Bulk Oxygen Research Articles

Exposure history, petrology, and shock‐induced sulfidization reaction of Alatage Mountain 001 strewn field samples

AbstractSeveral hundred meteorites with a total mass of over 100 kg were collected as the Alatage Mountain (AM) strewn field located in the Kumtag desert, Xinjiang Province, China. Twelve AM meteorites were studied in this work. Petrography, mineralogy, bulk chemistry, bulk oxygen isotopic compositions, and light noble gas concentrations and isotopic compositions were determined for all or for a selection of the meteorites. The studied meteorites are L‐chondrites that suffered a very strong impact; impact melt veins and melt pockets are widely distributed. More than 50% of the troilite exists in the form of blebs and veins in olivine and pyroxene. Some of these meteorites are impact melt recrystallized rocks (e.g., AM 037). The strong impact caused the decomposition of troilite, which led in AM 034 to the sulfidization reaction of olivine. The metal in most meteorites is almost completely altered, and the troilite has been significantly oxidized. Weathering resulted in the depletion of Mg, Fe, Co, and Ni, and the enrichment of Sr, Ba, Pb, and U in these meteorites. The cosmic ray exposure (CRE) ages measured for these specimens range between 6.2 ± 1.9 Ma and 9.0 ± 2.7 Ma, depending on the cosmogenic nuclide used. The average CRE age is 7.6 ± 1.3 Ma. Both 4He and 40Ar gas retention ages indicate that the strong impact which caused the shock effects occurred about 320 Ma ago.

Oxygen exchange and bulk diffusivity of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ: Quantitative assessment of active cathode material for protonic ceramic fuel cells

The oxygen surface exchange and bulk diffusivity of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ were determined by electrical conductivity relaxation (ECR) in order to quantitively assess cathode performance for protonic ceramic fuel cells (PCFCs). The measurements were performed at 600 °C, following pO2-step changes between 80 ppm to pure oxygen. The apparent value of surface exchange coefficient (k) and diffusion coefficient D, indicates BaCo0.4Fe0.4Zr0.1Y0.1O3-δ is a good oxygen conductor. k was found to vary with pO2 and surface area while the chemical diffusion coefficient D remained invariant with pO2 and surface coating. The fitted kinetic parameters obtained from ECR with reduction process (high to low pO2) were compared with that of the oxidation process (low to high pO2). In the presence of H2O, oxygen exchange kinetics was suppressed because of the competitive adsorption relationship between oxygen and H2O. Single cell measurements employing single phase BaCo0.4Fe0.4Zr0.1Y0.1O3-δ cathode and an anode prepared by phase inversion tape casting in a configuration of 40 wt% BCZYSm13 + 60 wt% NiO | BCZYSm13 | BCFZY0.1 exhibited a power density of ~200 mW/cm2 at 600 °C.

Persistent and partially mobile oxygen vacancies in Li-rich layered oxides

Increasing the energy density of layered oxide battery electrodes is challenging as accessing high states of delithiation often triggers voltage degradation and oxygen release. Here we utilize transmission-based X-ray absorption spectromicroscopy and ptychography on mechanically cross-sectioned Li1.18–xNi0.21Mn0.53Co0.08O2–δ electrodes to quantitatively profile the oxygen deficiency over cycling at the nanoscale. The oxygen deficiency penetrates into the bulk of individual primary particles (~200 nm) and is well-described by oxygen vacancy diffusion. Using an array of characterization techniques, we demonstrate that, surprisingly, bulk oxygen vacancies that persist within the native layered phase are indeed responsible for the observed spectroscopic changes. We additionally show that the arrangement of primary particles within secondary particles (~5 μm) causes considerable heterogeneity in the extent of oxygen release between primary particles. Our work merges an ensemble of length-spanning characterization methods and informs promising approaches to mitigate the deleterious effects of oxygen release in lithium-ion battery electrodes. Oxygen release in Li-rich layered oxides is of both fundamental and practical interest in batteries, but a varied mechanistic understanding exists. Here the authors evaluate the extent of oxygen release over extended cycles and present a comprehensive picture of the phenomenon that unifies the current explanations.

Second wave of COVID-19 pandemic and the surge of mucormycosis: Lessons learnt and future preparedness: Indian Society of Anaesthesiologists (ISA National) Advisory and Position Statement.

Second wave of COVID-19 pandemic and the surge of mucormycosis: Lessons learnt and future preparedness: Indian Society of Anaesthesiologists (ISA National) Advisory and Position Statement.

Enhanced formaldehyde gas sensing performance of ternary CuBi2O4 oxides through oxygen vacancy manipulation and surface platinum decoration

Oxygen vacancy construction has been regarded as an effective method to enhance the sensing performance of the gas sensors. Herein, in this work, two CuBi2O4 composites with nanoflowers (CBOF) and nanospheres (CBOS) structures were synthesized with similar BET specific surface area, pore size distributions and exposed facets. However, a higher bulk oxygen vacancy concentration was found in the CBOS composites, bringing a higher carrier concentration and lower baseline resistance. As a consequence, the CBOS sensors exhibited better formaldehyde gas sensing performance (10.9–60 ppm gas) than that of the CBOF sensors (5.8). After treated in NaBH4 solutions, both composites exhibited enhanced surface adsorbed oxygen species and formaldehyde sensing response, owning to the generation of more surface oxygen vacancies to facilitate the surface adsorptions and redox reactions. After that, the Pt nanoparticles were decorated on the CBOS surface with a reduced method. The formaldehyde sensing response and selectivity were further enhanced due to the surface catalytic activity of the Pt nanoparticles. This work proves that CuBi2O4 composites can be an ideal sensing platform through oxygen vacancy construction and noble metal sensitization, and will facilitate the development of p-type ternary sensing materials.

Interface and defect engineering enable fast and high-efficiency Li extraction of metatitanic acid adsorbent

Considering the striking theoretical Lithium (Li) uptake capacity, environmental benignity and low cost, metatitanic acid (H2TiO3, abbreviated to HTO) is considered to be one of the most promising lithium ion sieve (LIS) adsorbent for liquid-phase Li extraction technology. However, the discouraging adsorption kinetics seriously hampers its industrial application. Herein, the traditional HTO-LIS is promoted by the combined strategies of pore-structure construction, surface heteroatom modification and alien Zn ion bulk doping, which ameliorates the surface characterization of the HTO adsorbent towards fast Li+ capturing from the solution, facilitating the activation and replacement of Li+ on the interface. Further, the oxygen bulk defect originated from Zn doping accelerates the Li+ transfer in solid-phase via the depressed diffusion energy barrier. The interfacial modification and defect engineering synergistically cooperate to extremely speed up the Li extraction process that the Li uptake rate of the optimized sample (PN-HZTO-0.04) increases to 457% compared to the pristine HTO-0 adsorbent. Remarkably, in the optimized Solid/Liquid ratio adsorption test, the adsorption efficiency of above 96% are achieved in 2 h, without obvious capacity degradation and Ti dissolution loss during adsorption/desorption cycles, representing excellent recycling ability.

Infrared furnace for in situ neutron single-crystal diffraction studies in controlled gas atmospheres at high temperatures

To understand oxygen diffusion mechanisms in non-stoichiometric oxides, the possibility to explore structural changes as a function of the oxygen partial pressure with temperature and related oxygen bulk stoichiometry is mandatory. This article reports on the realization of a high-temperature furnace, suitable for single-crystal neutron diffraction, working continuously at temperatures of up to 1000°C at different and adjustable partial gas pressures of up to 2 bar (1 bar = 100 kPa). This allows exploration of the phase diagrams of non-stoichiometric oxides under in situ conditions and controlled oxygen partial pressure. As a pilot study, the structural changes of Pr2NiO4+δ were explored at room temperature (δ ≃ 0.24) and at 900°C under 1 bar P(O2) (δ ≃ 0.13) as well as under secondary vacuum (approximately 10−5 mbar) conditions yielding a δ close to zero. The strong anharmonic displacements of the apical oxygen atoms along the [110] shallow diffusion pathway, which were previously observed at room temperature and 400°C, become more isotropic at 900°C. The study shows that the anisotropic oxygen displacements, here related to lattice instabilities, play a major role in understanding oxygen diffusion pathways and related activation energies at moderate temperatures. This also shows the importance of the availability of reaction cells for single-crystal neutron diffraction to explore the phase diagram and associated structural changes of non-stoichiometric oxygen ion conductors and respective diffusion mechanisms.

Analysis and outlook of mass transport in ultralow Pt loading proton exchange membrane fuel cells

<p indent=0mm>Proton exchange membrane fuel cells (PEMFCs) for automotive propulsions have been regarded as an ideal and the most promising alternative to replace fossil-fuel based internal combustion engines due to the high performance, high energy efficiency and zero-emission. However, the high cost has severely impeded the commercialization of PEMFCs, especially the high cost of Pt-based precious metal catalyst used for the cathode oxygen reduction reaction (ORR). It is critical to reducing the amount of Pt and thus decreasing the cost of fuel cell stacks, which would lead to numbers of new challenges. On the one hand, the reduction of Pt load could increase the oxygen transport resistance in cathode catalyst layers (CCLs). In fact, the oxygen transport resistance could be divided into several constituent parts, i.e., oxygen transport resistances in CCLs, gas diffusion layers (GDLs) and the flow channels, where the transport resistance in CCLs is much higher than other resistances. Further, CCLs are constructed as heterogeneous composites of ORR electrocatalysts, conductive polymer such as perfluorinated sulfonic acid (PFSA) ionomer as well as the pore space determined. Hence, the oxygen transport resistance in CCLs includes the bulk transport resistance caused by oxygen diffusion in the nanopore and the local transport resistance caused by oxygen permeation through the ultrathin ionomer film covering on the Pt surface. Local oxygen transport behavior could be divided into three processes: (1) Oxygen adsorption from gas phase into ionomer, (2) oxygen diffusion inside the ionomer, and (3) oxygen adsorption from the ionomer to Pt surfaces. As the Pt loading decreases, local oxygen transport resistance would increase significantly, thus leading to a dramatical performance degradation at high current density of fuel cells. In specific, the oxygen adsorption at gas/ionomer interface used to be considered as Henry’s adsorption. However, it is proved recently that this type of adsorption should be quasi-logarithmic, due to the finiteness of the adsorption site on ionomer surface. In addition, the bulk oxygen transport resistance depends on the porosity and pore size distribution inside the electrodes. We summarized plenty of experimental results of effective oxygen diffusivities reported by different research groups, and found that all the experimental values are obviously smaller than the calculated results based on the classical Bruggeman approximation. It is believed that the effective porosity plays a more important role relative to the geometrical porosity in the estimation of bulk oxygen transport resistance in PEMFCs. On the other hand, confining effect of the ultrathin ionomer film could weaken the separation of hydrophilic and hydrophobic phases and then cut down the pathway of proton migration. There are two proton conduction mechanisms in CCLs: Grotthuss hopping and vehicular mechanism. The proton conduction in CCLs could be affected by numerous factors, such as temperature, ionomer structure, thickness of ionomer film, as well as cation contaminants in the ionomer film. Both high oxygen transport resistance and low proton conduction in ultra-low Pt membrane electrode assemblies would damage the performance and the lifetime of PEMFCs. In this review, the bulk and local transport behavior, proton transport in CCLs, as well as the corresponding influence on fuel cell performance are systematically analyzed, and a series of coping strategies are presented.

Catalytic combustion behaviors of petroleum coke with hematite catalyst in a micro fluidized bed thermogravimetric analysis

Both conventional TGA and fluidized bed have some inherent limitations in the accurate measurement of gas–solid reaction. To characterize the gas–solid process under the fluidization state, a micro fluidized bed thermogravimetric analysis (MFB-TGA) was developed based on the real-time measurement with precision of 0.1 mg mass, 0.1°C temperature, and 0.01 kPa pressure. In this study, we preliminarily applied the MFB-TGA in evaluating catalytic combustion of petroleum coke with respect to deducing Fe2O3 catalytic mechanism, lattice oxygen migration pathway, and apparent combustion kinetics. The measurement stability of MFB-TGA was impacted by various factors, such as inhomogeneous temperature distribution and slight gas disturbance. Even char combustion heat could destabilize the weight signal by inducing vigorous particle collisions. The lightweight design and several structural optimizations were implemented to improve the MFB-TGA performance with the result of realizing smooth weight loss curves with 0.1 mg errors during the entire experiment. The experimental analysis revealed that the catalytic mechanism of hematite was identified as CO homogeneous catalysis. Hematite accelerated the char combustion rate by intensifying the driving force of bulk oxygen diffusion to the carbon surface. It served as an oxygen carrier, transferring lattice oxygen to oxidize carbon monoxide surrounding char particles. The apparent intrinsic kinetics of 33.73 kJ/mol was determined by the isothermal differential approach, which was lower than the published results measured in regular TGA. The zero-order model exhibited an excellent linear correlation in describing combustion behaviors based on a function fitting process. The MFB-TGA had the potential for extensive application by providing a reliable and straightforward method in characterizing gas–solid reactions under a fluidization state.

Understanding the surface adsorption and oxidation of cubic Cr0.5Al0.5N by first-principles calculations

Bulk and surface properties of oxygen in cubic c-Cr0.5Al0.5N were investigated through first-principles calculations based on density functional theory (DFT) in the present work. It was observed that the (001) surface of c-Cr0.5Al0.5N terminated with Cr-Al-N is energetically favorable. Calculations of oxygen adsorbed on the (001) surface show that O is bonding with Cr preferentially instead of Al due to the stronger Cr-O bond strength in comparison with that of Al-O. The difference charge density and electronic density of states indicate that the electrons shared between O and Cr and hybridization between the O-p and Cr-d orbitals contribute to the formation of strong Cr-O bonding on the surface. An oxidation mechanism is proposed, i.e. the Cr-O bond is first established, resulting in the formation of α-Cr2O3, and subsequent incorporation of α-Al2O3 promotes the formation of a mixed (Cr, Al)2O3 scale.

Medium-Entropy perovskites Sr(FeαTiβCoγMnζ)O3-δ as promising cathodes for intermediate temperature solid oxide fuel cell

Medium-entropy perovskites Sr(FeαTiβCoγMnζ)O3-δ (SFTCM) are investigated as potential cathodes for intermediate temperature solid oxide fuel cell (IT-SOFC). The effects of entropy on crystal structure, thermal expansion coefficients (TEC), electrical conductivity, oxygen surface exchange and bulk diffusion coefficients, electrochemical performance, and long-term stability of SFTCM are systematically investigated. High entropy facilitates the diffusion of oxygen ions but hinders the transmission of electrons. The SFTCM with higher entropy shows a lower TEC, displays suppressed strontium surface segregation, and delivers more stable polarization resistance. Although the catalytic activity towards oxygen reduction reaction was slightly reduced, the maximum power density of the LSGM-supported (250 μm) single cell with SrFe0.25Ti0.25Co0.25Mn0.25O3-δ cathode can still reach 0.85 W cm−2 at 800 °C. All these results suggest that the medium-entropy SFTCM perovskites can be promising cathodes materials for IT-SOFC.

Synthesis, properties, and activity of MoVTeNbO catalysts modified by zirconia-pillared clays in oxidative dehydrogenation of ethane

Abstract Composites comprising MoVTeNbO mixed oxide and zirconia-pillared montmorillonite clays (PilCs) were prepared. XRD and TEM with EDX studies confirmed the preservation of M1 MoVTeNbO phase in these composites responsible for high activity and selectivity in ethane oxidative dehydrogenation into ethylene. For composites with PilC content of 10 wt%, the best ethylene yield exceeding that of bulk MoVTeNbO oxide was demonstrated for clays with zirconia pillars doped with Ce and Al possessing the highest specific surface area. This is explained by optimized chemical interaction of these clays with MoVTeNbO mixed oxide improving its bulk oxygen mobility and reactivity by structure disordering while blocking surface sites responsible for combustion due to the stabilization of the reactive terminal oxygen species.

Oxygen Vacancy Enhanced Two-Dimensional Lithium Titanate for Ultrafast and Long-Life Bifunctional Lithium Storage

Boosting sufficient Li+ ion mobility in Li4Ti5O12 (LTO) is crucial for high-rate performance lithium storage. Here, an ultrafast charge storage oxygen vacancy two-dimensional (2D) LTO nanosheet was successfully fabricated through a one-pot hydrothermal method. The selectively doped Al3+ into octahedron Li+/Ti4+ 16d sites not only provide bulk oxygen vacancy and appropriate distorted TiO6 octahedra to facilitate Li+ ions diffusion, but also serve as a "pillar" to stabilize the Ti-O framework. The oxygen vacancy lowers Li+ ion diffusion energy barrier. Moreover, the 2D structure provides open diffusion channels for fast Li+ ion transport. As a result, the sample shows excellent electrochemical performance for bifunctional lithium storage. As a lithium-ion battery anode, the capacity retention reaches 112.8 mA h g-1 after 5000 cycles at 40 C with a fading rate of 0.288% per 100 cycles. Meanwhile, as a lithium-ion capacitor anode, it exhibits an excellent rate capacity of 120 mA h g-1 after 5000 cycles at 500 C with nearly 100% Coulombic efficiency. The produced LTO shows much higher rate capacity and longer lifetime than the reported LTO. Density functional theory calculations also demonstrate that oxygen vacancy can facilitate Li+ ion diffusion kinetics. The relationship between oxygen vacancy content and Li+ ions diffusion energy barrier in LTO is quantified. This work pioneers a defect engineering strategy for synthesized high-performance electrode materials.

Predominance of Subsurface and Bulk Oxygen Vacancies in Reduced Manganese Oxide

Oxygen vacancies (Vos) play a vital role in the physical and chemical properties of oxide materials and their applications. Because Vos are first produced on oxide surfaces, it has been often recognized that they are richer at the top surface than at the subsurface or bulk region. Here the depth distribution of Vos in reduced manganese oxide (MnOx) films has been studied by a combination of ion-sputtering treatment and variable-angle X-ray photoelectron spectroscopy measurement. The density of Vos on the top surface is determined to be ∼8% lower than that in the subsurface region after reduction treatment of the oxide in CO at 573 K. Density functional theory calculations show that lattice oxygen atoms in the bulk tend to migrate and fill into the Vos on the top surface with a barrier of 0.94 eV at most. The stability of Vos in the bulk is higher than that on the surface via a reduced Mn3O4 skeleton, which can be reflected by the energy of oxygen filling at the Vo.

HCHO Catalytic Oxidation Performance over Cerium Containing MCM-41 Type Mesoporous Materials Supported Ag Catalysts

Understanding the effects of cerium in the formaldehyde (HCHO) catalytic oxidation performance over Ag/MCM-41 catalysts, cerium modified MCM-41 mesoporous materials (Ce-MCM-41) with different ratios were synthesized by one-step hydrothermal method. The activity test results showed that Ag/Ce-MCM-41 with the ratio of Si:Ce = 1:1 catalysts could reach complete HCHO oxidation above 130 °C. These Ag/Ce-MCM-41 catalysts with different Si:Ce ratios were characterized by IR, SXRD, XRD, TEM, UV–Vis, Raman, XPS and H2-TPR. The results show that the interactions between Ag and Ce, between Ce and SiO2 in our Ag/Ce-MCM-41 are enhanced due to adding Ce to MCM-41. The presence of Ce-SiO2 interaction dramatically enhances the reducibility of surface-capping oxygen of CeO2, promotes the bulk oxygen migration to the surface and creates oxygen vacancies in the bulk region of CeO2 and the presence of more oxygen vacancies can facilitate the anchoring and dispersing of Ag particles, which lastly improves the interaction between Ag and Ce. In addition, the amount of formed oxygen vacancy is the highest when the Si:Ce = 1:1. The activation of surface oxygen is closely related to oxygen vacancy, O2 may be transformed into the highly active O2−. The high active O2− in surface adsorbed oxygen promotes the activation of oxygen molecules and enhanced the catalytic oxidation of HCHO.

The composition and redox state of bridgmanite in the lower mantle as a function of oxygen fugacity

The chemistry of bridgmanite (Brg), especially the oxidation state of iron, is important for understanding the physical and chemical properties, as well as putting constraints on the redox state, of the Earth’s lower mantle. To investigate the controls on the chemistry of Brg, the Fe3+ content of Brg was investigated experimentally as a function of composition and oxygen fugacity (fo2) at 25 GPa. The Fe3+/∑Fe ratio of Brg increases with Brg Al content and fo2 and decreases with increasing total Fe content and with temperature. The dependence of the Fe3+/∑Fe ratio on fo2 becomes less steep with increasing Al content. Thermodynamic models were calibrated to describe Brg and ferropericlase (Fp) compositions as well as the inter-site partitioning of trivalent cations in Brg in the Al–Mg–Si–O, Fe–Mg–Si–O and Fe–Al–Mg–Si–O systems. These models are based on equilibria involving Brg components where the equilibrium thermodynamic properties are the main adjustable parameters that are fit to the experimental data. The models reproduce the experimental data over wide ranges of fo2 with a relatively small number of adjustable terms. Mineral compositions for plausible mantle bulk compositions can be calculated from the models as a function of fo2 and can be extrapolated to higher pressures using data on the partial molar volumes of the Brg components. The results show that the exchange of Mg and total Fe (i.e., ferric and ferrous) between Brg and Fp is strongly fo2 dependent, which allows the results of previous studies to be reinterpreted. For a pyrolite bulk composition with an upper mantle bulk oxygen content, the fo2 at the top of the lower mantle is −0.86 log units below the iron–wüstite buffer (IW) with a Brg Fe3+/∑Fe ratio of 0.50 and a bulk rock ratio of 0.28. This requires the formation of 0.7 wt.% Fe–Ni alloy to balance the raised Brg ferric iron content. With increasing pressure, the model predicts a gradual increase in the Fe3+/∑Fe ratio in Brg in contrast to several previous studies, which levels off by 50 GPa. Oxygen vacancies in Brg decrease to practically zero by 40 GPa, potentially influencing elasticity, diffusivity and rheology in the top portion of the lower mantle. The models are also used to explore the fo2 recorded by inclusions in diamonds, which likely crystallized as Brg in the lower mantle, revealing oxygen fugacities which likely preclude the formation of some diamonds directly from carbonates, at least at the top of the lower mantle.

The difference of PMMA‐brush‐modification on the oxygen permeable perovskite‐type oxides by consisting elements

AbstractOxygen permeation of perovskite‐type ceramics consists of three elementary processes: oxygen absorption, bulk oxygen diffusion, and oxygen desorption. In most cases, the rate‐determining step is the oxygen diffusion step, and the use of thin films improves the oxygen permeation rate of perovskite‐type ceramics. Polymer‐brush‐modification is a useful technique to produce thin films. Grafted PMMA‐brushes exhibit a screening effect for attractive interactions between core ceramic particles, thereby inducing repulsive forces on them. This results in the formation of a densely packed ordered array. Modification of the polymerization‐initiator and polymer‐brushes should affect the oxygen permeation properties of the ceramic particles, especially surface oxygen adsorption and desorption. In this paper, it is demonstrated that these modifications change the cation chemical states and lower the oxygen desorption rate, while increasing the desorption peak temperature. The surface of La–Sr–Co–Fe perovskite‐type oxides was modified only with the polymerization initiator, (2‐bromo‐2‐methyl)propionyloxyhexyltriethoxysilane (BHE) because there is no direct interaction between the polymer‐brush and the substrate, while the initiator is directly modified to the substrate. The oxygen desorption behavior of BHE‐modified oxides indicates that its oxygen desorption property is impeded without modification with PMMA. The investigation of BHE‐modified oxide cation chemical states and oxygen desorption behaviors imply that the BHE‐modifying site and change in chemical states have selectivity depending on cation species. Although sintering causes the formation of silicate and ceramic decomposition, this step can eliminate the harmful effects of BHE‐modification in total. When conventional La–Sr–Co–Fe perovskite‐type ceramics are used, sintering is preferable for the recovery of thin‐film surface reactions. However, if we utilize site selectivity of BHE‐modification, the harmful effects of those modifications can be avoided by modifying BHE onto sites that hardly participate in surface reactions.

Rich bulk oxygen Vacancies-Engineered MnO2 with enhanced charge transfer kinetics for supercapacitor

Rich bulk oxygen vacancies can enhance electrical conductivity and promote electron transfer. Local electric-field formed around oxygen vacancies can accelerate Na + transfer rate in bulk MnO 2 , and induce a decreased Na + diffusion energy barrier. Both of the enhanced electron and Na + transfer kinetics can ameliorate energy storage performance of MnO 2 . • Rich bulk oxygen vacancy is achieved by complex induced chemical precipitation. • Enhanced electrical conductivity of MnO 2 -C is obtained. • Robust local electric-field ameliorates the charge transfer kinetics. Transition metal oxides with high theoretical capacity are known to show greatly limited energy and power density of electrochemical energy storage due to its sluggish charge transfer kinetics. Although oxygen vacancies at atomic level can efficiently regulate electronic configuration and ameliorate electrochemical performance, the construction of rich bulk oxygen vacancies is still a challenge. Here, rich oxygen vacancies were successfully introduced in bulk MnO 2 through complex induced chemical precipitation. Enhanced electrical conductivity and local electric-field formed around oxygen vacancies promote the charge transfer, remarkably enhancing capacitance and rate capability. Asymmetric supercapacitor of MnO 2 with rich bulk oxygen vacancies exhibits high energy density (54.2 Wh kg −1 ) and power density (3279.6 W kg −1 ), superior to most reported MnO 2 -based supercapacitor. Our strategy paves a way for the fine regulation of bulk electronic configuration and reaction kinetics.

Cycling mechanism of Li2MnO3: Li–CO2 batteries and commonality on oxygen redox in cathode materials

Summary Li2MnO3 has been considered to be a representative Li-rich compound with active debates on oxygen activities. Here, by evaluating the Mn and O states in the bulk and on the surface of Li2MnO3, we clarify that Mn(III/IV) redox dominates the reversible bulk redox in Li2MnO3, while the initial charge plateau is from surface reactions with oxygen release and carbonate decomposition. No lattice oxygen redox is involved at any electrochemical stage. The carbonate formation and decomposition indicate the catalytic property of the Li2MnO3 surface, which inspires Li-CO2/air batteries with Li2MnO3 acting as a superior electrocatalyst. The absence of lattice oxygen redox in Li2MnO3 questions the origin of the oxygen redox in Li-rich compounds, which is found to be of the same nature as that in conventional materials based on spectroscopic comparisons. These findings provide guidelines on understanding and controlling oxygen activities toward high-energy cathodes and suggest opportunities on using alkali-rich materials for catalytic reactions.

Tailoring bulk Li+ ion diffusion kinetics and surface lattice oxygen activity for high-performance lithium-rich manganese-based layered oxides

Lithium-rich manganese-based layered oxides (LRMOs) offer joint cationic and anionic redox at a high voltage, thus promising high energy density for lithium-ion batteries (LIBs). However, the restive anion redox is also connected with poor rate performance, severe capacity fading, and continuous voltage decay. Herein, a successful strategy for enhancing the Li+ ion diffusivity and structure stability of LRMOs is proposed. The obtained material possesses high cationic and anionic redox activity due to the introduction of Te6+. Moreover, a heterogeneous protective layer that is composed of acid-resistant Mg3(PO4)2 and self-induced cation-disordered phase with passivated lattice oxygen is verified to be located on the surface of the material, thereby restraining the structural degeneration. Benefitting from the unique architecture, the modified material presents a favorable cycling performance and excellent rate capability (178.8 mA h g-1, 10 C). More importantly, the voltage decay is significantly suppressed during cycling. The finding here exhibits the importance of activating cationic and anionic redox in the bulk and passivating surface oxygen for enhancing reversible capacity at high rates and improving structural stability, providing a ponderable way to promote the electrochemical performance of LRMOs.