Coexistence Of Oxygen Vacancies Research Articles

In Situ Immobilizing Atomically Dispersed Ru on Oxygen-Defective Co3O4 for Efficient Oxygen Evolution

The synergistic regulation of the electronic structures of transition-metal oxide-based catalysts via oxygen vacancy defects and single-atom doping is efficient to boost their oxygen evolution reaction (OER) performance, which remains challenging due to complex synthetic procedures. Herein, a facile defect-induced in situ single-atom deposition strategy is developed to anchor atomically dispersed Ru single-atom onto oxygen vacancy-rich cobalt oxides (Ru/Co3O4–x) based on the spontaneous redox reaction between Ru3+ ions and nonstoichiometric Co3O4–x. Accordingly, the as-prepared Ru/Co3O4–x electrocatalyst with the coexistence of oxygen vacancies and Ru atoms exhibits excellent performances toward OER with a low overpotential of 280 mV at 10 mA cm–2, a small Tafel slope value of 86.9 mV dec–1, and good long-term stability in alkaline media. Furthermore, density functional theory calculations uncover that oxygen vacancy and atomically dispersed Ru could synergistically tailor electron decentralization and d-band center of Co atoms, further optimizing the adsorption of oxygen-based intermediates (*OH, *O, and *OOH) and reducing the reaction barriers of OER. This work proposes an available strategy for constructing electrocatalysts with abundant oxygen vacancies and atomically dispersed noble metal and presents a deep understanding of synergistic electronic engineering of transition-metal-based catalysts to boost oxygen evolution.

Macro/Mesoporous Carbon/Defective TiO2 Composite as a Functional Host for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) hold great potential as next-generation electrochemical energy storage and conversion systems owing to their higher theoretical capacity (1675 mAh/g). However, the shuttling of soluble polysulfides with slow redox reaction kinetics has restricted the commercialization of LSBs. The design and synthesis of effective cathode hosts provide a promising solution to improving the electrochemical performances of LSBs. Herein, we report a composite of macro/mesoporous carbon (MMC) coupled with defective TiO2 nanoparticles as a novel functional cathode host for LSBs. The MMC/TiO2 composite has been synthesized using a template-based approach combining simple hydrothermal reactions. Experimental characterizations, electrochemical measurements, and first-principles density functional theory (DFT) calculations disclose that the combination of macro/mesoporous carbon and defective TiO2 (coexistence of oxygen vacancies and Ti3+) effectively suppresses the undesired polysulfide shuttling effect and promotes fast redox conversion of polysulfides during cycling. The resultant LSBs with MMC/TiO2@S as a composite cathode thus exhibit impressive electrochemical properties with high capacity (1420 mAh/g at 0.2C), good rate capability (522 mAh/g at 2C), and cycling ability (65.6% retention at 0.2C over 60 cycles). This work can present some new insights into the rational design and exploration of novel material systems and compositions for applications in LSBs.

First-Principles Insight into the Effects of Intrinsic Oxygen Defects on Proton Conduction in Ruddlesden-Popper Oxides.

Understanding proton transport in Ruddlesden-Popper (RP) oxides, as attractive electrode materials for protonic ceramic fuel cells, is challenging because of the complexity of intrinsic oxygen defects in first-series RP oxides (A2BO4). We investigated the processes of intrinsic oxygen defects in proton transportation, such as formation of defects, incorporation of dissociative water into the defective lattice, transfer of a proton along the oxygen sites, and electronic properties of the transition state (TS) in A2BO4. The coexistence of oxygen vacancies (VO) and interstitial oxygen (Oi), VO+Oi defect pair, presents advantageous hydration energies and lattice distortions efficiently accelerating proton transport in the lattice. Moreover, the inherent driving force for proton transport is related to the O 2p band level by O-H···O bond interactions in the TS. Our findings elucidate the fundamental mechanism of proton conduction affected by intrinsic oxygen defects, which will motivate the community to focus more on defect engineering to enhance performance.

TiO2-x/CoOx photocatalyst sparkles in photothermocatalytic reduction of CO2 with H2O steam

Solar photocatalytic production of fuels from CO2 and H2O remains a challenging goal. Herein we report a strategy to co-modify TiO2 with oxygen vacancies and CoOx nanoclusters for enhanced photothermocatalytic reduction of CO2. The TiO2-x/CoOx material exhibits prominently enhanced activity for the yield of CH4 and CO under ultraviolet irradiation at elevated temperature of 393 K, which is 111.3- and 13.2-times greater yield of CH4 and CO, respectively than the conventional photocatalytic process at 298 K, and 175.1- and 2.9-times greater yield of CH4 and CO, respectively than the pristine TiO2 under the same photothermocatalytic conditions. Control experiments over singly modified TiO2 and doubly modified TiO2 by different preparation history, together with high-resolution transmission electron microscope (HRTEM), electron spin resonance (ESR), and transient photovoltage measurements reveal the synergistic effect of oxygen vacancies and surface-grafted CoOx on the photothermocatalytic reduction of CO2 to CH4, i.e. oxygen vacancies at TiO2 surface facilitate the adsorption and reduction of CO2 and the dispersion of CoOx nanoclusters, whereas surface-grafted CoOx clusters facilitate the hole trapping and the oxidation of H2O. Thereby the coexistence of oxygen vacancies and CoOx nanoclusters at TiO2 surface promote the separation of photogenerated electrons and holes, and remarkably enhance the eight-electron reduction of CO2 to CH4 under photothermocatalytic conditions. This study shows the great potential of photo-thermal synergy on CO2 reduction and provides a promising means to design photothermocatalysts for solar photocatalytic reduction of CO2 to fuel.

Synergetic Catalysis of Nickel Oxides with Oxygen Vacancies and Nickel Phosphide for the Highly Efficient Hydrodeoxygenation of Phenolic Compounds

AbstractThe highly efficient hydrodeoxygenation of oxygenated chemicals at a low temperature is a critical issue for biomass crude oil upgrading to reduce equipment and operation expense. The unique electronic features of oxygen vacancies have been found to facilitate deoxygenation above 250 °C. In this work, a series of NiOx/SiO2 catalysts that contain oxygen vacancies was prepared by a sol–gel and controllable temperature‐programmed reduction method. Results show that NiOx/SiO2 has a superior phenol hydrogenation activity in deoxygenation even at 180 °C to Ni2P/SiO2. The high hydrogenation activity derives from the flat adsorption of phenolics over low‐valence Ni cations induced by connected oxygen vacancies. After the introduction of NiOx into Ni2P catalysts, composite NiOx‐Ni2P/SiO2 (0.43≤x<1) bifunctional catalysts demonstrate better phenol hydrodeoxygenation performances under mild reaction conditions in comparison with individual Ni2P and NiOx catalysts and most catalysts presented previously because the coexistence of oxygen vacancies from NiOx and the acidity induced by Ni2P results in the synergistic effect of the adsorption configuration and hydrodeoxygenation ability. Besides, this composite catalyst also has a high activity for the hydrodeoxygenation of different bio‐derived cresol isomers. The reuse test results confirm that oxygen vacancies are relatively stable in comparison with the phosphide.

High-k-rare-earth-oxide Eu2O3 films for transparent resistive random access memory (RRAM) devices

Fully transparent indium–tin-oxide/high-k-rare-earth-oxide Eu2O3/F-doped SnO2 devices that show stable bipolar resistance switching have been successfully fabricated. In addition to the transmittance of above 86% for visible light, high resistance ratio, good data retention and initial forming-free resistance switching behaviour were obtained in the transparent memory. The results of high-resolution spectroscopy and x-ray photoelectron spectroscopy analyses combining with the temperature dependence of resistance suggest that metallic Eu filaments are formed in the low-resistance state. Mechanism analysis indicates that the coexistence of oxygen vacancies and metallic Eu in the Eu2O3 films plays an important role in the forming-free resistive switching performance. The switching mechanism was attributed to formation/oxidation of filamentary and oxygen ion migration.

Influence of defects on magnetism of Co-doped ZnO

Two kinds of Zn0.97Co0.03O powders were prepared by precursor thermal decomposition under different conditions. One grown at low temperature has a positive Curie–Weiss temperature Θ, while the other grown at high temperature has a negative Θ. Both of them contain oxygen vacancies. There are more shallow donors in the former than those in the latter. It is proposed that coexistence of oxygen vacancies and shallow donors is necessary to induce ferromagnetic coupling between Co ions.