Bulk Oxygen Research Articles

Titanium Oxide Electrocatalytic Membrane Filtration: "Two Faces" of Oxygen Vacancies in Generation and Transformation of Reactive Oxygen Species.

Oxygen vacancies are crucial to the production of reactive oxygen species (ROS) in the metal oxide electrocatalytic membrane (MOx EM) process. Here, using cathodic TiOx EM as a model, we thoroughly reveal the roles of oxygen vacancies in ROS generation and transformation. Oxygen vacancies significantly promote H2O2 and •OH production at low concentrations (increment <35%) but inhibit their production at high concentrations (increment >35%). Electrochemical analysis discloses that the enhancement of ROS production profits from the acceleration of charge transfer kinetics by both bulk and surface oxygen vacancies, whereas we attribute the decline in ROS production to the strong adsorption of ROS by surface oxygen vacancies. It is strongly supported by theoretical calculations that reveal the promoted adsorption of *OOH and *OH by oxygen vacancies, which intensifies the capture and scavenging of H2O2 and •OH. Moreover, the gradual increase of interaction time between ROS and oxygen vacancies (from ∼1 to ∼5 s) notably reduces the generation and transformation efficiency of ROS, further highlighting the detrimental impact of oxygen vacancies. In summary, oxygen vacancies show "two faces" toward ROS generation and transformation, acting as ROS promoters at low concentrations but inhibitors at high concentrations. A medium oxygen vacancy concentration is preferred for ROS production, thus causing impressive pollutant removal (>95% removal of bisphenol A within 1.2-1.5 s at 360-440 LMH). This study provides guidance on regulating ROS generation and transformation by manipulating the oxygen vacancy concentration to enhance the decontamination efficiency of MOx EMs.

Lattice oxygen migration of iron-based oxygen carrier during chemical looping reaction process

Chemical looping combustion relies on high performance oxygen carriers (OCs). Iron-based OCs have excellent overall properties, but the disadvantage of low reduction reactivity limits their application prospects. Clarification of oxygen transfer pathways and bulk phase properties is essential to improve oxygen transfer rates and increase the reactivity of OCs. High-resolution transmission electron microscopy, electron energy loss spectroscopy and X-ray photoelectron spectroscopy had been used to study the lattice oxygen transport properties, the Fe and O elemental contents and Fe elemental valence changes at different positions on the radial surface of Fe2O3 OC, as well as the related elemental compositions, atomic valence and surface energy distribution on the surface of the OC during the reduction process of OC. The results show that during the reduction process, the active components at different locations of the OC are simultaneously reduced and lattice oxygen is released. Both internal and external lattice oxygen are involved in the reaction. Besides, reaction interface is believed to be fixed at a OC surface. This study reveals the migration direction of the reduction interface and the mechanism of oxygen release in the bulk phase, and would provide a theoretical basis for the structural design of Fe-based OCs.

Electrochemical bulk and film-type oxygen sensors: Strategies for detecting extremely low concentration in hydrogen environments

Potentiometric oxygen sensors with excellent sensitivity in a low oxygen concentration range are designed based on intrinsic logarithmic response characteristics, and an asymmetric electrode structure, differentiated from conventional oxygen sensors with reference oxygen gases or parts exposed to air, is implemented. Electrolytes and electrode materials that formulate oxygen sensor devices are evaluated by comprehensively considering their reactivity to trace oxygen, oxygen ion formation, and ease of movement. The sensor using an yttria-stabilized zirconia bulk ceramic electrolyte measures the oxygen concentration in an oxygen-hydrogen mixture down to 0.5%, with a response time of 7.8 s. The sensor with a Nafion proton conductor film and a polyimide gas separation membrane allows room-temperature sensing and measures the oxygen concentration to a minimum of 2%.

New Strategy for Boosting Cathodic Performance of Protonic Ceramic Fuel Cells Through Incorporating a Superior Hydronation Second Phase

For protonic ceramic fuel cells, it is key to develop material with high intrinsic activity for oxygen activation and bulk proton conductivity enabling water formation at entire electrode surface. However, a higher water content which benefitting for the increasing proton conductivity will not only dilute the oxygen in the gas, but also suppress the O2 adsorption on the electrode surface. Herein, a new electrode design concept is proposed, that may overcome this dilemma. By introducing a second phase with high‐hydrating capability into a conventional cobalt‐free perovskite to form a unique nanocomposite electrode, high proton conductivity/concentration can be reached at low water content in atmosphere. In addition, the hydronation creates additional fast proton transport channel along the two‐phase interface. As a result, high protonic conductivity is reached, leading to a new breakthrough in performance for proton ceramic fuel cells and electrolysis cells devices among available air electrodes.

Transient rising of oxygen bubbles in a fast varying gravity

We report experiments on the transient motion of an oxygen bubble rising in liquid oxygen in a fast varying magneto-gravitational acceleration. In the set-up, a strong magnetic field gradient is applied, which creates in bulk oxygen a body force opposed to its weight. When this gravity compensation is suddenly suppressed, the resulting apparent gravity increases within a fraction of a second from 0 g0 to 0.4 g0 (where g0 is the terrestrial gravitational acceleration). Oxygen bubbles of diameters ranging from 6 mm to 18 mm rise rapidly in the liquid by buoyancy, for values of Galilei and Bond numbers rarely reached with common fluids in terrestrial gravity. The shape of the bubble interface is initially ellipsoidal and evolves toward more complicated shapes during the motion. The time-dependent rising velocity of the bubble is measured during the fast variation of gravity. A comparison of the transient bubble dynamics with classical results obtained in a constant gravity environment enables the time scale of the gravity variation to be precisely quantified.

Oxidation of soot in gasoline exhaust on Mn2O3 catalyst

A Mn2O3 catalyst was investigated for soot oxidation in gasoline exhaust. Catalytic studies performed in model exhaust with Mn2O3/soot mixtures in tight contact showed efficient soot oxidation above 250 °C. This high performance was additionally confirmed on a gasoline engine test bench using a Mn2O3-coated particulate filter. The mechanism of the oxygen transport from the gas phase to soot was investigated by kinetic modeling of O2 adsorption and desorption as well as catalytic studies using 18O2. As a result, it was suggested that O2 dissociatively adsorbs on Mn2O3 followed by surface migration and transfer of oxygen to the soot at physical contact points between the two solids. The surface, sub-surface and bulk oxygen of the catalyst were also found to play a role. Enhanced participation of bulk oxygen appeared with declining O2 content due to partial reduction of Mn2O3 and formation of oxygen vacancies driving the oxygen mobility.

Tailoring Ion Ordering in Perovskite Oxide for High-Temperature Oxygen Evolution Reaction.

Perovskites exhibit excellent high-temperature oxygen evolution reaction (OER) activities as the anodes of solid oxide electrolysis cells (SOECs). However, the relationship between ion ordering and OER performances is rarely investigated. Herein, a series of PrBaCo2-x Fex O5+δ perovskites with tailored ion orderings are constructed. Physicochemical characterizations and density functional theory calculations confirm that the oxygen bulk migration and surface transport capacities as well as the OER activities are promoted by the A-site cation ordering, but weakened by the oxygen vacancy ordering. Hence, SOEC with the A-site-ordered and oxygen-vacancy-disordered PrBaCo2 O5+δ anode exhibits the highest performance of 3.40 A cm-2 at 800 °C and 2.0 V. This work sheds light on the critical role of ion orderings in the high-temperature OER performance and paves a new way for screening novel anode materials of SOECs.

Tailoring Ion Ordering in Perovskite Oxide for High‐Temperature Oxygen Evolution Reaction

AbstractPerovskites exhibit excellent high‐temperature oxygen evolution reaction (OER) activities as the anodes of solid oxide electrolysis cells (SOECs). However, the relationship between ion ordering and OER performances is rarely investigated. Herein, a series of PrBaCo2−xFexO5+δ perovskites with tailored ion orderings are constructed. Physicochemical characterizations and density functional theory calculations confirm that the oxygen bulk migration and surface transport capacities as well as the OER activities are promoted by the A‐site cation ordering, but weakened by the oxygen vacancy ordering. Hence, SOEC with the A‐site‐ordered and oxygen‐vacancy‐disordered PrBaCo2O5+δ anode exhibits the highest performance of 3.40 A cm−2 at 800 °C and 2.0 V. This work sheds light on the critical role of ion orderings in the high‐temperature OER performance and paves a new way for screening novel anode materials of SOECs.

The mechanism of nanozyme activity of ZnO–Co3O4−v: Oxygen vacancy dynamic change and bilayer electron transfer pathway for wound healing and virtual reality revealing

Since the catalyst's surface was the major active location, the inner structure's contribution to catalytic activity was typically overlooked. Here, ZnO–Co3O4−v nanozymes with several surfaces and bulk oxygen vacancies were created. The O atoms of H2O2 moved inward to preferentially fill the oxygen vacancies in the interior and form new “lattice oxygen” by the X-ray photoelectron spectroscopy depth analysis and X-ray absorption fine structure. The internal Co2+ continually transferred electrons to the surface for a continuous catalytic reaction, which generated a significant amount of reactive oxygen species. Inner and outer double-layer electron cycles accompanied this process. A three-dimensional model of ZnO–Co3O4−v was constructed using virtual reality interactive modelling technology to illustrate nanozyme catalysis. Moreover, the bactericidal rate of ZnO–Co3O4−v for Methionine-resistant Staphylococcus aureus and Multiple drug resistant Escherichia coli was as high as 99%. ZnO–Co3O4−v was biocompatible and might be utilized to heal wounds following Methionine-resistant Staphylococcus aureus infection. This work offered a new idea for nanozymes to replace of conventional antibacterial medications.

Late Middle Jurassic aridification event in the Qaidam Basin, Northwest China: palynological and geochemical evidences

Jurassic is characterized by a highly fluctuating climate. During the late Middle to Late Jurassic, Northwest China, including the Qaidam Basin, underwent a major climate transition from humid to arid conditions. In this study, we focused on the climate transitional interval (Bathonian Stage, Jurassic) and conducted high-resolution palynological and geochemical analysis to constrain more accurately this aridification event. We found that at the uppermost part of the Middle Jurassic Shimengou Formation, the relative abundance of Classopollis pollen increases along with a dramatic drop in the chemical index of alteration (CIA) and C-value, indicating a significant climate transition from humid to arid conditions during late Bathonian. Other geochemical proxy indicators, such as salinity and bulk carbonate carbon and oxygen isotopes, suggest the lacustrine environment of a closed saline lake. These significant changes indicate an environment of flourished xerophytic vegetation, weakened chemical weathering and enhanced lake salinization in the Qaidam Basin during late Bathonian, a critical turning point of the late Middle Jurassic climate from humid to arid conditions in the area, instead of Callovian (the red bed) as previously suggested.

Theoretical Investigation of the Electrochemical Oxidation of H2 and CO Fuels on a Ruddlesden-Popper SrLaFeO4-δ Anode.

The electrochemical oxidation of H2 and CO fuels have been investigated on the Ruddlesden-Popper layered perovskite SrLaFeO4-δ (SLF) under anodic solid oxide fuel cell conditions using periodic density functional theory and microkinetic modeling techniques. Two distinct FeO2-plane-terminated surface models differing in terms of the underlying rock salt layer (SrO or LaO) are used to identify the active site and limiting factors for the electro-oxidation of H2, CO, and syngas fuels. Microkinetic modeling predicted an order of magnitude higher turnover frequency for the electro-oxidation of H2 compared to CO for SLF at short-circuit conditions. The surface model with an underlying SrO layer was found to be more active with respect to H2 oxidation than the LaO-based surface model. At an operating voltage of less than 0.7 V, surface H2O/CO2 formation was found to be the key rate-limiting step, and the surface H2O/CO2 desorption was the key charge transfer step. In contrast, the bulk oxygen migration process was found to affect the overall rate at high cell voltage conditions above 0.9 V. In the presence of syngas fuel, the overall electrochemical activity is derived mainly from H2 electro-oxidation and CO2 is chemically shifted to CO via the reverse water-gas shift reaction. Substitutional doping of a surface Fe atom with Co, Ni, and Mn revealed that the H2 electro-oxidation activity of FeO2-plane terminated anodes with an underlying LaO rock salt layer can be improved with dopant introduction, with Co yielding a three orders of magnitude higher activity relative to the undoped LaO surface model. Constrained ab initio thermodynamic analysis furthermore suggested that the SLF anodes are resistant toward sulfur poisoning both in the presence and absence of dopants. Our findings reflect the role of various elements in controlling the fuel oxidation activity of SLF anodes that could aid the development of new Ruddlesden-Popper phase materials for fuel cell applications.

Designing highly active core/shell cathode materials for low-temperature PCFCs

Designing a cathode with exceptional oxygen reduction reaction (ORR) activity and durability at intermediate-to-low temperatures is vital to increase the improvement of solid oxide fuel cells (SOFCs), a captivating energy conversion technology with reduced environmental impact and high performance. Cathodes made of perovskite oxides have been developed extensively. Doping is a crucial method for modifying perovskites' lattice diffusion and surface exchange properties to achieve desired catalytic performances in a wide range of redox reactions, including oxygen reduction reactions (ORRs) for ceramic fuel cells (CFCs). The reported BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) is a potential cathode in CFCs. Here, we systematically explore the partial doping of B-sites with Al of varied content (from 5% to 30%) to further enhance the performance of BCFZY at lower temperatures. The polarization impedance of proton ion conducting fuel cells is lowest in Ba(Co0.4Fe0.4Zr0.1Y0.1)0.90Al0.1O3-δ (BCFZYA). The oxygen mobility, surface exchange kinetics, and bulk oxygen ion conductivity are all enhanced by 10%Al doping, as determined by EIS and performance tests.Moreover, Al doping led to the formation of the core-shell structure during the rearrangement of atoms. This results in an oxygen reduction reaction (ORR) of up to 0.157 cm2 at 520 oC on proton ion conducting electrolytes. As a result, BCFZYA appears to be a strong candidate for use in the cathode of advanced PCFCs (proton ceramic fuel cells).

Boosting oxygen activation in ceria-oxide via gallium addition

CeO2 is a well-suited support due to its higher oxygen storage capacity and reversible redox ability, which is associated with the oxygen activation. Herein we report the effective oxygen activation in CeO2 by gallium incorporation, varying the Ga/Ce molar ratios from 0.25 to 0.75. Structural results and operando spectroscopies under reaction conditions revealed that gallium incorporation improves the oxygen activation in CeO2, being more effective at low gallium content (Ga/Ce of 0.25). Atomic-scale computations demonstrated that the 0.25 Ga/Ce molar ratio generates Ga atomic-size channels that allow an easy way for oxygen diffusion from bulk to the surface. Ga incorporates into the subsurface Ce layer causing a collective effect: weakening the surface Ce-O bonds, boosting the surface oxygen activation, then enhancing the CO oxidation ability. Once this happens, it leaves behind O-vacancies, which may occupy either bulk oxygen from the CeO2 or further renovation of oxygen atoms from the environment.

Photothermal Cocatalytic Carbonylation of Isobutyl Amine with CO2 over Bi2O3 Polymorphs under Visible-Light Irradiation

Effective capture and utilization of CO2 is critical to reduce greenhouse gas emissions and to reach the low-carbon economy target. Herein, bismuth oxides with four different crystallized phases (α-, β-, δ-, γ-) are successfully synthesized and employed for the first time as photo, thermal, and photothermal catalysts for the successful catalytic carbonylation of isobutyl amine with CO2 to N,N′-diisobutylurea. The results displayed that the photothermal catalytic performances of Bi2O3 polymorphs followed the order of α-Bi2O3 > δ-Bi2O3 > γ-Bi2O3 > β-Bi2O3, in which the conversion of i-BuNH2 and the selectivity of N,N′-diisobutylurea for α-Bi2O3 was 50.38% and 91.79%, respectively, using N-methyl-2-pirrolidinone (NMP) as solvent and 500 W Xe lamp as the light source under the conditions of 1.0 MPa CO2 (initial pressure at room temperature) and 4 h reaction time at 100 °C. Further characterization of Bi2O3 polymorphs including XRD, SEM, BET, XPS, EPR, TPC, PL, and UV–vis absorption spectra reveals that such differences in the photothermal catalytic activity of Bi2O3 could be closely related to the efficiencies of photoinduced carriers separation. And the surface oxygen vacancies rather than bulk oxygen vacancies are favorable for the improvement of their both thermal and photothermal catalytic performances in the carbonylation of i-BuNH2 with CO2.

Catalytic methane combustion at low temperatures over YSZ-supported metal oxides: Evidence for lattice oxygen participation via the use of C18O2

Catalytic methane combustion was carried out over YSZ, Pd/YSZ and Rh/YSZ between 200 and 700 °C. Despite similar light-off curves for Pd/YSZ and Rh/YSZ between 200 and 450 °C, isotopic exchange experiments using CD4 and 18O2 revealed different behaviour of both supported catalysts regarding the activation of reactant molecules. The use of C18O2 isotopic gas was shown to be more appropriate than 18O2 to evaluate the bulk oxygen mobility in YSZ at low temperatures. The exchange of gaseous CO2 with lattice YSZ oxygen atoms, which occurs via surface hydrogen carbonate intermediate species, allowed to demonstrate the contribution of bulk oxygen atoms of YSZ in Rh/YSZ at low temperatures.

Boosting the performance of Co-doped CeO2 catalyst in the catalytic oxidation of toluene by modulating oxygen vacancies

Metal doping is one of the most effective strategies to enhance redox capacity and modulate the oxygen vacancies in Ce-based catalysts. This manuscript reports a Co-doped CeO2 catalyst (Co0.2Ce0.8 (W/E = 1/1)) for the catalytic oxidation of toluene fabricated by a facile co-precipitation method. The appropriate ratio of deionized (DI) water/ethanol in the reaction solvent contributed to the mesocrystallization of the CeO2 phase and the highly uniform dispersion of the Co-O-Ce mixed bond in the catalyst. The feasible lattice distortion induced the generation of richer oxygen vacancies in both the surface and bulk of the catalyst. Meanwhile, the efficient cycle of Co2+ + Ce4+ ↔ Co3+ + Ce3+ enhanced the redox property of the catalyst. As revealed by in situ DRIFTS studies, the as-formed surface oxygen vacancies promoted the adsorption and partial oxidation of toluene. The oxygen vacancies in the bulk of the catalyst improved the migration of lattice oxygen, accelerating the mineralization of the aromatic ring. Thus, the excellent low-temperature oxidation of toluene by Co0.2Ce0.8 (W/E = 1/1), reducing T90 to 192 °C, was attributed to the synergism between the catalyst’s surface and bulk oxygen vacancies.

Surface modification of boron cobalt complexes to enhance cycling performance of cobalt-free Li-rich cathode materials

The instability of the anionic redox reaction and the resulting irreversible oxygen release are the core causes of the deterioration of the cycling stability of Li-rich cathode materials (LRM). The effective method is to establish a surface coating on the LRM, which is equivalent to converting surface oxygen on the LRM into bulk oxygen. However, developing a coating that can form a solid binding with the surface oxygen of the LRM remains challenging. To solve the above challenge, a uniform surface boron cobalt complexes (BCCs) coating was constructed on cobalt-free LRM. The constructed BCCs coating can significantly mitigate the interface side reaction, Mn dissolution, and irreversible gas release, and enhance structural stability. The cycling stability shows that the modified LRM cathode exhibits superior capacity retention (92.7 %) compared to that of the pristine LRM cathode (78.1 %) after 300 cycles at 1 C. This modification strategy heralds a useful paradigm for optimizing the cycling stability of LRM to promote their commercial application.

The formation and aqueous alteration of CM2 chondrites and their relationship to CO3 chondrites: A fresh isotopic (O, Cd, Cr, Si, Te, Ti, and Zn) perspective from the Winchcombe CM2 fall

AbstractAs part of an integrated consortium study, we have undertaken O, Cd, Cr, Si, Te, Ti, and Zn whole rock isotopic measurements of the Winchcombe CM2 meteorite. δ66Zn values determined for two Winchcombe aliquots are +0.29 ± 0.05‰ (2SD) and +0.45 ± 0.05‰ (2SD). The difference between these analyses likely reflects sample heterogeneity. Zn isotope compositions for Winchcombe show excellent agreement with published CM2 data. δ114Cd for a single Winchcombe aliquot is +0.29 ± 0.04‰ (2SD), which is close to a previous result for Murchison. δ130Te values for three aliquots gave indistinguishable results, with a mean value of +0.62 ± 0.01‰ (2SD) and are essentially identical to published values for CM2s. ε53Cr and ε54Cr for Winchcombe are 0.319 ± 0.029 (2SE) and 0.775 ± 0.067 (2SE), respectively. Based on its Cr isotopic composition, Winchcombe plots close to other CM2 chondrites. ε50Ti and ε46Ti values for Winchcombe are 3.21 ± 0.09 (2SE) and 0.46 ± 0.08 (2SE), respectively, and are in line with recently published data for CM2s. The δ30Si composition of Winchcombe is −0.50 ± 0.06‰ (2SD, n = 11) and is essentially indistinguishable from measurements obtained on other CM2 chondrites. In conformity with petrographic observations, oxygen isotope analyses of both bulk and micromilled fractions from Winchcombe clearly demonstrate that its parent body experienced extensive aqueous alteration. The style of alteration exhibited by Winchcombe is consistent with relatively closed system processes. Analysis of different fractions within Winchcombe broadly support the view that, while different lithologies within an individual CM2 meteorite can be highly variable, each meteorite is characterized by a predominant alteration type. Mixing of different lithologies within a regolith environment to form cataclastic matrix is supported by oxygen isotope analysis of micromilled fractions from Winchcombe. Previously unpublished bulk oxygen isotope data for 12 CM2 chondrites, when combined with published data, define a well‐constrained regression line with a slope of 0.77. Winchcombe analyses define a more limited linear trend at the isotopically heavy, more aqueously altered, end of the slope 0.77 CM2 array. The CM2 slope 0.77 array intersects the oxygen isotope field of CO3 falls, indicating that the unaltered precursor material to the CMs was essentially identical in oxygen isotope composition to the CO3 falls. Our data are consistent with earlier suggestions that the main differences between the CO3s and CM2s reflect differing amounts of water ice that co‐accreted into their respective parent bodies, being high in the case of CM2s and low in the case of CO3s. The small difference in Si isotope compositions between the CM and CO meteorites can be explained by different proportions of matrix versus refractory silicates. CMs and COs may also be indistinguishable with respect to Ti and Cr isotopes; however, further analysis is required to test this possibility. The close relationship between CO3 and CM2 chondrites revealed by our data supports the emerging view that the snow line within protoplanetary disks marks an important zone of planetesimal accretion.

Surface Defect Engineering in Colored TiO2 Hollow Spheres Toward Efficient Photocatalysis (Adv. Funct. Mater. 22/2023)

Hierarchical Nanostructures In article number 2212486, Elisa Moretti, Alberto Vomiero, and co-workers, applied TiO2 hollow spheres with defect-engineered surface as highly efficient photocatalysts. The hollow structure results in strongly confined solar light, and surface defects boost the photogeneration of active charges for photocatalytic processes. Advanced spectroscopies revealed the presence of oxygen vacancies and bulk Ti3+ centers, which enabled strong photodegradation of a target drug (Ciprofloxacin) under simulated sunlight.

Enhancement of ZnO@RuO2 bifunctional photo-electro catalytic activity toward water splitting.

Catalytic materials are the greatest challenge for the commercial application of water electrolysis (WEs) and fuel cells (FCs) as clean energy technologies. There is a need to find an alternative to expensive and unavailable platinum group metal (PGM) catalysts. This study aimed to reduce the cost of PGM materials by replacing Ru with RuO2 and lowering the amount of RuO2 by adding abundant and multifunctional ZnO. A ZnO@RuO2 composite in a 10:1 molar ratio was synthesized by microwave processing of a precipitate as a green, low-cost, and fast method, and then annealed at 300°C and 600°C to improve the catalytic properties. The physicochemical properties of the ZnO@RuO2 composites were investigated by X-ray powder diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The electrochemical activity of the samples was investigated by linear sweep voltammetry in acidic and alkaline electrolytes. We observed good bifunctional catalytic activity of the ZnO@RuO2 composites toward HER and OER in both electrolytes. The improved bifunctional catalytic activity of the ZnO@RuO2 composite by annealing was discussed and attributed to the reduced number of bulk oxygen vacancies and the increased number of established heterojunctions.