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Over the last few years, keen interest has been taken in creating and tuning the concentration of oxygen vacancies in electrode materials to enhance their performance and to develop next-generation rechargeable batteries. Oxygen vacancies can be created in electrode materials by using various synthesis techniques. Furthermore, controlled generation of oxygen vacancies in electrode materials plays an essential role in enhancing their electrochemical properties. However, controlled creation of oxygen vacancies in electrode materials via facile techniques is still a challenge. Furthermore, the characterization techniques available to quantify the exact amount and type of oxygen vacancies present in the bulk as well as the surface of a material are not appropriate. Hence, in this review, we have comprehensively summarized the recent reports on oxygen vacancy-based electrode materials and their impact on the electrochemical performance of rechargeable batteries. Furthermore, the challenges and prospects of these oxygen vacancy-rich electrode materials are also discussed.

In recent years, oxygen vacancy (VO) engineering has become a research hotspot in the field of photocatalysis. Herein, an efficient GQDs/BiOCl-VO heterojunction photocatalyst was fabricated by loading graphene quantum dots (GQDs) onto BiOCl nanosheets containing oxygen vacancies. ESR and XPS characterizations confirmed the formation of oxygen vacancy. Combining experimental analysis and DFT calculations, it was found that oxygen vacancy promoted the chemical adsorption of O2, while GQDs accelerated electron transfer. Benefiting from the synergistic effect of oxygen vacancy, GQDs, and dye sensitization, the as-prepared GQDs/BiOCl-VO sample exhibited improved efficiency for RhB degradation under visible-light irradiation. A 2 wt% GQDs/BiOCl-VO composite effectively degraded 98% of RhB within 20 min. The main active species were proven to be hole (h+) and superoxide radical (·O2−) via ESR analysis and radical trapping experiments. This study provided new insights into the effective removal of organic pollutants from water by combining defect engineering and quantum dot doping techniques in heterojunction catalysts.

Denitrification catalysts are essential for reducing NOx emissions from combustion and protecting air quality. This study introduces and validates an Oxygen Vacancy Index (OVI) that quantifies redox-active vacancies and guides defect engineering in fly ash-derived catalysts. We apply a simple cascade strategy to tune defect types; procedural details are reported in Methods rather than in the abstract. The optimized catalyst shows an over-twofold increase in OVI compared with raw fly ash. Surface-related changes and point/line defects contribute comparably (≈one-third each) to the explained variance. OVI positively correlates with NO conversion, and the optimized material delivers high NO conversion at 400 °C. These results establish a quantitative process–structure–performance link. Looking ahead, the OVI framework can guide defect design in other waste-derived catalysts and support scale-up to monolith coatings and pilot-scale units. This OVI-guided route provides a simple, low-cost path to robust fly ash catalysts for industrial NOx control.

Valence state engineering has emerged as a powerful strategy to optimize catalytic performance by modulating the electronic structure of metal active sites. However, the valence state regulation in high‐entropy compounds (HECs) remains elusive due to their complex multi‐element components and electronic interactions. Here, the valence states of different metals in two‐dimensional (2D) high entropy oxide (HEO) (FeNiMoRuV)O2−x are precisely modulated through controlled pyrolysis of corresponding 2D high entropy hydroxide (HEHO) (FeNiMoRuV)(OH)2 under varying temperatures. Temperature‐controlled pyrolysis selectively reduces the oxidation state of Ru, while simultaneously increasing the valence state of other constituent metals (Fe, Ni, Mo, and V), suggesting a competitive redox equilibrium. Notably, these low‐valence Ru sites with oxygen vacancy in 2D HEO significantly reduce Ru–O bond energy and promote the generation of O–*O intermediates, thereby enabling oxygen evolution with a lattice oxygen mediated‐oxygen vacancy site mechanism. 2D HEO with low‐valence Ru exhibits superior electrolytic water performance (HER/OER) compared to HEHO and other HEO with high‐valence Ru, achieving a current density of 1000 mA cm−2 at 1.923 V, which exceeds the commercial Pt/C||RuO2 system. Therefore, this study reveals the valence state regulatory mechanism of HECs and provides a solid hammer for the catalytic mechanism of valence state engineering. The competitive redox equilibrium among different elements in 2D HEO is regulated through temperature‐controlled pyrolysis of 2D HEHO, obtaining 2D HEO with a continuously adjustable valence state of Fe, Ni, Mo, Ru, and V elements, which modulate the strength of the metal–O bond and activate the LOM‐OVSM for OER.

Recently, HfO2‐based ferroelectric thin films have attracted widespread interest in developing next‐generation nonvolatile memories. To form a metastable ferroelectric orthorhombic phase in HfO2, a post‐annealing process is typically necessary. However, the microscopic mechanism underlying the effect of annealing temperature on ferroelectric domain nucleation and growth is still obscure, despite its importance in optimizing the operation speed of HfO2‐based devices. In this study, the ferroelectric properties and polarization switching of Hf0.5Zr0.5O2 thin films annealed at different temperatures (550–700 °C) are systematically investigated. Evidently, the crystal structure, remnant polarization, and dielectric constant monotonically change with annealing temperature. However, microscopic piezoresponse force microscopy images as well as macroscopic switching current measurements reveal non‐monotonic changes in the polarization switching speed with annealing temperature. This intriguing behavior is ascribed to the difference in the ferroelectric‐domain nucleation process induced by the amount of oxygen vacancies in the Hf0.5Zr0.5O2 thin films annealed at different temperatures. This work demonstrates that controlling the defect concentration of ferroelectric HfO2 by tuning the post‐annealing process is critical for optimizing device performance, particularly polarization switching speed. The ferroelectric properties and polarization switching of Hf0.5Zr0.5O2 thin films annealed at various temperatures are systematically investigated. Piezoresponse force microscopy, as well as switching current measurements, revealed non‐monotonic changes in the polarization switching speed concerning the annealing temperature. These variations are attributed to differences in the ferroelectric‐domain nucleation process induced by different defect levels in the films.

Five different (commercial and self-synthesized) titania samples were mixed with NaBH4 and then heated to obtain black titania samples. The change in synthesis conditions resulted in the preparation of nine different photocatalysts, most of which were black in color. The photocatalysts were characterized by various methods, including X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), photoacoustic and reverse-double beam photoacoustic spectroscopy (PAS/RDB-PAS). The photocatalytic activity was tested for oxidative decomposition of acetic acid, methanol dehydrogenation, phenol degradation and bacteria inactivation (Escherichia coli) under different conditions, i.e., irradiation with UV, vis, and NIR, and in the dark. It was found that the properties of the obtained samples depended on the features of the original titania materials. A shift in XRD peaks was observed only in the case of the commercial titania samples, indicating self-doping, whereas faceted anatase samples (self-synthesized) showed high resistance towards bulk modification. Independent of the type and degree of modification, all modified samples exhibited much worse activity under UV irradiation than original titania photocatalysts both under aerobic and anaerobic conditions. It is proposed that the strong reduction conditions during the samples’ preparation resulted in the partial destruction of the titania surface, as evidenced by both microscopic observation and crystallographic data (an increase in amorphous content), and thus the formation of deep electron traps (bulk defects as oxygen vacancies) increasing the charge carriers’ recombination. Under vis irradiation, a slight increase in photocatalytic performance (phenol degradation) was obtained for only four samples, while two samples also exhibited slight activity under NIR. In the case of bacteria inactivation, some modified samples exhibited higher activity under both vis and NIR than respective pristine titania, which could be useful for disinfection, cancer treatment and other purposes. However, considering the overall performance of the black titania samples in this study, it is difficult to recommend them for broad environmental applications.

Rapid recombination of photogenerated carriers severely limits the photocatalytic performance of conventional semiconductor photocatalysts, while conventional heterojunctions generally suffer from inefficient charge separation and sluggish interfacial kinetics due to poor lattice matching and unidirectional recombination. Herein, we break through these limitations by constructing an oxygen vacancies (OVs)‐mediated S‐scheme via covalent bridging between a metal–organic framework (MOF) and a covalent organic framework (COF), coupled with vacuum‐induced OVs engineering. This novel architecture not only preserves the strong redox potentials of the constituent materials but also introduces dual‐channel charge transport pathways significantly enhancing carrier separation. Femtosecond transient absorption spectroscopy (fs‐TAS) reveals that the OVs‐induced trap states extend the carrier lifetime to 278 ps—2.5 times longer than the parent materials. The optimized catalyst achieves exceptional removal efficiencies for multiple heavy metal ions (Cu⁺, ReO4−, MoO42−, MnO4−, Cr2O72−, and UO22⁺), with UO22⁺ removal rates 8.8 and 17.1 times higher than those of the pristine MOF and COF, respectively. This work presents a universal “defect‐mediated dual transport” strategy, offering new insights into solar‐driven environmental purification and energy conversion. Covalent bond MOF/COF S‐scheme which generated via vacuum‐induced oxygen vacancies are report. OVs at the interface can trigger a dual‐channel charge transport mechanism, significantly enhancing catalytic performance. This work not only designs a high‐performance photocatalysts for environmental remediation, but also induces a new concept of “defect engineering for charge transport optimization”, providing a groundbreaking approach to controlling charge dynamics in next generation photocatalytic systems.

The introduction of oxygen vacancies (OVs) is a promising strategy to enhance the hydrogen (H2) evolution efficiency of photocatalysts. Sodium borohydride (NaBH4) is widely used as a reducing agent to introduce OVs, particularly in composite materials. However, its impact on H2 evolution remains underexplored. In this study, by employing various mass ratios of NaBH4 to P/Ag/Ag2O/Ag3PO4/TiO2 (PAgT), OVs modified PAgT (R-PAgT) composites, which were synthesized and systematically characterized by XRD, FT-IR, and XPS. R-PAgT-10 with an optimal mass ratio exhibited a superior H2 evolution efficiency and stability, maintaining its performance over 20 cycles under visible light irradiation, while the higher mass ratio of NaBH4/PAgT led to the disruption of the crystal structure with excessive OVs amounts, resulting in poor stability. This study highlighted the importance of utilizing the optimal mass ratio of NaBH4 to prepare OVs-PAgT for successful and stable H2 evolution under visible light irradiation, which holds promise for developing efficient and durable photocatalysts for renewable energy applications.

Modifying electrocatalysts nanostructures and tuning their electronic properties through defects-oriented synthetic strategies are essential to improve the oxygen evolution reaction (OER) performance of electrocatalysts. Current synthetic strategies about electrocatalysts mainly target the single or double structural defects, while the researches about the synergistic effect of multiple structural defects are rare. In this work, the ultrathin NiFe layered double hydroxide nanosheets with a holey structure, oxygen vacancies and Ni 3+ defects on nickel foam (NiFe-LDH-NSs/NF) are prepared by employing a simple and green H 2 O 2 -assisted etching method. The synergistic effect of the above three defects leads to the exposure of more active sites and significant improvement of the intrinsic activity. The optimized catalyst exhibits an excellent OER performance with an extraordinarily low overpotential of 170 mV at 10 mA·cm −2 and a small Tafel slope of 39.3 mV·dec −1 in 1 M KOH solution. Density functional theory calculations reveal this OER performance arises from pseudo re-oxidized metal-stable Ni 3+ near oxygen vacancies (O vac ), which suppresses 3d-e g of Ni-site and elevates d-band center towards the competitively low electron-transfer barrier. This work provides a new insight to fabricate advanced electrocatalysts for renewable energy conversion technologies.