at 10 A g−1. This work provides insights for designing and engineering LDHs-based electrodes with improved charge storage performance through coupling the vacancy engineering with the nanocomposite method.

Oxygen vacancy engineering of mesoporous Bi-Fe2O3@NC multi-channel microspheres for remarkable oxygen reduction and aqueous/flexible Zn-air batteries

Designing multi-channel mesoporous structure and introducing oxygen vacancies to synergistically enhance oxygen reduction reaction (ORR) activity is crucial for the practical application of zinc-air batteries (ZABs) in the field of energy storage and conversion. Herein, a novel multi-channel mesoporous Bi-Fe2O3 microsphere with abundant oxygen vacancies supported on nitrogen-doped carbon (denoted as Bi-Fe2O3@NC) is constructed and the designated catalyst demonstrates a higher half-wave potential (0.88 V), large limiting current density (5.8 mA cm−2@0.4 V), and superior stability. Besides, the aqueous ZAB utilizing Bi-Fe2O3@NC cathode achieves a high power density of 198.6 mW cm−2 and maintains exceptional stability for 459 h at 5 mA cm−2, superior to most previously reported catalysts. Furthermore, a solid-state ZAB assembled with Bi-Fe2O3@NC shows a power density of 55.9 mW cm−2, highlighting its potential for flexible ZAB applications. The prominent ORR performance of Bi-Fe2O3@NC can be ascribed to its unique multi-channel mesoporous structure and abundant oxygen vacancies, which increase the exposure of active sites and facilitate efficient electron/mass transport. This work provides valuable insights for the rational design of advanced ORR catalysts for the practical requirements of aqueous/flexible ZABs in energy storage and conversion.

Vacancy Augmented Piezo-Sonosensitizer for Cancer Therapy.

Sonodynamic therapy (SDT) has been widely reported as a noninvasive and high-penetration therapy for cancer; however, the design of an efficient sonosensitizer remains an urgent need. To address this issue, molybdenum disulfide nanoflowers (MoS2 NF) as piezo-sonosensitizers and introduced sulfur vacancies on the MoS2 NF (Sv-MoS2 NF) to improve their piezoelectric property for cancer therapy are designed. Under ultrasonic mechanical stress, the Sv-MoS2 NF resulted in piezoelectric polarization and band tilting, which enhanced the charge carrier separation and migration. This resulted in an improved catalytic reaction for reactive oxygen species (ROS) production, ultimately enhancing the SDT performance. Thanks to the high efficiency of ROS generation, the Sv-MoS2 NF have demonstrated a good anticancer effect in vitro and in vivo. Following a systematic evaluation, Sv-MoS2 NF also demonstrated good biocompatibility. This novel piezo-sonosensitizer and vacancy engineering strategy provides a promising new approach for achieving efficient SDT.

Vacancy engineering of MoS2−X @NCNTs for efficient storage of zinc ions

Zinc-ion batteries are receiving interest due to their high level of safety and eco-friendliness. However, the sluggish diffusion kinetics of zinc ions in the electrode limit its practical application. In this paper, rapid Zn2+ diffusion in the MoS2−X @NCNTs cathode is achieved by utilizing the S vacancies generated under a H2/Ar atmosphere and N-doped carbon nanotubes (NCNTs) derived from the pyrolysis of polyethylene and melamine. The presence of S vacancies significantly reduces the diffusion barrier of Zn2+, thereby promoting the transport of Zn2+ ions. MoS2−X @NCNTs cathode demonstrates an impressive discharge specific capacity of 220 mAh g−1 (0.1 A g−1) and a remarkable reversible capacity of 173 mAh g−1 (3 A g−1). Furthermore, the reduced adsorption energy of MoS2−X nanosheets leads to Zn2+ tending to preferentially insert S vacancies, resulting in a larger capacity than pure MoS2. This work realizes efficient storage of Zn2+ in 2D disulfides through carbon frameworks and S vacancies. In addition, flexible zinc batteries with MoS2−X @NCNTs cathodes have promising applications in wearable devices.

Oxygen vacancy engineering of TiO2 nanosheets for enhanced photothermal therapy against cervical cancer in the second near-infrared window

Cervical cancer is the most common and deadly female cancer on the worldwide scale. Considering that the conventional surgery treatment and chemotherapy would cause certain side effects, photothermal therapy (PTT) possesses desired therapeutic efficiency and insignificant side effects against cervical cancer. However, the lack of efficient and safe photothermal agents that operate in the second near-infrared (NIR-II) window is a main obstacle hindering the clinical transformation of PTT. Titanium dioxide (TiO2)-based nanomaterials are commonly applied in the biomedicine field, but the weak absorption and low photothermal conversion efficiency (PCE) of TiO2 in the NIR region limit their applications in PTT. Herein, we report the oxygen vacancy engineering that is a robust strategy to regulate the electronic structures of TiO2 for photothermal conversion properties optimizing. The obtained oxygen vacancy-doped TiO2−x nanosheets exhibit strong NIR-II absorption and high PCE owing to their decreased bandgap. Specifically, the PCE of TiO2−x nanosheets is determined to be 69.5 % in the efficient NIR-II window, which is much higher than that of widely reported PTT agents. Complete tumor recession without recurrence or pulmonary metastasis is realized by enhanced NIR-II PTT via TiO2−x nanosheets at an ultralow and safe laser exposure (0.6 W/cm2). Our findings suggest that oxygen vacancy engineering of nanomaterials could regulate their photothermal conversion performances, promoting the further application of TiO2-based nanomaterials in the biomedical.

Cover Feature: Boosting the Electrochemical Performance of Lithium‐Rich Cathodes by Oxygen Vacancy Engineering (Batteries & Supercaps 7/2023)

The Cover Feature shows the Li-rich layered oxide, as promising cathode materials for powering electric vehicle (EVs) applications due to their high energy density. Post-annealing strategy is developed to pre-introduce oxygen vacancies (OVs) into Li1.2Mn0.457Ni0.229Co0.114O2 cathode to modify the local Mn coordination environments, enhance structural stability, and suppress oxygen release. The presence of oxygen vacancies through thermal expansion diminishes the phase transitions in cathode materials during the heating process. More information can be found in the Research Article by H. Gao, G. Wang and co-workers.

Generation of Site-Selective Structural Vacancies in a Multinary Metal-Organic Framework for Enhanced Catalysis.

Generating structural vacancies in metal-organic frameworks (MOFs) by partially removing the inorganic and organic units from the scaffolds is an effective strategy to modulate the pore parameters of the extended structures. However, pore enlargement is accomplished at the cost of loss in the number of active sites in typical MOFs, since dissociations of coordination linkages to create vacancies are not site-selective. Here, we performed site-specific vacancy generation in a multinary MOF (FDM-6) by selectively hydrolyzing the weak Zn─carboxylate linkages and keeping the strong Cu─pyrazolate linkages untouched. Surface area and pore size range of the materials could be systematically tuned by adjusting the water content and hydrolysis time. More than 56% of the Zn(II) sites in FDM-6 could be vacant, as evidenced by the atom occupancy analysis using powder X-ray diffraction, while most of the redox-active Cu sites are held in the backbone. The vacancies create highly connected mesopores, thus guaranteeing facile transportation of the guest molecules toward the active sites. Compared with the pristine MOF, FDM-6 with site-selective vacancies shows enhanced catalytic activity in bulky aromatic alcohol oxidation. Overall, the multinary MOF provides a platform in which both pore size enhancement and full retainment of active sites could be delivered in one framework by simple vacancy engineering.

Facilitating Reconstruction of the Heterointerface Electronic Structure by the Enriched Oxygen Vacancy for the Oxygen Evolution Reaction

Exploring high-performance non-precious metal-based electrocatalysts for the sluggish oxygen evolution reaction (OER) process is fundamentally significant for the development of multifarious renewable energy conversion and storage systems. Oxygen vacancy (Vo) engineering is an effective leverage to boost the intrinsic activity of OER, but the underlying catalytic mechanism remains anfractuous. Herein, we realize the construction of oxygen vacancy-enriched porous NiO/ln2O3 nanofibers (designated as Vo-NiO/ln2O3@NFs hereafter) via a facile fabrication strategy for efficient oxygen evolution electrocatalysis. Theoretical calculations and experimental results uncover that, compared with the no-plasma engraving component, the presence of abundant oxygen vacancies in the Vo-NiO/ln2O3@NFs is conducive to modulating the electronic configuration of the catalyst, altering the adsorption of intermediates to reduce the OER overpotential and promote O* formation, upshifting the d band center of metal centers near the Fermi level (Ef), and also increasing the electrical conductivity and enhancing the OER reaction kinetics simultaneously. In situ Raman spectra proclaim that the oxygen vacancy can render the NiO/ln2O3 more easily reconstructible on the surface during the OER course. Therefore, the as-obtained Vo-NiO/ln2O3@NFs demonstrated distinguished OER activity, with an overpotential of only 230 mV at 10 mA cm-2 and excellent stability in alkaline medium, surmounting the majority of the previously reported representative non-noble metal-based candidates. The fundamental insights gained from this work can pave a new path for the electronic structure modulation of efficient, inexpensive OER catalysts via Vo engineering.

Ultrahigh concentration surface oxygen vacancies in ferrite foams for broadened electromagnetic absorption bandwidth

Currently, the absorbing bandwidth of the Ferrites is enormously limited at X-band and Ku-band by the poor intrinsic dielectric properties. Thus, there are few reports about the pure Ferrites’ application at 8-18 GHz. In this paper, the Ferrites composite foams (NFC) with a high surficial oxygen vacancy concentration (48.1%) were prepared by the NH4NO3 assisted solution-combustion strategy and solid phase sintering. Noteworthily, the concentration of surficial oxygen vacancy can be effectively regulated by the NH4NO3. This is facilitated to achieve balanced impedance matching. Therefore, the effective absorption bandwidth (EAB) of the NFC covered the whole X-band and Ku-band. Conduction loss and defect polarization relaxation realized by surficial oxygen vacancies were confirmed to be the key to such wide EAB for the NFC at 8-18 GHz. This work explores the important role of surficial oxygen vacancy engineering in regulating the dielectric parameters of the Ferrites, and provides a feasible strategy of surficial oxygen vacancy engineering for wide EAB electromagnetic performance at the high-frequency.

Defective core–shell NiCo2S4/MnO2 nanocomposites for high performance solid-state hybrid supercapacitors

The roles of oxygen vacancies to enhance the electrochemical performance were not clearly explained in comprehensive research. Herein, the vertically oriented NiCo2S4/MnO2 core–shell nanocomposites are in situ grown on the nickel foam (NF) surface and activated by oxygen vacancy engineering via a chemical reduction method. The scanning electron microscope (SEM) and transmission electron microscope (TEM) results show the shell-MnO2 is well coated on the core-NiCo2S4. The hierarchical core–shell nanostructures synergistically increase conductivity and provide rich faradaic redox chemical reactions. Moreover, the density functional theory (DFT) calculations further indicate that the electronic properties and structure properties in NiCo2S4/MnO2 electrode of reduction for 60 min (NiCo2S4/MnO2-60) are effectively adjusted by introducing oxygen vacancies. Impressively, the NiCo2S4/MnO2-60 electrode delivers substantially appreciable areal capacity of 2.13 mAh·cm−2 couple with superior rate capability. The as-prepared high-performance electrode material can assemble into solid-state hybrid supercapacitor. The fabricated NiCo2S4/MnO2-60//AC device exhibits an exceptional energy density of 43.16 Wh·kg−1 at a power density of 384.21 W·kg−1 and satisfactory cyclic stability of 92.1 % at current density of 10 mA·cm−2 after 10,000 cycles. In general, the work demonstrates the significance of NiCo2S4/MnO2-60 as a highly redox active electrode material for future practical application in supercapacitors.

Tracing the Effects of Nitrogen Doping and Sulfur Vacancy in Surging OER Electrocatalytic Activity of Bismuth Sulfide Nanorods

AbstractBismuth sulfide has become an attractive candidate in the electrocatalytic oxygen evolution reaction (OER), owing to its open coordination sites, unpaired electron orbitals, and mild electronegativity, but its OER performance is hindered by many deficiencies. The combination of heteroatom construction and vacancy engineering has been used to improve the OER performance of bismuth‐based electrocatalysts, but few studies can clearly describe the roles of dopants and vacancies in improving OER performance. Herein, N dopants and S vacancies in Bi2S3 nanorods via one‐step NH3/Ar plasma etching to investigate the enhanced OER performance are constructed. N dopants and S vacancies both regulated the intrinsic charge ordering of Bi2S3 nanorods, enhancing the p‐band center and Fermi level while also boosting the electroconductivity and wettability of the material. In addition, density functional theory calculations suggest that N doping promoted the adsorption of Bi sites, while S vacancies favored the desorption of S sites. Under the synergistic effects of N dopants and S vacancies, Bi2S3‐based electrocatalysts exhibited a low overpotential of 374 mV at 10 mA cm−2 and satisfactory durability, demonstrating a feasible strategy for exploiting main group element OER electrocatalysts.

Vacancy engineering in tungsten induced electronic structure optimization of MoSe2 for enhanced electrocatalytic hydrogen evolution reaction

Hydrogen (H2) is a clean and sustainable energy source, and it plays an integral part in lowering the world's reliance on fossil fuels. H2 evolution by the electrocatalytic reduction of water is a key step toward protecting the environment, and the development of cost-effective electrocatalysts is required for the production of huge quantities. In this article, metal (Tungsten)-doped molybdenum selenide (MoSe2) electrocatalysts for the hydrogen evolution process are proposed. MoSe2 activity in the hydrogen evolution process not only promotes the (selenium) Se vacancies and generation of phase shift from 2H to 1T but also optimizes the electronic structure of the material, which is favorable for hydrogen adsorption. Compared to pure P–MoSe2, engineered V–WMoSe2 nanosheets exhibit a low overpotential of ∼247 mV at a current density of 10 mA cm−2 and a lowered Tafel slope and decent turnover frequency (TOF). This technology not only explains the process behind the enhanced hydrogen evolution capabilities but also provides low-cost and effective Mo-based electrocatalysts by stimulating metal cations.

Electronic and Vacancy Engineering of Mo–RuCoOx Nanoarrays for High‐Efficiency Water Splitting

AbstractExploring efficient strategies to achieve novel high‐efficiency catalysts for water splitting is of great significance to develop hydrogen energy technology. Herein, unique molybdenum (Mo)‐doped ruthenium–cobalt oxide (Mo–RuCoOx) nanosheet arrays are prepared as a high‐performance bifunctional electrocatalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through combining electronic and vacancy engineering. Theoretical calculations and experimental results reveal that the incorporation of Ru and Mo can effectively tune the electronic structure, and the controllable Mo dissolution coupling with the oxygen vacancy generation during surface reconstruction is able to optimize the adsorption energy of hydrogen/oxygen intermediates, thus greatly accelerating the kinetics for both HER and OER. As a result, the Mo–RuCoOx nanoarrays exhibit remarkably low overpotentials of 41 and 156 mV at 10 mA cm−2 for HER and OER in 1 m KOH, respectively. Furthermore, the two‐electrode electrolyzer assembled by the Mo–RuCoOx nanoarrays requires a cell voltage as low as 1.457 V to achieve 10 mA cm−2 for alkaline overall water splitting. This work holds great promise to develop novel and highly active electrocatalysts for future energy conversion applications.

Surface Oxygen Vacancy Inducing Li‐Ion‐Conducting Percolation Network in Composite Solid Electrolytes for All‐Solid‐State Lithium‐Metal Batteries (Small 22/2023)

All-Solid-State Lithium-Metal Batteries In article number 2207223, Jeeyoung Yoo, Youn Sang Kim, and co-workers present an all-solid-state lithium-metal battery with composite solid electrolyte. Specifically, the oxygen vacancy-rich indium tin oxide (ITO) nanoparticles (green-colored) induce the Li-ion conducting percolation network (red-colored) at the ITO-poly(ethylene oxide) (PEO) interface. The oxygen vacancy enables fast movement of Li-ions in the interface network. This phenomenon suggests that the vacancy engineering of filler holds strong promise for developing advanced all-solid-state batteries.

Electrocatalytic conversion of methane to ethanol by ultrathin WO3 nanosheets: Oxygen vacancy engineering

Electrocatalytic conversion of CH4 into valuable liquid products is an attractive strategy for utilization of natural gas, however, it was still constrained by low product yields. Herein, ultrathin WO3 nanosheets with adequate oxygen vacancies (Ov) as robust electrocatalysts for highly efficient CH4 conversion to ethanol were synthesized. Using the optimized sample, the ultrahigh ethanol yield and selectivity of 125,090 μmol gcat−1 h−1 and 99.4% are achieved within 8 h at low potential of 1.2 V vs. RHE, both of which outperform the previous reports as we know. The corresponding ethanol Faradic efficiencies is 50.7%. In-situ Raman spectra and density functional theory calculation reveal that Ov effectively enable CH activation and CC coupling, and eventually promotes the electrocatalytic activity and ethanol selectivity for CH4 conversion. This work provides a constructive avenue for designing electrocatalysts with both high activity and selectivity to realize CH4 conversion.

Atomic vacancies-engineered ultrathin trimetallic nanozyme with anti-inflammation and antitumor performances for intestinal disease treatment

Colitis-associated colorectal cancer, which represents a highly aggressive subtypes of colorectal cancer, requires concurrent antitumor and anti-inflammation therapies in clinic. Herein, we successfully engineered Ru38Pd34Ni28 ultrathin trimetallic nanosheets (TMNSs) by introducing diverse transition metal atoms into the structure of RuPd nanosheets. Density functional theory (DFT) calculations reveal that the elaborate introduction of transition metal Ru and Ni facilitates the formation of Ru–O and Ni–O bonds on the surface of TMNSs for efficient reactive oxygen species (ROS) and reactive nitrogen species (RNS) scavenging, respectively. Moreover, the engineered abundant atomic vacancies on their surface conspicuously improve the performance in eliminating reactive oxygen and nitrogen species (RONS). The designed TMNSs act as a multi-metallic nanocatalyst with RONS elimination performance for chronic colitis treatment by relieving inflammation, as well as photothermal conversion capability for colon cancer therapy by inducing hyperthermia effect. Profiting from the excellent RONS scavenging activities, TMNSs can down-regulate the expression levels of the pro-inflammatory factors, thereby leading to prominent therapeutic efficacy against dextran sulfate sodium-induced colitis. Benefiting from the high photothermal performance, TMNSs cause significant suppression of CT-26 tumors without obvious recurrence. This work provides a distinct paradigm to design multi-metallic nanozymes for colon disease treatment by elaborate introduction of transition metal atoms and engineering of atomic vacancies.

Core-shell structure strategy and oxygen vacancy engineering of 0.1LaMnO3@0.9(Ba0.5Sr0.5)TiO3 ceramics towards tuning electrical properties

In recent years, core-shell structures have attracted much attention for their potential in tuning the functional properties of materials and have become an effective method for preparing high-performance materials. In this work, core-shell structured 0.1LaMnO3@0.9(Ba0.5Sr0.5)TiO3 nanoparticles were fabricated by sol-gel method and dense ceramics were prepared at different sintering temperatures. The phase composition, morphology, chemical state and electrical properties were systematically investigated. Structural analysis confirmed the formation of 0.1LaMnO3@0.9(Ba0.5Sr0.5)TiO3 core-shell nanostructures. The results show that the prepared samples exhibit typical negative temperature coefficient characteristics in the range of 50–1000 °C, which is derived from the effect of carrier pairs and oxygen vacancies on the electrical properties. This study provides new insights from structure to material into guiding the development and design of advanced thermistor materials for temperature sensing applications.