Oxygen adsorption/desorption behavior of YBaCo4O7+δ and its application to oxygen removal from nitrogen

A new medium-temperature (200-400 °C) adsorbent material for oxygen removal and air separation, YBaCo4O7+δ, was prepared by the solid-state reaction method. This new adsorbent could adsorb a large quantity of oxygen in the temperature range of 200-370 °C. Adsorbed oxygen could be released by raising temperature over 400 °C or by switching the atmosphere from oxygen to nitrogen. This oxygen adsorption and desorption process had good reproducibility. Taking advantage of this unique oxygen intake/release behavior, a nitrogen purification process was investigated. The results showed that YBaCo4O7+δ material was a promising candidate for the oxygen sorption process and could be used to produce high-purity nitrogen or to remove trace oxygen from other gases.

Oxygen adsorption on pyrite (100) surface by density functional theory

Pyrite （FeS2） bulk and （100） surface properties and the oxygen adsorption on the surface were studied by using density functional theory methods. The results show that in the formation of FeS2 （100） surface, there exists a process of electron transfer from Fe dangling bond to S dangling bond. In this situation, surface Fe and S atoms have more ionic properties. Both Fe2+ and S2- have high electrochemistry reduction activity, which is the base for oxygen adsorption. From the viewpoint of adsorption energy, the parallel form oxygen adsorption is in preference. The result also shows that the state of oxygen absorbed on FeS2 surface acts as peroxides rather than O2.

Clarification of the oxygen adsorption properties of YBaCo_4O_7 at high temperature by thermogravimetry

The oxygen adsorption/desorption properties of YBaCo4O7 at high temperature were investigated by thermogravimetry(TG) method,in which two types of oxygen adsorption were combined.The first type adsorbed oxygen at about 700 °C and released the adsorbed oxygen at 880 °C.After the first type oxygen desorption,even the temperature and oxygen flow were kept the same,a second type oxygen adsorption at about 880 °C occurred and the adsorbed oxygen were released at above 980 °C.The combination of these two types of...

STUDIES OF OXYGEN ADSORPTION AND INITIAL OXIDATION ON SINGLE CRYSTAL Mn_5Si_3(111) SURFACE

Kinetics of oxygen adsorption on single crystal Mn5Si3 （111） surface and initial surface oxidation were investigated. Oxygen chemisorbs dissociatively at room temperature on Mn and Si atoms. A fast oxidation of Si atoms occurs followed by oxidation of Mn atoms at RT. The MnO2 was reduced by Si atoms and the SiO was oxidized further to SiO2 during the sample heating.

Analysis of irrationality of coal susceptibility to spontaneous combustion determination method with fluid oxygen adsorption

Based on experiment results and theoretical analysis,pointed out that the method of coal susceptibility to spontaneous combustion determination with fluid oxygen adsorption can not present the essence of coal oxidation process and oxidation reaction. The method is incorrect,paying attention at one aspect and ignoring the rest.The method is not reasonable for coal susceptibility to spontaneous combustion determination.Sus- ceptibility to spontaneous combustion of coal reflects chemical property of coal oxidation with oxygen absorption and heat release at low temperature.Coal's susceptibility to spon- taneous combustion is mainly decided by the number of molecules with reaction activation energy and activation molecule production rate at certain temperature.Therefore,index of susceptibility to spontaneous combustion should adopt accumulative value or trend of heat release or oxygen adsorption during oxidation process.

Power loss transition of stable ZnO varistor ceramics: Role of oxygen adsorption on the stability of interface states at the grain boundary

Highly stable ZnO varistor ceramics with steadily decreasing power loss have been put into applications in electrical and electronic systems for overvoltage protections, even with the absence of general understandings on their aging behaviors. In this paper, we investigated their aging nature via conducting comparative direct current (DC) aging experiments both in air and in nitrogen, during which variations of electrical properties and interface properties were measured and analyzed. Notably, continuously increasing power loss with severe electrical degradation was observed for the sample aged in nitrogen. The power loss transition was discovered to be closely related to the consumption of oxygen adsorption at the grain boundary (GB), which could, however, remain constant for the sample aged in air. The interface density of states (DOS) Ni, which is crucial for pinning the potential barrier, was proved to decrease in nitrogen, but keep stable in air. Therefore, it is concluded that the oxygen adsorption at the GB is significant for the stability of interface states, which further correlates to the long-term stability of modern stable ZnO varistor ceramics.

Manipulating oxygenate adsorption on N-doped carbon by coupling with CoSn alloy for bifunctional oxygen electrocatalyst

Highly active bifunctional oxygen electrocatalysts accelerate the development of high-performance Zn-air battery,but suffer from the mismatched activities of oxygen evolution reaction(OER)and oxygen reduced reaction(ORR).Herein,highly integrated bifunctional oxygen electrocatalysts,cobalt-tin alloys coated by nitrogen doped carbon(CoSn@NC)are prepared by MOFs-derived method.In this hybrid catalyst,the binary CoSn nanoalloys mainly contribute to highly active OER process while the Co(or Sn)-N-C serves as ORR active sites.Rational interaction between CoSn and NC donates more rapid reaction kinetics than Pt/C(ORR)and IrO_(2)(OER).Such CoSn@NC holds a promise as air-cathode electrocatalyst in Zn-air battery,superior to Pt/C+IrO_(2)catalyst.First-principles calculations predict that CoSn alloys can upgrade charge redistribution on NC and promote the transfer to reactants,thus optimizing the adsorption strength of oxygen-containing intermediates to boost the overall reactivity.The tuning of oxygenate adsorption by interactions between alloy and heteroatom-doped carbon can guide the design of bifunctional oxygen electrocatalysts.

High-resolution angle-resolved photoemission study of oxygen adsorbed Fe/MgO(001)

We have investigated the electronic states of clean Fe(001) and oxygen adsorbed Fe(001)–p(1 × 1)-O films epitaxially grown on MgO(001) substrates by means of polarization-dependent angle-resolved photoemission spectroscopy(ARPES)and extensive density-functional theory(DFT) calculations. The observed Fermi surfaces and band dispersions of pure Fe near the Fermi level were modified upon oxygen adsorption. By the detailed comparison of ARPES and DFT results of the oxygen adsorbed Fe surface, we have clarified the orbital-dependent p–d hybridization in the topmost and second Fe layers.Furthermore, the observed energy levels and Fermi wave numbers for the oxygen adsorbed Fe surface were deviated from the DFT calculations depending on the orbital characters and momentum directions, indicating an anisotropic interplay of the electron correlation and p–d hybridization effects in the surface region.

Determination of the Real Surface Area of Palladium Electrode

Four methods, including voltammetric measurement of double layer capacitance, surface oxides reduction, under potential deposition of Cu and carbon monoxide （CO） stripping have been applied to evaluate the real surface area of a polycrystalline Pd （pc-Pd） electrode. The results reveal that the second and third methods lead to consistent results with deviations below 5%. And from the determined double layer capacitance and CO stripping charge, it is deduced that the double layer capacity unit area is 23.1±0.4μF/cm2 and the saturated CO adlayer should be ca. 0.66 ML in order to ensure that the real surface area as determined is consistent with the other two techniques. The applicability as well as the attentions when applying these techniques for the determination of the real surface area of pc-Pd electrodes have been discussed.

In situ decoration of CoP/Ti_(3)C_(2)Tx composite as efficient electrocatalyst for Li-oxygen battery

Application of Li-oxygen(Li-O_(2)) battery is in urgent need of bifunctional ORR/OER electrocatalyst. A surface-functionalization CoP/Ti_(3)C_(2)Txcomposite was fabricated theoretically, with the optimized electronic structure and more active electron, which is beneficial to the electrochemical reaction. The accordion shaped Ti_(3)C_(2)Txis featured with large specific surface area and outstanding electronic conductivity, which is beneficial for the adequate exposure of active sites and the deposition of Li2O2. Transition metal phosphides provide more electrocatalytic active sites and present good electrocatalytic effect. The CoP/Ti_(3)C_(2)Txcomposite served as the electrocatalyst of Li-O_(2)battery reaches a high specific discharge capacity of 17,413 m Ah/g at 100 m A/g and the lower overpotential of 1.25 V, superior to those of the CoP and Ti_(3)C_(2)Txindividually. The composite of transition metal phosphides and MXene are applied in Li-O_(2)battery, not only demonstrating higher cycling stability of the prepared CoP/Ti_(3)C_(2)Txcomposite, but pointing out the direction for their electrochemical performance improvement.

MOLECULAR DESIGN OF FUNCTIONAL POLYMERS BASED ON UNIQUE PROPERTIES OF POLYMER CHAINS

The inclusion complex formation of α-CD, β-CD, and γ-CD with various water-soluble polymers has beeninvestigated, and the relationship between the chain cross-sectional areas of the polymers and the diameters of the cavities ofcyclodextrins (molecular recognition) was found. Polyrotaxanes and tubular polymers were prepared on the basis ofmolecular recognition. Several kinds of polymers having tetraphenylporphyrin (TPP) and paramagnetic metallotetraphenyl-porphyrin (AgTPP, CuTPP, VOTPP or ZnTPP) have been prepared by radical polymerization of the correspondingmonomers. Visible spectra of these polymers show hypochromism in the Sorer bands of TPP moieties as compared withthose of monomers. Polymer effects were observed in the magnetic behavior and oxygen adsorption of paramagneticmetallotetraphenylporphyrin moieties. Moreover, polymer effects on photophysical and photochemical behavior were foundin the amphiphilic polymers covalently tethered with small amounts of zinc(Ⅱ)-tetraphenylporphyrin (ZnTPP).

Coordinatively unsaturated cobalt single-atom nanozymes for visual pesticides detection by smartphone-based platform

By adjusting the coordination environment of single-atom catalysts,the enzyme-like activity can be finely tuned for highly sensitive biosensing.Herein,we demonstrated that coordinatively unsaturated cobalt-nitrogen sites doped within porous carbon(SA-CoN_(3))could serve as highly efficient oxidase mimic.Compared with the typical planar four-coordination structure(SA-CoN_(4)),the as-obtained single-atom Co nanozymes anchored by three nitrogen atoms are found to display much higher oxidase-like catalytic efficiency.Combined theoretical and experimental analysis revealed that the coordinatively unsaturated Co sites could facilitate adsorption and activation of O_(2) molecule and thus improve their oxidase-like activity.Based on the enhanced oxidase-like activity of SA-CoN_(3),a paper/smartphone sensor for organophosphorus pesticides(OPs)was successfully constructed and used to quantify glyphosate in environmental and food samples with a low detection limit of 0.66μM.This work not only highlights the important role of coordination unsaturation of SA nanozymes for promoting oxidase-like activity,but also provides an easy and cost-effective way to conduct effective quantification of OPs in the field.

Grain boundary-induced drastic sensing performance enhancement of Fe_(2)O_(3) gas sensors for acetone

Exploring the structure-activity relationship between the performance of gas sensors and the structure of semiconductor metal oxide(SMO)nanomaterials is crucial for understanding and designing gas-sensing materials and overcoming the application limitations of SMO-based gas sensors.Regulation of a single SMO microstructure provides a promising solution to address this scientific problem due to its controllable composition.In this study,we control the grain boundary(GB)density of Fe_(2)O_(3)nanomaterials using a simple solvothermal method.They have similar chemical compositions and crystal phases,providing an ideal platform for studying the influence of the GB density on the gas-sensing performance.Gas-sensing tests showed that the Fe_(2)O_(3)-1 sensor with medium GB density and the Fe_(2)O_(3)-2 sensor with high GB density had higher sensitivity and selectivity than the Fe_(2)O_(3)-0 sensors with low GB density before reaching the optimal operating temperature.However,when the GB density increased,the response to acetone decreased slightly,whereas the optimal operating temperature decreased.This work highlights the unique performance of the GB density in enhancing the gas sensitivity of a single SMO.

UV illumination enhanced desorption of oxygen molecules from monolayer MoS2 surface

The oxygen adsorption can drastically alter the electronic properties of the two-dimensional(2D)materials,which is usually dificult to be removed.In this work,we report the ultraviolet(UV)ilumination induced desorption of the O2 molecules from the monolayer MoS2 surface by using the atmosphere dependent transport measurement,Kelvin probe microscopy,photoluminescence spectroscopy and X-ray photoelectron spectroscopy.Obvious increasing of the conductivity,rising of the Fermi level,and red shift of the photoluminescence peaks of the MoS2 were observed after the UV ilumination in vacuum,indicating the elimination of the depletion effect from the oxygen adsorption.Such parameter changes can be reversibly recovered by the subsequent O2 exposure.Furthermore,obvious decreasing of the oxygen concentration after the UV ilumination was also observed by X-ray photoelectron spectroscopy.Thus the UV induced O2 photodesorption effect is evidenced.The photo-excited charge transfer mechanism is proposed to account for the photodesorption effect.These results provide a nondestructive way to clean the MoS2 surface and manipulate the performance of the MoS2 based devices.

Light-switchable catalytic activity of Cu for oxygen reduction reaction

The surface reactivity of metals is fundamentally dependent on the local electronic structure generally tailored by atomic compositions and configurations during the synthesis.Herein,we demonstrate that Cu,which is inert for oxygen reduction reaction(ORR)due to the fully occupied d-orbital,could be activated by applying a visible-light irradiation at ambient temperature.The ORR current is increased to 3.3 times higher in the potential range between-0.1 and 0.4 V under the light of 400 mW·cm^-2,and the activity enhancement is proportional to the light intensity.Together with the help of the first-principle calculation,the remarkably enhanced electrocatalytic activity is expected to stem mainly from the decreased metal-adsorbate binding by photoexcita-tion.This finding provides an additional degree of freedom for controlling and manipulating the surface reactivity of metal catalysts besides materials strategy.