Hard-carbon hybrid Li-ion/metal anode enabled by preferred mesoporous uniform lithium growth mechanism

To achieve high energy density in lithium batteries,the construction of lithium-ion/metal hybrid anodes is a promising strategy.In particular,because of the anisotropy of graphite,hybrid anode formed by graphite/Li metal has low transport kinetics and is easy to causes the growth of lithium dendrites and accumulation of dead Li,which seriously affects the cycle life of batteries and even causes safety problems.Here,by comparing graphite with two types of hard carbon,it was found that hybrid anode formed by hard carbon and lithium metal,possessing more disordered mesoporous structure and lithophilic groups,presents better performance.Results indicate that the mesoporous structure provides abundant active site and storage space for dead lithium.With the synergistic effect of this structure and lithophilic functional groups(–COOH),the reversibility of hard carbon/lithium metal hybrid anode is maintained,promoting uniform deposition of lithium metal and alleviating formation of lithium dendrites.The hybrid anode maintains a 99.5%Coulombic efficiency(CE)after 260 cycles at a specific capacity of 500 m Ah/g.This work provides new insights into the hybrid anodes formed by carbon-based materials and lithium metal with high specific energy and fast charging ability.

Effect of Calcination Temperature on Surface Oxygen Vacancies and Catalytic Performance Towards CO Oxidation of Co3O4 Nanoparticles Supported on SiO2

Co3O4/SiO2 catalysts for CO oxidation were prepared by conventional incipient wetness impregnation followed by calcination at various temperatures. Their structures were char- acterized with X-ray diffraction （XRD）, laser Raman spectroscopy, X-ray photoelectron spectroscopy （XPS）, temperature-programmed reduction （TPR） and X-ray absorption fine structure （XAFS） spectroscopy. Both XRD and Raman spectroscopy only detect the existence of Co3O4 crystallites in all catalysts. However, XPS results indicate that excess Co2＋ ions are present on the surface of Co3O4 in Co3O4（200）/Si02 as compared with bulk Co3O4. Meanwhile, TPR results suggest the presence of surface oxygen vacancies on Co3O4 in Co3O4（200）/SiO2, and XAFS results demonstrate that Co3O4 in Co3O4（200）/SIO2 contains excess Co2＋. Increasing calcination temperature results in oxidation of excess Co2＋ and the decrease of the concentration of surface oxygen vacancies, consequently the for- mation of stoichiometric Co3O4 on supported catalysts. Among all Co3O4/SiO2 catalysts, Co3O4（200）/SiO2 exhibits the best catalytic performance towards CO oxidation, demonstrating that excess Co2＋ and surface oxygen vacancies can enhance the catalytic activity of Co3O4 towards CO oxidation. These results nicely demonstrate the effect of calcination temperature on the structure and catalytic performance towards CO oxidation of silicasupported Co3O4 catalysts and highlight the important role of surface oxygen vacancies on Co3O4.

XPS study of surface absorbed oxygen of ABO_3 mixed oxides

Perovskite-type complex oxides ABO3 （A=Sr, La; B=Mn, Fe, Co） were prepared by citric acid method. The degradation of water-solubilized dyes was carried out using the mixed oxides as photocatalyst. The surface absorbed oxygen was analyzed using X-ray photoelectron spectroscopy （XPS）. The results indicated that there was a relationship between the photocatalytic activity and the content of the surface absorbed oxygen. The higher the content of the surface absorbed oxygen was, the better the performance of the photocatalyst.

In-situ decoration of metallic Bi on BiOBr with exposed(110)facets and surface oxygen vacancy for enhanced solar light photocatalytic degradation of gaseous n-hexane

Photocatalytic degradation of gaseous pollutants on Bi-based semiconductors under solar lightirradiation has attracted significant attention.However,their application in gaseous straight-chainalkane purification is still rare.Here,a series of Bi/BiOBr composites were solvothermally synthe-sized and applied in solar-light-driven photocatalytic degradation of gaseous n-hexane.The charac-terization results revealed that both increasing number of functional groups of alcohol solvent(from methanol and ethylene glycol to glycerol)and solvothermal temperature(from 160 and 180to 200℃)facilitated the in-situ formation of metallic Bi nanospheres on BiOBr nanoplates withexposed(110)facets.Meanwhile,chemical bonding between Bi and BiOBr was observed on theseexposed facets that resulted in the formation of surface oxygen vacancy.Furthermore,the synergis-tic effect of optimum surface oxygen vacancy on exposed(110)facets led to a high visible light re-sponse,narrow band gap,great photocurrent,low recombination rate of the charge carriers,andstrong·O2-and h*formation,all of which resulted in the highest removal efficiency of 97.4%within120 min of 15 ppmv of n-hexane on Bi/BiOBr.Our findings efficiently broaden the application ofBi-based photocatalysis technology in the purification of gaseous straight-chain pollutants emittedby the petrochemical industry.

Effects of surface physicochemical properties on NH_3-SCR activity of MnO_2 catalysts with different crystal structures

α‐,β‐,δ‐,andγ‐MnO2nanocrystals are successfully prepared.We then evaluated the NH3selective catalytic reduction(SCR)performance of the MnO2catalysts with different phases.The NOx conversion efficiency decreased in the order:γ‐MnO2>α‐MnO2>δ‐MnO2>β‐MnO2.The NOx conversion with the use ofγ‐MnO2andα‐MnO2catalysts reached90%in the temperature range of140–200°C,while that based onβ‐MnO2reached only40%at200°C.Theγ‐MnO2andα‐MnO2nanowire crystal morphologies enabled good dispersion of the catalysts and resulted in a relatively high specific surface area.We found thatγ‐MnO2andα‐MnO2possessed stronger reducing abilities and more and stronger acidic sites than the other catalysts.In addition,more chemisorbed oxygen existed on the surface of theγ‐MnO2andα‐MnO2catalysts.Theγ‐MnO2andα‐MnO2catalysts showed excellent performance in the low‐temperature SCR of NO to N2with NH3.

Tuning surface active oxygen of lanthanum oxide via partial dissolution and regrowth of crystallites

A commercial lanthanum oxide was modified into X%-La2O3 samples via partial dissolution and regrowth of crystallites, wherein the X value denotes the weight percent of the initial metal oxide powder dissolved by nitric acid. BET measurements and TEM observations indicate that the 20%-La2O3 sample has an increased specific surface area, relatively thin and small crystallites in size. TPD/TPR profiles also show that the 20%-La2O3 sample has more surface active oxygen than the 0%-La2O3 sample. Among the four X%-La2O3 samples, the highest activity for methane oxidation was obtained over the 20%-La2O3 sample. Therefore, the present work proves that the method of partial dissolution and regrowth of crystallites are effective to modify surface property of lanthanum oxide.

Detailed Description of Pulse Isotopic Exchange Method for Analyzing Oxygen Surface Exchange Behavior on Oxide Ion Conductors

A novel pulse 18O-16O isotopic exchange (PIE) technique for measurement of the rate of oxygen surface exchange of oxide ion conductors was presented. The technique employs a continuous flow packed-bed micro-reactor loaded with the oxide powder. The isothermal response to an 18O-enriched pulse passing through the reactor, thereby maintaining chemical equilibrium, is measured by on-line mass spectrometry. Evaluation of the apparent exchange rate follows from the uptake of 18O by the oxide at given reactor residence time and surface area available for exchange. The developed PIE technique is rapid, simple and highly suitable for screening and systematic studies. No rapid heating/quenching steps are required to facilitate 18O tracer anneal or analysis, as in other commonly used techniques based upon oxygen isotopic exchange. Moreover, the relative distribution of the oxygen isotopologues 18O2, 16O18O, and 16O2 in the effluent pulse provides insight into the mechanism of the oxygen exchange reaction. The PIE technique has been demonstrated by measuring the exchange rate of selected oxides with enhanced oxide ionic conductivity in the range of 350?900 oC. Analysis of the experimental data in terms of a model with two consecutive, lumped steps for the isotopic exchange reaction shows that for mixed conductors Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) and La2NiO4+δ the reaction is limited by the apparent rate of dissociative adsorption of O2 molecules at the oxide surface. For yttria-stabilized zirconia (YSZ), a change-over takes place, from rate-limitations by oxygen incorporation below ∽800 oC to rate-limitations by O2 dissociative adsorption above this temperature. Good agreement is obtained with exchange rates reported for these materials in literature.

Enhancement of gaseous mercury(Hg^0) adsorption for the modified activated carbons by surface acid oxygen function groups

This article discussed the benzoic acid activated carbons which have changed the types and content of acid oxygen-function groups on the surface of activated carbons and their effect on the adsorption for Hg^0 in simulated flue gas at 140 ℃. These surface acid oxygen function groups were identified by Boehm titration, Fourier transformation infrared spectrum, temperature programmed desorption and X-ray photoelectron spectroscopy. It indicates that the carboxyl, lactone and phenolic were formed when the benzoic acid is loaded on the surface of activated carbons. Among the surface acid oxygen function groups, the carboxyl groups enhance the adsorption capacities of Hg^0 for activated carbons to a greater extent.

Synergically regulated silver species and surface oxygen on manganese oxide for promoted activity of formaldehyde oxidation

Formaldehyde(HCHO)is a common indoor pollutant that is detrimental to human health.Its efficient removal has become an urgent demand to reduce the public health risk.In this work,Ag-MnO_(x)-based catalysts were prepared and activated under different atmosphere(i.e.,air,hydrogen(H_(2))and carbon monoxide(CO))for efficient oxidation of HCHO.The catalyst activated with CO(Ag/Mn-CO)displayed the highest activity among the tested samples with 90% conversion at 100℃ under a gas space velocity of 75,000 mL/(g_(cat)·hr).Complementary characterizations demonstrate that CO reduction treatment resulted in synergically regulated content of surface oxygen on support to adsorb/activate HCHO and size of Ag particle to dissociate oxygen to oxidize the adsorbed HCHO.In contrast,other catalysts lack for either abundant surface oxygen species or metallic silver with the appropriate particle size,so that the integrate activity is limited by one specific reaction step.This study contributes to elucidating the mechanisms regulating the oxidation activity of Ag-based catalysts.

Zn‐doping mediated formation of oxygen vacancies in SnO2 with unique electronic structure for efficient and stable photocatalytic toluene degradation

To optimize the electronic structure of photocatalyst,a facile one‐step approach is developed for the simultaneous realization of Zn‐doping and surface oxygen vacancies(SOVs)formation on SnO_(2).The Zn‐doped SnO_(2)with abundant SOVs exhibits efficient and stable performance for photocatalytic degradation of toluene under both low and high relative humidity.Experimental and theoretical calculations results show that the synergistic effects of Zn‐doping and SOVs on SnO_(2)can considerably boost the charge transfer and separation efficiency.Utilizing the in situ DRIFTS and theoretical calculations methods,it is revealed that the benzene ring of toluene is opened at benzoic acid on the SnO_(2)surface and selectively at benzaldehyde on the Zn‐doped SnO_(2)surface.This implies that Zn‐doped SnO_(2)photocatalysts shorten the pathway of toluene degradation,and toxic intermediates can be significantly inhibited.This work could provide a promising and sustainable route for safe and efficient removal of aromatic VOCs with photocatalytic technology.

Relationship between oxygen species and activity/stability in heteroatom(Zr,Y)-doped cerium-based catalysts for catalytic decomposition of CH_3SH

CeO2,Ce1–xZrxO2,and Ce1–xYxO2–δ(x=0.25,0.50,0.75,and 1.00)have been rapidly synthesized to estimate their catalytic behavior in decomposing CH3SH.The role of oxygen vacancies,and the relationship between the oxygen species and catalytic properties of CeO2 and Zr‐doped and Y‐doped ceria‐based materials are investigated in detail.Combining the observed catalytic performance with the characterization results,it can be deemed that surface lattice oxygen plays a critical role in methanethiol catalytic conversion over cerium oxides.Ce0.75Zr0.25O2 shows higher catalytic activity for CH3SH decomposition due to the large amount of surface lattice oxygen,readily available oxygen species,and excellent redox properties.Ce0.75Y0.25O2–δdisplays better catalytic stability owing to the greater number of oxygen vacancies that would promote bulk lattice oxygen migration to the surface of the catalyst in order to replenish surface lattice oxygen.In addition,the results show that the difference in chemical valence between Ce and the heteroatoms would strongly influence the amount of surface lattice oxygen as well as the mobility of bulk‐phase oxygen in these catalysts,thus affecting their activity and stability.

Positively charged carbon electrocatalyst for enhanced power performance of L-ascorbic acid fuel cells

Carbon surface with large oxygen and carbon ratio(O/C) indicated an outstanding electro-catalytic activity toward L-ascorbic acid oxidation, compared to platinum group metals. However, interrelation of surface functional groups and its electro-catalytic activity is still unclear. In this paper, we prepared different levels of oxidized carbons by a simple acid treatment and investigated the correlation between the surface oxygen functional groups of acid-treated carbon and electro-catalytic activity in an electrooxidation of L-ascorbic acid. Positively charged carbon was demonstrated by lone pair electron of oxygen from valence band spectra study. It was revealed that the positively charged carbon, especially involved in carbonyl, showed enhanced the electro-catalytic activity through both better adsorption of negatively charged reactants and lowered LUMO by electronegativity of oxygen.

Fluorite Ce_(0.8)Sm_(0.2)O_(2-δ) porous layer coating to enhance the oxygen permeation behavior of a BaCo_(0.7)Fe_(0.2)Nb_(0.1)O_(3-δ) mixed conductor

Fluorite Ce0.8Sm0.2O2-δ（SDC） nanopowder with a crystallite size of 15 nm was synthesized by a co-precipitation method. An SDC porous layer was coated onto a BaCo0.7Fe0.2Nb0.1O3-δ（BCFN） mixed conductor to improve its oxygen transport behavior. The results show that the SDC-coated BCFN membrane exhibits a remarkably higher oxygen permeation flux（JO2） than the uncoated BCFN in the partial oxidation of coke oven gas（COG）. The maximum JO2 value of the SDC-coated BCFN is 18.28 mL ·min^-1·cm^-2 under a COG/air flux of 177 mL ·min^-1/353 mL ·min^-1 at 875℃ when the thickness of the BCFN membrane is 1 mm; this JO2 value is 23% higher than that of the uncoated BCFN membrane. This enhancement is likely because of the higher oxygen ionic conductivity of SDC, which supplies oxygen vacancies and accelerates oxygen exchange on the membrane/coating layer/gas three-phase boundary.

A novel Cu_(1.5)Mn_(1.5)O_(4)photothermal catalyst with boosted surface lattice oxygen activation for efficiently photothermal mineralization of toluene

Developing a novel photothermal catalyst for efficient mineralization of volatile organic compounds(VOCs)is of great significance to control air pollution.Herein,for the first-time,a spinel Cu_(1.5)Mn_(1.5)O_(4)nanomaterial with enhanced surface lattice oxygen activation was successfully obtained by a novel light-driven in situ reconstruction strategy from its precursor(CuMnO_(2))for efficient toluene mineralization.X-ray diffraction(XRD)and high-resolution transmission electron microscopy(HRTEM)analyses confirm that the CuMnO_(2)phase was converted into spinel Cu1.5Mn1.5O4 phase under full spectrum light irradiation.Ultraviolet–visible–near infrared ray(UV–vis–NIR)spectroscopy,X-ray photoelectron spectroscopy(XPS)analysis,and density functional theory(DFT)calculations determine that the strong near-infrared absorption ability and low dissociation energy of oxygen bond in Cu_(1.5)Mn_(1.5)O_(4)are beneficial to its surface lattice oxygen activation.Furthermore,O2-temperature programmed desorption(TPD)and in situ diffuse reflectance infrared transform spectroscopy(DRIFTS)further indicate that the surface lattice oxygen of the Cu_(1.5)Mn_(1.5)O_(4)is easily activated under light irradiation,which can promote ring opening of toluene.This research endows a new design of photothermal nanomaterial with enhanced lattice oxygen activation for deep oxidation of VOCs.

S-doped carbon aerogels/GO composites as oxygen reduction catalysts

Composites of carbon aerogel and graphite oxide（GO） were synthesized using a self-assembly method based on dispersive forces. Their surface was modified by treatment in hydrogen sulfide at 650 and800 ℃. The samples obtained were characterized by adsorption of nitrogen, TA-MS, XPS, potentiometric titration, and HRTEM and tested as catalysts for oxygen reduction reactions（ORR） in an alkaline medium.The synergistic effect of the composite（electrical conductivity, porosity and surface chemistry） leads to a good ORR catalytic activity. The onset potential for the composite of carbon aerogel heated at 800 ℃ is shifted to a more positive value and the number of electron transfer was 2e-at the potential 0.68 V versus RHE and it increased to 4e-with an increase in the negative values of the potential. An excellent tolerance to methanol crossover was also recorded.

Effect of CeO_2 on Crystal Structures and Catalytic Properties of the Mn_2O_3 Catalysts

The manganese-cerium complex oxide catalysts were prepared by coprecipitation.The crystal structures,the desorption properties of surface oxygen and reducibility of these catalysts were investigated by means of X-ray diffraction analysis (XRD),temperature-programmed desopotion-mass spectrography (TPD-MS) and temperature-programmed reduction (TPR).The crystal structure of Mn-O and Mn-Ce-O catalysts are bixbyite-Mn2O3 and γ-Mn2O3 respectively.The presence of CeO2 can not change the position of the feature peaks of Mn2O3 on the TPD or profiles,but can increase evidently the amount of the adsorbed surface oxygen,which are correlated with the catalytic activity for methanol oxidation.The activity of the catalyst is optimum when Mn/Ce atom ratio is 4:1.The presence of CeO2 brings a change of the reducibility,which reveals that there is an interaction between Mn2O3 and CeO2.

Enhancing oxidation reaction over Pt-MnO_(2) catalyst by activation of surface oxygen

Formaldehyde(HCHO) and carbon monoxide(CO) are both common air pollutants and hazardous to human body. It is imperative to develop the catalyst that is able to efficiently remove these pollutants. In this work, we activated Pt-MnO_(2)under different conditions for highly active oxidation of HCHO and CO, and the catalyst activated under CO displayed superior performance. A suite of complementary characterizations revealed that the catalyst activated with CO created the highly dispersed Pt nanoparticles to maintain a more positively charged state of Pt, which appropriately weakens the Mn-O bonding strength in the adjacent region of Pt for efficient supply of active oxygen during the reaction. Compared with other catalysts activated under different conditions, the CO-activated Pt-MnO_(2)displays much higher activity for oxidation of HCHO and CO. This research contributes to elucidating the mechanism for regulating the oxidation activity of Pt-based catalyst.

Engineering surface oxygen vacancy of mesoporous CeO_(2) nanosheets assembled microspheres for boosting solar-driven photocatalytic performance

Surface oxygen vacancy defects of mesoporous CeO_(2)nanosheets assembled microspheres(D-CeO_(2))are engineered by polymer precipitation,hydrothermal and surface hydrogenation strategies.The resultant D-CeO_(2)with a main pore diameter of 9.3 nm has a large specific surface area(~102.3 m^(2)/g)and high thermal stability.The mesoporous nanosheets assembled microsphere structure prevents the nanosheets from aggregation,which is beneficial to effective mass transfer and shortens the migration distance of charge carriers.After surface hydrogenation,the photoresponse extends to long wavelength region,combing with the band gap from 2.63 eV reduced to 2.39 eV.Under AM 1.5 G radiation,the photocatalytic degradation rate of tetracycline(TC)can be up to 99.99%,which is three times as high as that of pristine CeO_(2)microspheres.The excellent solar-driven photocatalytic performance can be attributed to the efficient surface oxygen vacancy engineering and the mesoporous nanosheets assembled microsphere structure,which narrows the band gap,shortens the migration distance of carriers,promotes the spatial separation of photogenerated electron-hole pairs and favors mass transfer.The strategy provides new insights for fabricating other high-efficient oxide photocatalysts.

Enhanced CO catalytic oxidation by Sr reconstruction on the surface of LaxSr1-xCoO3-δ

Surface electronic structure of solid materials plays a critical role in heterogeneous catalysis. However, surface chemical composition of the perovskite oxides is usually dominated by segregated A-site cations and the amount of oxygen vacancies is relatively low, which seriously restricts their catalytic oxidation property. Here, we prepare perovskite LaxSrl xCO03 ~ （x = 0.3, 0.5, 0.7） with different Sr doping amount and experiment results show that perovskite LSCO with higher content of surface Sr possesses more oxy- gen vacancies and better catalytic activity. On this basis, we develop a new experimental strategy to cre- ate more surface oxygen vacancies to promote their CO catalytic activity. In this method, we use high active hydrogen atoms （BHa-） as reductant to realize surface in-situ chemical composite modification of LaxSrl xCo03 ~s （x = 0.3, 0.5, 0.7）, which causes their surface reconstruction （surface Sr enrichment）. The regulation mainly focuses on the atomic layer level without damaging their bulk phase structure. Different from traditional high temperature annealing under reducing atmosphere, this method is high-efficiency, green and controllable. Furthermore, we study the surface reconstruction process and demonstrated that it is atomic layer engineering on the surface of LaxSr1-xCoO3-δ （x = 0.3, 0.5, 0.7） by X-ray photoelectron spectroscopy （XPS） and X-ray absorption fine structure （XAFS）. Our experiment results also show that these samples treated by this method exhibit superior activity for CO oxidation compared with original samples.

Oxygen vacancy O-terminated surface:The most exposed surface of hexagonal WO3(001)surface

It is known that exposed surface determines material’s performance.WO3 is widely used in gas sensing and its working surface is proposed to control its sensitivity.However,the working surface,or most exposed surface with detailed surface structure remain unclear.In this paper,DFT calculation confirmed that oxygen vacancy O-terminated surface is the most exposed hexagonal WO3(001)surface,judging from competitive adsorption of CO and O2,working surface determination for CO sensing and comparison of oxygen vacancy formation ene rgies on different h-WO3(001)surfaces.It is found that DFT can be a useful alternate for exposed surface determination.Our results provide new perspectives and performance explanations for material research.