Lattice Oxygen Diffusion Research Articles

Oxygen vacancy modulation for enhanced hydrogen production via chemical looping water-gas shift

Oxygen vacancy modulation for enhanced hydrogen production via chemical looping water-gas shift

Enhanced reactivity over Ce2(SO4)3/MgO with NiO modification for chemical looping partial oxidation of methane

Enhanced reactivity over Ce2(SO4)3/MgO with NiO modification for chemical looping partial oxidation of methane

Kinetic analysis of biochar chemical looping gasification with calcium ferrite as oxygen carriers

Kinetic analysis of biochar chemical looping gasification with calcium ferrite as oxygen carriers

Suppressing the lattice oxygen diffusion via high-entropy oxide construction towards stabilized acidic water oxidation

Suppressing the lattice oxygen diffusion via high-entropy oxide construction towards stabilized acidic water oxidation

The effect of duct size, sample size, and fuel composition on concurrent flame spread over large cellulose samples in microgravity

Concurrent flame spread data for thermally-thin charring solid fuels are presented from Saffire and BASS experiments performed in habitable spacecraft for three duct sizes, five sample sizes, two materials, and two atmospheres. The flame spread rates and flame lengths were strongly affected by duct size even for the relatively large ducts (> 30 cm tall). A transient excess pyrolysis length (i.e., flame length overshoot) was observed for the cotton fabric that burned away, which indicates that the transient excess pyrolysis length phenomenon is caused by more than just the flame moving into the developing boundary layer thickness as was the case with the SIBAL sample. A burnout time, defined as the pyrolysis length divided by the flame spread rate, normalized the pyrolysis length histories into a single curve with a steady burnout time of 22 s for the SIBAL fabric. The transient excess pyrolysis length is hypothesized to be a post-ignition flame growth transient for the essentially two-dimensional flames where the burnout time becomes very long until the preheat and pyrolysis lengths develop. The three-dimensional flames over narrow samples have lateral thermal expansion and lateral oxygen diffusion which allows them to transition to a steady state length without the transient excess pyrolysis length. Surface temperature profiles, nondimensionalized by the pyrolysis length, indicate that the temperature profiles exhibit the same shape across the pyrolysis zone. A surface energy balance calculation in the preheat region revealed that the heat flux increased rapidly at the pyrolysis front to near the critical heat flux for ignition. An estimate of the acceleration of the inviscid core flow in the duct due to thermal expansion and developing boundary layers on the duct walls and the SIBAL sample surface seems to explain the observed spread rate trends across three duct sizes and multiple sample sizes.

Enhanced oxygen bulk diffusion of La0.6Sr0.4FeO3-δ fuel electrode by high valence transition metal doping for direct CO2 electrolysis in solid oxide electrolysis cells

Enhanced oxygen bulk diffusion of La0.6Sr0.4FeO3-δ fuel electrode by high valence transition metal doping for direct CO2 electrolysis in solid oxide electrolysis cells

Simultaneously Improved Surface and Bulk Participation of Evolved Perovskite Oxide for Boosting Oxygen Evolution Reaction Activity Using a Dynamic Cation Exchange Strategy.

Perovskite oxides are intriguing electrocatalysts for the oxygen evolution reaction, but both surface (e.g., composition) and bulk (e.g., lattice oxygen) properties should be optimized to maximize their participation in offering favorable activity and durability. In this work, it is demonstrated that through introducing exogenous Fe3+ ( ) into the liquid electrolyte, not only is the reconstructed surface stabilized and optimized, but the lattice oxygen diffusion is also accelerated. As a result, compared to that in Fe-free 0.1m KOH, PrBa0.5 Sr0.5 Co2 O5+δ in 0.1m KOH + 0.1mm Fe3+ demonstrates a tenfold increment in activity, an extremely low Tafel slope of ≈50mVdec-1 , and outstanding stability at 10.0mAcm-2 for 10h. The superior activity and stability are further demonstrated in Zn-air batteries by presenting high open-circuit voltage, narrow potential gap, high power output, and long-term cycle stability (500cycles). Based on experimental and theoretical calculations, it is discovered that the dynamical interaction between the Co hydr(oxy)oxide from surface reconstruction and intentional Fe3+ from the electrolyte plays an important role in the enhanced activity and durability, while the generation of a perovskite-hydr(oxy)oxide heterostructure improves the lattice oxygen diffusion to facilitate lattice oxygen participation and enhances the stability.

Migration Mechanism of Lattice Oxygen: Conversion of CO2 to CO Using NiFe2O4 Spinel Oxygen Carrier in Chemical Looping Reactions

CO2 resourceful utilization contributes to the goal of carbon neutrality. Chemical Looping Dry Reforming (CLDR) has attracted significant attention as a method for converting CO2 to CO. NiFe2O4 oxygen carrier (OC) is found to be a potential material for CLDR. However, the migration process of lattice oxygen, which are critical for the conversion of CO2 to CO, was not extensively investigated. In this study, the reduction and oxidation degrees of the NiFe2O4 were finely modulated in a thermogravimetric analyzer. The lattice oxygen migration mechanism of the NiFe2O4 in redox cycles was characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and in-situ Raman. The novelty of this paper is clarifying the release-uptake paths of lattice oxygen during CO2 resourceful utilization. The result indicates that the concentration gradient between the surface and the bulk drives the diffusion of lattice oxygen. The stabilization of surface lattice oxygen content is attributed to the rapid migration of O anion, which is closely associated with the movement process of Ni particles inward and outward through the spinel bulk. In addition, a highly reactive chemical reaction interface consisting of lattice oxygen and the corresponding metal atoms is always present on the surface of the oxygen carrier and is confirmed by an in-situ Raman and XPS during the whole process of CLDR. The results of this paper offer reference and basis for further development and design of CLDR using spinel OC.

Ultrafine Pd species anchored on porous CeO2 nanobundles as a highly efficient catalyst for methane oxidation

Ultrafine Pd species embedded in porous CeO 2 matrix derived from Ce-MOFs were facilely prepared. The mixed chemical states of Pd species along with abundant oxygen vacancies contribute to high catalytic activity. • Pd/CeO 2 nanobundles derived Ce-MOF were facilely prepared. • Unltrafine Pd species are homogeneously embedded in porous CeO 2 matrix. • The Pd/CeO 2 nanobundles show obviously improved catalytic activity at low temperature. • Mixed chemical states of Pd species along with abundant oxygen vacancy contribute to high activity. The design and development of efficient catalyst is very important for the removal of air pollutants through catalytic oxidation technology. Here, the Pd/CeO 2 catalysts were synthesized via in-situ thermal pyrolysis of Pd 2+ doped Ce-MOF. The prepared Pd/CeO 2 -NB catalyst exhibits nanobundles structure and highly dispersed Pd species, which shows superior performance in CO oxidation and CH 4 combustion at low temperature (<400 °C). The Raman, XPS, TPR and CO-IR reveal that the Pd/CeO 2 -NB sample has a certain surface concentration of Pd 0 species, and the formed Pd/PdO species boost the generation of oxygen vacancies, facilitating the dissociation of gas oxygen and the diffusion of lattice oxygen. Besides, possible reaction mechanism is also clarified by in-situ DRIFTS spectra, and main surface intermediate species (carbonate and carbon oxygenates) were confirmed. This study paves a way for the design of MOFs-based catalytic materials.

Ce-modified SrFeO3-δ for ethane oxidative dehydrogenation coupled with CO2 splitting via a chemical looping scheme

The current study investigates Ce-modified SrFeO 3- δ oxygen carriers for oxidative dehydrogenation (ODH) of ethane coupled with CO 2 splitting in a chemical looping manner. During 39 cycles of redox testing over the sample of 0.2Ce/SrFeO 3 , up to 29% ethane conversion and 82% ethylene selectivity are achieved, and the CO generation in the subsequent CO 2 splitting step is 0.25 mmol/g. XPS characterization results indicate decreased Fe 2+ /(Fe 3+ +Fe 4+ ) ratio as well as increased active oxygen species proportion on the near-surface of Ce-modified samples, which are responsible for the improved activity of the 0.2Ce/SrFeO 3 in ethane ODH reaction. DFT calculations further reveal that the increased ODH activity of 0.2Ce/SrFeO 3 is due to the lower surface oxygen vacancy formation energy upon Ce promotion. Moreover, the higher resistance of lattice oxygen diffusion from the bulk to the surface is the main reason for the superior ethylene selectivity attained by the CO 2 -regenerated sample than that by O 2 regeneration. 0.2Ce/SrFeO 3 stimulates ethane and CO 2 valorization successively via ethane oxidative dehydrogenation coupled with CO 2 splitting in a chemical looping manner. • 0.2Ce/SrFeO 3 enables ethane and CO 2 valorization successively via chemical looping. • Ce addition facilitates perovskite phase formation at milder calcination condition. • CO 2 regeneration of the sample leads to better ODH performance than that by O 2 . • DFT reveals a lower surface oxygen formation energy on the Ce modified sample.

First-principles-based microkinetic rate equation theory for oxygen carrier reduction in chemical looping

The reduction kinetics of oxygen carriers with reacting gases are typically modeled using shrinking-core-based models, in which, the elemental surface reaction mechanisms are simplified as only one global reaction, and the kinetic parameters are obtained by fitting with experimental data. In this study, a theoretical scheme is proposed to couple the elemental surface reaction mechanisms with the bulk diffusion of lattice oxygen, and a first-principle-based microkinetic rate equation theory is developed to model the reduction kinetics of oxygen carrier in chemical looping. The elemental surface reaction mechanisms are computed using quantum chemistry and are integrated into the mean-field microkinetic model, in which, oxygen bulk diffusion is also included. The elemental steps of gas adsorption, surface reaction, and surface species desorption are considered in the theory. The kinetic parameters used in the model are directly calculated by using transition state theory and density functional theory instead of fitting with experimental data. The developed theory is applied to predict the reduction kinetics of a CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite oxygen carrier and validated to accurately predict the reduction kinetics by H2 and CO under a wide range of temperatures and gas concentrations. The effect of surface reaction and bulk diffusion on the overall reaction rate is analyzed and the rate-controlling step is discussed. When the bulk diffusion is considerably rapid, the interior oxygen concentration in the grain remains uniform throughout the reduction process and can be considered as a function of time only. Lumped parameter analysis is used to simplify the bulk diffusion of lattice oxygen without sacrificing accuracy. The developed microkinetic rate equation theory couples the surface reaction mechanism with the bulk diffusion, bridges the gap between atom-scale first-principles quantum chemistry calculations with particle-scale heterogeneous kinetics, and provides a theoretical framework for oxygen carrier reduction/oxidation kinetics, gas conversion mechanisms, and product selectivity in chemical looping.

Effect of calcination temperature on the performance of hexaaluminate supported CeO2 for chemical looping dry reforming

The chemical looping dry reforming (CLDR) of methane is a novel syngas production and CO2 utilization technology via the circulation of oxygen carrier. In this work, BaFe3Al9O19 (BF3) hexaaluminate supported CeO2 serves as oxygen carrier for CLDR. Combined with a series of characterization, the effect of interaction between CeO2 and hexaaluminate as a function of calcination temperatures (700, 800, 900 and 1000 °C) on the CLDR performance was carefully investigated, and then the possible reaction mechanism was proposed. The results show that fresh CeO2/BF3 is composed of CeO2, β-Al2O3 and magnetoplumite (MP) hexaaluminate. Increasing the calcination temperature from 700 to 900 °C is conducive to enhancing the interaction strength between CeO2 and hexaaluminate, which favors the diffusion of lattice oxygen to the surface. However, 1000 °C calcination leads to the sintering of oxygen carrier, which hinders the migration of lattice oxygen. Among CeO2/BF3-T (T = 700–1000 °C), CeO2/BF3–900 °C presents not only a high methane conversion (~85%), high syngas yield (1.28–2.02 mmol/g) with ideal H2/CO ratio (~2), but also excellent CO2 activation ability and cyclic stability in the periodic CH4/CO2 redox cycles. The results were mainly attributed to the highest concentration of Ce3+ and Fe2+, abundant oxygen vacancies and the formation of CeFexAl1-xO3.

Thermal Conductivity and Oxygen Tracer Diffusion of Yttria Stabilized Zirconia by Molecular Dynamics

One of the most technologically beneficial engineering ceramics is yttria stabilized zirconia (YSZ). As a result, research interest about YSZ has been intensive for many years. In this study, the lattice thermal conductivity and oxygen diffusion coefficient of YSZ are investigated at different temperatures (from 700 K to 1300 K) and zero pressure with the Green-Kubo formalism. We find that the lattice thermal conductivity decreases as the temperature increases, particularly at low temperatures and it shows a slightly temperature independence at high temperatures. The results demonstrate that the YSZ has quite a low thermal conductivity compared with pure zirconia. We also show that the oxygen tracer diffusion coefficient, as calculated from the mean square displacements, has an activation energy of 0.85eV.

How does oxygen diffuse from capillaries to tissue mitochondria? Barriers and pathways.

Timely delivery of oxygen (O2 ) to tissue mitochondria is so essential that elaborate circulatory systems have evolved to minimize diffusion distances within tissue. Yet, knowledge is surprisingly limited regarding the diffusion pathway between blood capillaries and tissue mitochondria. An established and growing body of work examines the influence cellular and extracellular structures may have on subcellular oxygen availability. This brief review discusses the physiological and pathophysiological significance of oxygen availability, highlights recent computer modelling studies of transport at the cell-membrane level, and considers alternative diffusion pathways within tissue. Experimental and computer modelling studies suggest that oxygen diffusion may be accelerated by cellular lipids, relative to cytosolic and interstitial fluids. Such acceleration, or 'channelling', would occur due to greatly enhanced oxygen solubility in lipids, especially near the midplane of lipid bilayers. Rapid long-range movement would be promoted by anisotropically enhanced lateral diffusion of oxygen along the midplane and by junctions holding lipid structures in close proximity to one another throughout the tissue. Clarifying the biophysical mechanism of oxygen transport within tissue will shed light on limitations and opportunities in tumour radiotherapy and tissue engineering.

Modified CeO2 as active support for iron oxides to enhance chemical looping hydrogen generation performance

Abstract Chemical looping hydrogen generation (CLG) is a promising pathway that can offer both the high purity hydrogen as well as the efficient CO2 capture capability. However, this process was significantly hindered by the lack of active oxygen carriers at relatively low temperatures. Mixed ionic-electronic (MIEC) supported iron oxides exhibit desirable redox performance for the improved oxygen-ion conductivity. In this work, we prepared several AxCe1-xO2-δ (A = Gd, La; x = 0, 0.1, 0.3) supported Fe2O3 for hydrogen production at 750 °C. It was shown that Fe2O3/Gd0.3Ce0.7O2-δ shows the highest hydrogen generation performance and stability over 50 redox cycles. The reactivity follows the sequence of: Fe2O3/Gd0.3Ce0.7O2-δ > Fe2O3/La0.1Ce0.9O2-δ > Fe2O3/Gd0.1Ce0.9O2-δ > Fe2O3/La0.3Ce0.7O2-δ. The fundamental investigation shows that the doping of rare earth (Gd, La) into CeO2 contributes to the formation of oxygen vacancies, thus improving the lattice oxygen diffusion. The enhanced hydrogen generation performance attributes to the high lattice oxygen diffusion to improve the reactivity and inhibiting outward diffusion of Fe. The roughly linear relation between the oxygen vacancy concentration and chemical looping performance can be extended to predict the performance of oxygen carriers for other chemical looping applications, methane reforming, combustion, and ethane dehydrogenation, etc.

Isotopic Oxygen Exchange Study to Unravel Noble Metal Oxide/Support Interactions: The Case of RuO2 and IrO2 Nanoparticles Supported on CeO2, TiO2 and YSZ

AbstractThe aim of this study is to unravel the mechanism of (noble metal oxide)/(active support) interactions for catalytic purposes. Hence, isotopic oxygen exchange (IOE) tests were performed on Iridium‐ and ruthenium‐based oxides supported on cerium oxide (CeO2), titanium oxide (TiO2), and yttria‐stabilized zirconia (YSZ). IOE tests demonstrated the metal oxide support involvement in the propane oxidation reaction, with YSZ‐based catalysts showing the highest exchange rate of oxygen, while CeO2 and TiO2‐based catalysts had a less diffusion of lattice oxygen in that order. This is related to the presence of extrinsic oxygen vacancies in the YSZ‐based catalysts and the reduction ability of the CeO2 and TiO2 supports. Despite the limitations on oxygen exchange in some of the noble/metal oxide catalysts, their catalytic performance was comparable to the ones that showed a high oxygen exchange. Therefore, active supports results in a higher engagement of oxygen from the support but not in a linear correlation with the catalytic performance of the metal/support.

Strong Cathodoluminescence and Fast Photoresponse from Embedded CH3NH3PbBr3 Nanoparticles Exhibiting High Ambient Stability.

This study presents a comprehensive analysis of the strong cathodoluminescence (CL), photoluminescence (PL), and photoresponse characteristics of CH3NH3PbBr3 nanoparticles (NPs) embedded in a mesoporous nanowire (NW) template. Our study revealed a direct correlation between the CL and PL emissions from the perovskite NPs (Per NPs), for the first time. Per NPs are fabricated by a simple spin-coating of a perovskite precursor on the surface of metal-assisted chemically etched mesoporous Si NW arrays. The Per NPs confined in the mesopores show blue-shifted and enhanced CL emission as compared to the bare perovskite film, while the PL intensity of Per NPs is dramatically high compared to that of their bulk counterpart. A systematic analysis of the CL/PL spectra reveals that the quantum confinement effect and ultralow defects in Per NPs are mainly responsible for the enhanced CL and PL emissions. Low-temperature PL and time-resolved PL analysis confirm the high exciton binding energy and radiative recombination in Per NPs. The room temperature PL quantum yield of the Per NP film on the NW template was found to be 40.5%, while that of Per film was 2.8%. The Per NPs show improved ambient air stability than the bare film due to the protection provided by the dense NW array, since a dense NW array can slow down the lateral diffusion of oxygen and water molecules in Per NPs. Interestingly, the Si NW/Per NP junction shows superior visible light photodetection and the prototype photodetector shows a high responsivity (0.223 A/W) with response speeds of 0.32 and 0.28 s of growth and decay in photocurrent, respectively, at 2 V applied bias, which is significantly better than the reported photodetectors based on CH3NH3PbBr3 nanostructures. This work demonstrates a low-cost fabrication of CH3NH3PbBr3 NPs on a novel porous NW template, which shows excellent photophysical and optoelectronic properties with superior ambient stability.

Operando and Postreaction Diffraction Imaging of the La–Sr/CaO Catalyst in the Oxidative Coupling of Methane Reaction

A La–Sr/CaO catalyst was studied operando during the oxidative coupling of methane (OCM) reaction using the X-ray diffraction computed tomography technique. Full-pattern Rietveld analysis was performed in order to track the evolving solid-state chemistry during the temperature ramp, OCM reaction, as well as after cooling to room temperature. We observed a uniform distribution of the catalyst main components: La2O3, CaO–SrO mixed oxide, and the high-temperature rhombohedral polymorph of SrCO3. These were stable initially in the reaction; however, doubling the gas hourly space velocity resulted in the decomposition of SrCO3 to SrO, which subsequently led to the formation of a second CaO–SrO mixed oxide. These two mixed CaO–SrO oxides differed in terms of the extent of Sr incorporation into their unit cell. By applying Vegard’s law during the Rietveld refinement, it was possible to create maps showing the spatial variation of Sr occupancy in the mixed CaO–SrO oxides. The formation of the Sr-doped CaO species is expected to have an important role in this system through the enhancement of the lattice oxygen diffusion as well as increased catalyst basicity.

Investigation of electrospun Ba0.5Sr0.5Co0.8Fe0.2O3−δ-Gd0.1Ce0.9O1.95 cathodes for enhanced interfacial adhesion

Abstract Fibrous Ba0.5Sr0.5Co0.8Fe0.2O3−δ-Gd0.1Ce0.9O1.95 (BSCF-GDC) composite cathodes are fabricated by a facile electrospinning method. However, the electropun BSCF-GDC cathode shows poor adhesion to a GDC electrolyte because of the high shrinkage rate of the electrospun BSCF-GDC cathode during sintering. To solve this adhesion issue, mixed BSCF fiber-GDC powder cathode is investigated. As a result, mixed BSCF fiber-GDC powder cathode with an enhanced adhesion is successfully fabricated. This improvement can be attributed to the modified microstructure with the GDC powder that joins the BSCF fibers to the GDC electrolyte at the cathode and electrolyte interface. The polarization resistance of the mixed BSCF fiber-GDC powder cathode is 0.10 Ω cm2, which is lower than 0.13 Ω cm2 of conventional BSCF-GDC powder cathode at 700 °C. It is attributable to the improved oxygen gas and lattice oxygen diffusion, and the surface exchange of the mixed BSCF fiber-GDC powder cathode. The single cell with a mixed BSCF fiber-GDC powder cathode show 500 mW cm−2 at 700 °C, which is 25% higher than conventional BSCF-GDC powder cathode.

Effects of Co-substitution on the reactivity of double perovskite oxides LaSrFe2-xCoxO6 for the chemical-looping steam methane reforming

Abstract The double perovskite oxides (DPOs) LaSrFe2-xCoxO6 (x = 0, 0.2, 0.4, 0.6, 0.8) were investigated as oxygen carriers for the chemical looping steam methane reforming (CL-SMR). The fresh oxides were prepared by micro-emulsion method and their physical and chemical properties were characterized by X-ray diffraction, H2-temperature programmed reduction and X-ray photoelectron spectroscopy technologies. Meanwhile, isothermal reactions for methane reforming and steam splitting were carried out in a fixed-bed reactor to determine the influences of Co-substitution on the reactivity of LaSrFe2-xCoxO6. The substitution of metal Co has no obvious effect on the crystal structure of double perovskite, but induces a certain degree of Fe/Co disorder generating oxygen vacancies and/or higher oxidation states of metal cations. Synergistic interaction between surface metal ions, such as (Fe4+/Fe5+-O2--Co2+) and (Fe3+-O2--Co3+), plays a positive effect for the dissociation of methane. The activity may be more likely to be associated with the active oxygen species in connection with Co species on the DPOs surface and abundant of syngas was generated due to the concordant of methane dissociation with the lattice oxygen diffusion. Comprehensively considered, an optimal range of the degree of Co substitution is x = 0.4–0.6 for LaSrFe2-xCoxO6, probably converting 70% of CH4 into CO and H2 with molar ratio around 2:1. At the reduced states, the ability of DPOs for steam splitting is primarily associated with the oxygen vacancies after oxygen consumption. The substitution of metal Co slightly enhances the hydrogen production capacity and resistance to carbon formation, achieving the average hydrogen yields at 2.89–3.33 mmol/g oxygen carrier and 1.46–1.61 wt% of carbon depositions.