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Showing papers on "Oxygen published in 2018"


Journal ArticleDOI
01 Feb 2018
TL;DR: In this article, a facile and general approach to catalyst development via surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity for H2O2 production by electrochemical oxygen reduction was demonstrated.
Abstract: Hydrogen peroxide (H2O2) is a valuable chemical with a wide range of applications, but the current industrial synthesis of H2O2 involves an energy-intensive anthraquinone process. The electrochemical synthesis of H2O2 from oxygen reduction offers an alternative route for on-site applications; the efficiency of this process depends greatly on identifying cost-effective catalysts with high activity and selectivity. Here, we demonstrate a facile and general approach to catalyst development via the surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity (~90%) for H2O2 production by electrochemical oxygen reduction. We find that both the activity and selectivity are positively correlated with the oxygen content of the catalysts. The density functional theory calculations demonstrate that the carbon atoms adjacent to several oxygen functional groups (–COOH and C–O–C) are the active sites for oxygen reduction reaction via the two-electron pathway, which are further supported by a series of control experiments. The direct synthesis of hydrogen peroxide via oxygen reduction is an attractive alternative to the anthraquinone process. Here, a general trend linking oxygenation of carbon surfaces with electrocatalytic performance in peroxide synthesis is demonstrated, and computational studies provide further insight into the nature of the active sites.

967 citations


Journal ArticleDOI
TL;DR: Systematic studies reveal that the excellent PEC activity should be attributed to their ultrathin crystalline structure and abundant oxygen vacancies, which could effectively facilitate the hole transport/trapping and provide more active sites for water oxidation.
Abstract: Photoelectrochemical (PEC) water splitting is a promising method for storing solar energy in the form of hydrogen fuel, but it is greatly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, a facile solution impregnation method is developed for growing ultrathin (2 nm) highly crystalline β-FeOOH nanolayers with abundant oxygen vacancies on BiVO4 photoanodes. These exhibited a remarkable photocurrent density of 4.3 mA cm-2 at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G), which is approximately two times higher than that of amorphous FeOOH fabricated by electrodeposition. Systematic studies reveal that the excellent PEC activity should be attributed to their ultrathin crystalline structure and abundant oxygen vacancies, which could effectively facilitate the hole transport/trapping and provide more active sites for water oxidation.

512 citations


Journal ArticleDOI
TL;DR: In this paper, a ligand-assisted polyol reduction method was used to synthesize porous cobalt oxide nanoplates enriched with oxygen vacancies, which enabled large-scale synthesis that offers superior uniformity, solution dispersity and controllable concentration of oxygen vacancies on surface.

399 citations


Journal ArticleDOI
Yaowen Gao1, Yue Zhu1, Lai Lyu1, Qingyi Zeng1, Xueci Xing1, Chun Hu1 
TL;DR: These findings not only propose a novel PMS activation mechanism in terms of simultaneous PMS oxidation and reduction for the production of nonradical and radical species but also provide a valuable insight for the development of efficient metal-free catalysts through nonmetal doping toward the persulfate-based environmental cleanup.
Abstract: Oxygen-doped graphitic carbon nitride (O-CN) was fabricated via a facile thermal polymerization method using urea and oxalic acid dihydrate as the graphitic carbon nitride precursor and oxygen source, respectively. Experimental and theoretical results revealed that oxygen doping preferentially occurred on the two-coordinated nitrogen positions, which create the formation of low and high electron density areas resulting in the electronic structure modulation of O-CN. As a result, the resultant O-CN exhibits enhanced catalytic activity and excellent long-term stability for peroxymonosulfate (PMS) activation toward the degradation of organic pollutants. The O-CN with modulated electronic structure enables PMS oxidation over the electron-deficient C atoms for the generation of singlet oxygen (1O2) and PMS reduction around the electron-rich O dopants for the formation of hydroxyl radical (•OH) and sulfate radical (SO4•-), in which 1O2 is the major reactive oxygen species, contributing to the selective reactivity of the O-CN/PMS system. Our findings not only propose a novel PMS activation mechanism in terms of simultaneous PMS oxidation and reduction for the production of nonradical and radical species but also provide a valuable insight for the development of efficient metal-free catalysts through nonmetal doping toward the persulfate-based environmental cleanup.

395 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed oxygen-enriched carbon nitride polymer (OCN) models, which were proven to more easily produce 1,4-endoperoxide species and have a high selectivity for molecular oxygen reduction to H2O2, rather than superoxide radicals, through theoretical calculations and experiments.
Abstract: H2O2 is a green, environmentally friendly potential energy source. The photocatalytic reduction of molecular oxygen to synthesise H2O2 is an eco-friendly strategy compared with the anthraquinone method and H2/O2 direct synthesis. We proposed oxygen-enriched carbon nitride polymer (OCN) models, which were proven to more easily produce 1,4-endoperoxide species and have a high selectivity for molecular oxygen reduction to H2O2, rather than superoxide radicals, through theoretical calculations and experiments. The apparent quantum yield for H2O2 production by OCNs reached 10.2% at 420 nm under an O2 atmosphere, which was 3.5 times higher than that of g-C3N4 and the activity did not decay over 20 h. OCN has a better oxygen reducibility and electron–hole separation efficiency than g-C3N4 and is more prone to 2-electron reduction in the ORR. This work promotes understanding of the mechanism of photocatalytic oxygen reduction and provides a new idea for the design and synthesis of new materials for the preparation of H2O2.

383 citations


Journal ArticleDOI
TL;DR: Na2/3[Mg0.28Mn0.72]O2 exhibits an excess capacity and it is shown that this is caused by oxygen redox, even though Mg2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygenRedox.
Abstract: The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li+-O(2p)-Li+ interactions). Na2/3[Mg0.28Mn0.72]O2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg2+ remains in Na2/3[Mg0.28Mn0.72]O2, which stabilizes oxygen.

367 citations


Journal ArticleDOI
TL;DR: In this paper, a series of MnOx-CeO2 catalysts with various Mn/(Mn+Ce) molar ratios were synthesized with citric acid complex method for O-vacancy study in soot catalytic combustion.
Abstract: Oxygen vacancy (O-vacancy) is essential in catalytic oxidation but little is known about its insight. Herein, a series of MnOx-CeO2 catalysts with various Mn/(Mn + Ce) molar ratios were synthesized with citric acid complex method for O-vacancy study in soot catalytic combustion. The samples were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, O2-temperature programmed desorption (O2-TPD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy. It has been shown that MnOx(0.4)-CeO2 catalyst presented more O-vacancies, thus exhibiting the highest catalytic activities and redox properties. With the utilization of in situ Raman, two types of O-vacancies, including Frenkel-type oxygen vacancy (F OV) and intrinsic oxygen vacancy (I OV), were clarified. Furthermore, the transform relation between F OV and I OV was found. Those two types of O-vacancies favored to the migration and transformation of active species, enhancing further the oxidation-reduction cycle and the catalytic activity for soot oxidation. In addition, Mn4+/Mn3+(Mn2+), Olatt, Osur and Ce4+/Ce3+ were believed to play important roles in soot oxidation. Finally, evolution of O-vacancies was proposed, which is of significance for soot catalytic oxidation.

355 citations


Journal ArticleDOI
01 Oct 2018
TL;DR: In this paper, the local geometric ligand environment and electronic metal states of oxygen-coordinated iridium centres in nickel-leached IrNi@IrOx metal oxide core-shell nanoparticles under catalytic oxygen evolution conditions were investigated.
Abstract: The electro-oxidation of water to oxygen is expected to play a major role in the development of future electrochemical energy conversion and storage technologies. However, the slow rate of the oxygen evolution reaction remains a key challenge that requires fundamental understanding to facilitate the design of more active and stable electrocatalysts. Here, we probe the local geometric ligand environment and electronic metal states of oxygen-coordinated iridium centres in nickel-leached IrNi@IrOx metal oxide core–shell nanoparticles under catalytic oxygen evolution conditions using operando X-ray absorption spectroscopy, resonant high-energy X-ray diffraction and differential atomic pair correlation analysis. Nickel leaching during catalyst activation generates lattice vacancies, which in turn produce uniquely shortened Ir–O metal ligand bonds and an unusually large number of d-band holes in the iridium oxide shell. Density functional theory calculations show that this increase in the formal iridium oxidation state drives the formation of holes on the oxygen ligands in direct proximity to lattice vacancies. We argue that their electrophilic character renders these oxygen ligands susceptible to nucleophilic acid–base-type O–O bond formation at reduced kinetic barriers, resulting in strongly enhanced reactivities. The precise understanding of the active phase under reaction conditions at the molecular level is crucial for the design of improved catalysts. Now, Strasser, Jones and colleagues correlate the high activity of IrNi@IrOx core–shell nanoparticles with the amount of lattice vacancies produced by the nickel leaching process that takes place before and during water oxidation, and elucidate the underlying structural-electronic effects.

350 citations


Journal ArticleDOI
TL;DR: In this paper, single-atom-level structural investigations reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS2 single layers during ambient exposure, leading to solid-solution-type 2D MoS 2-xOx crystals.
Abstract: The chemical inertness of the defect-free basal plane confers environmental stability to MoS2 single layers, but it also limits their chemical versatility and catalytic activity The stability of pristine MoS2 basal plane against oxidation under ambient conditions is a widely accepted assumption however, here we report single-atom-level structural investigations that reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS2 single layers during ambient exposure The use of scanning tunnelling microscopy reveals a slow oxygen-substitution reaction, during which individual sulfur atoms are replaced one by one by oxygen, giving rise to solid-solution-type 2D MoS2-xOx crystals Oxygen substitution sites present all over the basal plane act as single-atom reaction centres, substantially increasing the catalytic activity of the entire MoS2 basal plane for the electrochemical H2 evolution reaction

255 citations


Journal ArticleDOI
TL;DR: The distinctive anionic oxygen activity of battery electrodes with different transition metals is revealed by elucidating the effect of the transition metal on oxygen redox activity by combining X-ray spectroscopy and operando differential electrochemical mass spectrometry.
Abstract: Recent research has explored combining conventional transition-metal redox with anionic lattice oxygen redox as a new and exciting direction to search for high-capacity lithium-ion cathodes. Here, we probe the poorly understood electrochemical activity of anionic oxygen from a material perspective by elucidating the effect of the transition metal on oxygen redox activity. We study two lithium-rich layered oxides, specifically lithium nickel metal oxides where metal is either manganese or ruthenium, which possess a similar structure and discharge characteristics, but exhibit distinctly different charge profiles. By combining X-ray spectroscopy with operando differential electrochemical mass spectrometry, we reveal completely different oxygen redox activity in each material, likely resulting from the different interaction between the lattice oxygen and transition metals. This work provides additional insights into the complex mechanism of oxygen redox and development of advanced high-capacity lithium-ion cathodes.

245 citations


Journal ArticleDOI
TL;DR: In this paper, the authors obtained NiFe-based catalysts with appropriate electronic conductivity and catalytic activity through introduction of oxygen vacancies by a facile and economic NaBH4 reduction approach.
Abstract: Advanced electrocatalysts toward oxygen evolution reaction (OER) at high current density with low overpotential remain a significant challenge for electrochemical water splitting. Herein, NiFe-based catalysts with appropriate electronic conductivity and catalytic activity have been obtained through introduction of oxygen vacancies by a facile and economic NaBH4 reduction approach. The combined density functional theory calculations, physical characterization, and electrochemical studies disclose that the reductive treatment creates a high amount of oxygen vacancies, high active sites, and a low energy barrier for OER. The oxygen vacancy-rich catalyst yields a more than 2-fold increased current density (from 100 to 240 mA cm–2) at a low overpotential of 270 mV, accompanied by good stability under OER conditions. The approach is also broadly applicable for NiFe compounds synthesized via different methods or substrates.

Journal ArticleDOI
TL;DR: In this article, a new type of hybrid of transition metal phosphides (TMPs) and defective carbon nanoparticles (CoP-DC) was constructed, and the interfacial charge redistribution was observed, which contributed to enhanced ORR activity on the defective carbon and enhanced oxygen evolution reaction (OER) on the CoP.
Abstract: DOI: 10.1002/aenm.201703623 ideal performance toward ORR or OER, the high price, scarcity, and instability still hampers their large-scale generalization. At present, developing efficient and nonnoble-metal catalysts has attracted extensive interest.[11–18] For ORR, defective carbon-based materials, typically heteroatom-doped carbon, are extensively demonstrated as efficient electrocatalysts.[19–22] For OER, in addition to common transition metal oxides or (oxy)hydroxides, transition metal phosphides (TMPs) have achieved considerable research and development attention due to superior performance.[23–27] In this regard, the composites of the TMPs and defective carbon are considered as promising candidates for both ORR and OER. More recently, some works reported that the composites of the TMPs and defective carbon compared to the single component displayed enhanced catalytic performance, which was probably attributed to the increased electronic conductivity due to the introduction of conductive carbon.[28–30] However, the promoting factor was not well understood. For the composites, undoubtedly, the interfacial properties, especially the interfacial charge states, are important parameters that could influence the catalytic performance.[31,32] Therefore, in order to overcome high catalytic reaction barrier, designing the hybrids of the TMPs and defective carbon and probing the interfacial charge distribution behavior are highly desirable to realize bifunctional oxygen electrocatalysis. Herein, we constructed a new type of hybrids of the CoP and defective carbon (marked as CoP–DC). We revealed the interfacial charge transfer process of the hybrids by multiple synchrotron-based X-ray absorption structure, ultraviolet photoelectron spectra (UPS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The interfacial charge redistribution was observed, which subsequently contributed to enhanced ORR activity on the defective carbon and enhanced OER activity on the CoP. The CoP–DC hybrids were synthesized through a simple phosphorization reaction toward the Co2+-contained polymer hydrogel. Typically, the polymer hydrogel was obtained by inserting Co2+ into polymer hydrogel framework under alkaline condition according to previous reports, and then was phosphorized The development of efficient catalysts for both oxygen reduction and evolution reactions (oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)) is central to regenerative fuel cells and rechargeable metal– air batteries. It is highly desirable to achieve the efficient integration of dual active components into the catalysts and to understand the interaction between the dual components. Here, a facile approach is demonstrated to construct defective carbon–CoP nanoparticle hybrids as bifunctional oxygen electrocatalysts, and further probe the interfacial charge distribution behavior. By combining multiple synchrotron-based X-ray spectroscopic characterizations with density functional theory calculations, the interfacial charge polarization with the electrons gathering at the defective carbon surface and the holes gathering at the CoP surface due to strong interfacial coupling is revealed, which simultaneously facilitates the ORR and OER with remarkable bifunctional oxygen electrode activities. This work not only offers a bifunctional oxygen catalyst with outstanding performance, but also unravels the promoting factor of the hybrids from the view of interfacial charge distribution.

Journal ArticleDOI
TL;DR: It is confirmed that Ce-γ-MnO2 exhibited more surface oxygen vacancies and surface defects, which play a key role during the decomposition of ozone, indicating that it is a promising material for ozone decomposition.
Abstract: Transition metal (cerium and cobalt) doped γ-MnO2 (M-γ-MnO2, where M represents Ce, Co) catalysts were successfully synthesized and characterized. Cerium-doped γ-MnO2 materials showed ozone (O3) conversion of 96% for 40 ppm of O3 under relative humidity (RH) of 65% and space velocity of 840 L g–1 h–1 after 6 h at room temperature, which is far superior to the performance of the Co-γ-MnO2 (55%) and γ-MnO2 (38%) catalysts. Under space velocity of 840 L g–1 h–1, the conversion of ozone over the Ce-γ-MnO2 catalyst under RH = 65% and dry conditions within 96 h was 60% and 100%, respectively, indicating that it is a promising material for ozone decomposition. XRD and HRTEM data suggested that Ce-γ-MnO2 formed mixed crystals consisting of α-MnO2 and γ-MnO2 with specific surface area increased from 74 m2/g to 120 m2/g compared to undoped γ-MnO2, thus more surface defects were introduced. H2-TPR, O2-TPD, XPS, Raman, and EXAFS confirmed that Ce-γ-MnO2 exhibited more surface oxygen vacancies and surface defects, whi...

Journal ArticleDOI
TL;DR: In this paper, the authors systematically analyzed the reasons for the increase of the capacity that promoted by oxygen functional groups in charge∕discharge cycling tests and the mechanism how the pseudocapacitance is provided by the oxygen functional group in the acid/alkaline aqueous electrolyte.

Journal ArticleDOI
TL;DR: A high-performance oxygen electrocatalyst based on a triple perovskite, Nd 1.5Ba1.5CoFeMnO9−δ (NBCFM), which shows superior activity and durability for oxygen electrode reactions to single and double perovSKites, and is the best activity reported to date.
Abstract: Highly active and durable bifunctional oxygen electrocatalysts have been of pivotal importance for renewable energy conversion and storage devices, such as unitized regenerative fuel cells and metal-air batteries. Perovskite-based oxygen electrocatalysts have emerged as promising nonprecious metal bifunctional electrocatalysts, yet their catalytic activity and stability still remain to be improved. We report a high-performance oxygen electrocatalyst based on a triple perovskite, Nd1.5Ba1.5CoFeMnO9-δ (NBCFM), which shows superior activity and durability for oxygen electrode reactions to single and double perovskites. When hybridized with nitrogen-doped reduced graphene oxide (N-rGO), the resulting NBCFM/N-rGO catalyst shows further boosted bifunctional oxygen electrode activity (0.698 V), which surpasses that of Pt/C (0.801 V) and Ir/C (0.769 V) catalysts and which, among the perovskite-based electrocatalysts, is the best activity reported to date. The superior catalytic performances of NBCFM could be correlated to its oxygen defect-rich structure, lower charge transfer resistance, and smaller hybridization strength between O 2p and Co 3d orbitals.

Journal ArticleDOI
16 May 2018-Joule
TL;DR: In this article, a multi-phase catalyst coating (∼30nm thick), composed of BaCoO 3−x (BCO) and PrCoO3−x nanoparticles (NPs) and a conformal PrBa 0.2 Co 2 O 5+δ (PBCC) thin film, has dramatically enhanced the rate of oxygen reduction reaction (ORR).


Journal ArticleDOI
TL;DR: In this paper, the critical role of oxygen vacancies in photocatalytic water oxidation was investigated using a one-step hydrothermal method with in-situ reducing treatment.
Abstract: Photocatalytic water oxidation suffers from sluggish kinetics and remains the bottleneck for water splitting. Here, using CeO 2 nanorods as model photocatalyst we studied the critical role of oxygen vacancies in photocatalytic water oxidation. First CeO 2 nanorods with similar morphology but different concentration of oxygen vacancies were fabricated by one-step hydrothermal method with in-situ reducing treatment. The optical absorption, charge transfer efficiency, and photocatalytic activity in oxygen generation were found closely dependent on the concentration of oxygen vacancies. Then density functional theory calculations were conducted to unveil the role of oxygen vacancies and understand the water oxidation mechanism. It was found the presence of oxygen vacancies narrows the bandgap and modulates the electronic structure for accelerating the charge transfer, in good agreement with the experimental observations. The overall oxygen generation pathway was screened and the oxygen vacancies were found to lower the barrier energy for the rate limiting step of O O bond formation and restrain the reverse reaction of O and H, thus the O 2 generation kinetics on oxygen-defective CeO 2 are improved significantly. This study provides in-depth understanding on the critical role of oxygen vacancies in photocatalytic water oxidation and is helpful for designing highly efficient photocatalyst to overcome the bottleneck of water splitting.


Journal ArticleDOI
TL;DR: In this paper, the authors tailor the quantity and distribution of oxygen vacancies, as one of typical defects, on surface or bulk of thermal-treated WO3 in the different H2 concentration.
Abstract: Defect engineering is a promising strategy to enhance light absorption and charge separation of photocatalysts. Herein, we simply tailor the quantity and distribution of oxygen vacancies, as one of typical defects, on surface or bulk of thermal-treated WO3 in the different H2 concentration. The quantity of bulk oxygen vacancies on WO3 consistently rises with the increased H2 concentration, while that of surface oxygen vacancies presents a volcano-type variation. The sample of WO3-H20, thermal-pretreated in 20% H2, contains the largest amount of surface oxygen vacancies. Our results show that both surface and bulk oxygen vacancies on WO3 can promote the visible light photocatalytic activity in water splitting, however, in different ways. Bulk oxygen vacancies mainly promote the visible light harvesting and slightly restrain the electrons and holes recombination by narrowing band gap energy (Eg), while surface oxygen vacancies significantly increase the charge-carriers separation efficiency by lowering valence band edge (VBE). Compared with the light absorption, the separation of electrons and holes is more critical in photocatalytic oxygen evolution over WO3, revealing the more decisive role of surface oxygen vacancies than bulk oxygen vacancies. Expectedly, WO3-H20 shows the highest charge-carriers separation efficiency and visible light photocatalytic performance. Our work provides a new insight into designing of efficient defect-engineered semiconductors for the related solar light utilization processes.

Journal ArticleDOI
TL;DR: A simple chemical deposition method for controllable synthesis of defective anatase TiO2 nanocrystals under various calcination atmospheres is reported, showing the critical role of VO with a suitable concentration in transferring photogenerated charges.
Abstract: The status of defects of TiO2 are of fundamental importance in determining its physicochemical properties. Here we report a simple chemical deposition method for controllable synthesis of defective anatase TiO2 nanocrystals under various calcination atmospheres. XPS and ESR analysis reveals that both the oxygen vacancies ( VO) and the trivalent titanium (Ti3+) defects exist in TiO2 after N2 treatment (N-TiO2). Meanwhile, mainly VO defects can be obtained in TiO2 with air calcination (A-TiO2). ESR spectra for reactive oxygen species determination, clearly show that the visible light catalytic activity is mainly caused by the efficient activation of oxygen molecules to •O2- species for A-TiO2, which play an important role in hindering the accumulation of intermediates during p-chlorophenol (4-CP) photodegradation process. However, the oxygen molecules cannot be activated for N-TiO2 even with superior visible light absorption and thus the photogenerated electron are reductant, which participated in the transformation of BQ to HQ via electron shuttle mechanism. Moreover, A-TiO2 exhibits higher separation efficiency of photogenerated carriers than that of N-TiO2, showing the critical role of VO with a suitable concentration in transferring photogenerated charges.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional (2D) iron-cobalt oxide (Fe1Co1Ox-origin) was treated with hydrogenation to tune its oxygen vacancy density.
Abstract: The oxygen evolution reaction (OER) represents the rate-determining step of electrocatalytic water splitting into hydrogen and oxygen. Creating oxygen vacancies and adjusting their density has proven to be an effective strategy to design high-performance OER catalysts. Herein, a hydrogenation method is applied to treat a two-dimensional (2D) iron-cobalt oxide (Fe1Co1Ox-origin), with the purpose of tuning its oxygen vacancy density. Notably, compared with Fe1Co1Ox-origin, the iron-cobalt oxide hydrogenated at 200 °C and 2.0 MPa optimized conditions exhibits a markedly improved OER activity in 1.0 M KOH (with an overpotential η of 225 mV at a current density of 10 mA·cm–2) and a rapid reaction kinetics (with a Tafel slope of 36.0 mV·dec–1). Moreover, the OER mass activity of the hydrogenated oxide is 1.9 times that of Fe1Co1Ox-origin at an overpotential of 350 mV. The experimental results, combined with density functional theory (DFT) calculations, reveal that the optimal control of oxygen vacancies in 2D Fe1Co1Ox via hydrogenation can improve the electronic conductivity and promote OH– adsorption onto nearby low-coordinated Co3+ sites, resulting in a significantly enhanced OER activity.

Journal ArticleDOI
TL;DR: This work demonstrates that Ruddlesden–Popper materials can be utilized as active catalysts for oxygen evolution through rational design of structural and electronic configurations that are unattainable in many other crystalline metal oxide phases.
Abstract: The electrolysis of water is of global importance to store renewable energy and the methodical design of next-generation oxygen evolution catalysts requires a greater understanding of the structural and electronic contributions that give rise to increased activities. Herein, we report a series of Ruddlesden–Popper La0.5Sr1.5Ni1−xFexO4±δ oxides that promote charge transfer via cross-gap hybridization to enhance electrocatalytic water splitting. Using selective substitution of lanthanum with strontium and nickel with iron to tune the extent to which transition metal and oxygen valence bands hybridize, we demonstrate remarkable catalytic activity of 10 mA cm−2 at a 360 mV overpotential and mass activity of 1930 mA mg−1ox at 1.63 V via a mechanism that utilizes lattice oxygen. This work demonstrates that Ruddlesden–Popper materials can be utilized as active catalysts for oxygen evolution through rational design of structural and electronic configurations that are unattainable in many other crystalline metal oxide phases.

Journal ArticleDOI
TL;DR: In this paper, surface species and oxygen vacancies were studied in MnO x (0.4)-CeO 2 catalysts for repeated soot oxidation in a 10% O 2 /Ar gas flow and showed favorable activity and satisfactory durability.
Abstract: Surface species and oxygen vacancies were studied in MnO x (0.4)-CeO 2 toward repeated soot oxidation. MnO x (0.4)-CeO 2 catalysts prepared by the citric acid complex method were repeatedly used in a 10% O 2 /Ar gas flow and showed favorable activity and satisfactory durability toward soot oxidation. X-ray diffraction (XRD), N 2 adsorption/desorption, Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and in situ visible/UV Raman characterization methods were utilized to investigate the structural features of fresh and reused catalysts. The irreversible conversion of high valence manganese species as well as the reduction of Frenkel-type oxygen vacancies and lattice oxygen could be clearly observed in the reused samples, which were associated with the slight deactivation. Spectators and participators were two existing forms of Frenkel-type oxygen vacancies. It was noteworthy that the participators almost fully regenerated after each reaction cycle, which ensured the ability to activate O latt in repeated soot oxidation process. Therefore, the catalysts maintained favorable activity and satisfactory durability, which was mainly because the relatively stable level of participators.

Journal ArticleDOI
TL;DR: The performance of the catalyst has been improved because the abundant active oxygen vacancies are fabricated by the electrostatic interaction between oxygen atoms inside the tunnels and the introduced K+, which offers a new perspective to design a high efficiency catalyst and may promote manganese oxide for practical ozone elimination.
Abstract: α-MnO2 is a promising material for ozone catalytic decomposition and the oxygen vacancy is often regarded as the active site for ozone adsorption and decomposition. Here, α-MnO2 nanowire with tunable K+ concentration was prepared through a hydrothermal process in KOH solution. High concentration K+ in the tunnel can expand crystal cell and break the charge balance, leading to a lower average oxidation state (AOS) of Mn, which means abundant oxygen vacancy. DFT calculation has also proven that the samples with higher K+ concentration exhibit lower formation energy for oxygen vacancy. Due to the enormous active oxygen vacancies existing in the α-MnO2 nanowire, the lifetime of the catalyst (corresponding to 100% ozone removal rate, 25 °C) is increased from 3 to 15 h. The FT-IR results confirmed that the accumulation of intermediate oxygen species on the catalyst surface is the main reason why it is deactivated after long time reaction. In this work, the performance of the catalyst has been improved because t...

Journal ArticleDOI
TL;DR: A series of iridium(III) complexes in which limited internal conversion between two excited states results in dual phosphorescence from two different excited states upon excitation at a single wavelength are reported, the first example of using a molecular probe for simultaneous bioimaging of hypoxia and hyperoxia.
Abstract: Hypoxia and hyperoxia, referring to states of biological tissues in which oxygen supply is in sufficient and excessive, respectively, are often pathological conditions. Many luminescent oxygen probes have been developed for imaging intracellular and in vivo hypoxia, but their sensitivity toward hyperoxia becomes very low. Here we report a series of iridium(III) complexes in which limited internal conversion between two excited states results in dual phosphorescence from two different excited states upon excitation at a single wavelength. Structural manipulation of the complexes allows rational tuning of the dual-phosphorescence properties and the spectral profile response of the complexes toward oxygen. By manipulating the efficiency of internal conversion between the two emissive states, we obtained a complex exhibiting naked-eye distinguishable green, orange, and red emission in aqueous buffer solution under an atmosphere of N2, air, and O2, respectively. This complex is used for intracellular and in vivo oxygen sensing not only in the hypoxic region but also in normoxic and hyperoxic intervals. To the best of our knowledge, this is the first example of using a molecular probe for simultaneous bioimaging of hypoxia and hyperoxia.

Journal ArticleDOI
TL;DR: In this article, the consequences of exposing halide perovskites to an oxygen-containing atmosphere, in particular methylammonium lead iodide, was systematically investigated.
Abstract: We systematically investigate the consequences of exposing halide perovskites to an oxygen-containing atmosphere, in particular methylammonium lead iodide, the archetypal compound used as photo-absorber in perovskite solar cells. For this purpose, we study oxygen solubility and global reaction with oxygen both in the dark and under light, and we refer to the kinetics in terms of surface reaction and bulk diffusion. As thermodynamics reveals, the material is unstable against oxygen, primarily because of the large driving force of water formation. While under light the material quickly degrades, in the dark the surface reaction kinetics – not the bulk transport – is very sluggish and keeps it metastable. For the same reason, oxygen incorporation into the lattice is negligible in the dark. On illumination, an accelerated oxygen in-diffusion occurs (as shown by 18O incorporation experiments) that severely modifies the electronic and ionic conductivities in the way that is expected for an acceptor dopant. Lastly, we investigate the impact of cation as well as anion mixing on the degradation and stress the necessity of using encapsulation during solar cell operation.

Journal ArticleDOI
Na Huang1, Zhenping Qu1, C. Dong1, Yuan Qin1, Xiaoxiao Duan1 
TL;DR: In this article, a nanosized MnO 2 catalysts with α-, β- and hierarchically α@β-crystal phases were synthesized, and the catalytic activity was strongly related with the ratio of α-MnO 2 and β-mNO 2.
Abstract: The crystalline phase of manganese dioxide catalysts shows strong influence on its catalytic performance, and the construction of hierarchically nanostructured materials with active interface and oxygen vacancy is an effective approach to develop the enhanced functionality. Herein, nanosized MnO 2 catalysts with α-, β- and hierarchically α@β-crystal phases were synthesized. α@β-MnO 2 catalysts showed the excellent activity than pure MnO 2 in toluene combustion, either α-MnO 2 or β-MnO 2. The catalytic activity was strongly related with the ratio of α-MnO 2 and β-MnO 2 in α@β-MnO 2 catalyst, and α@β-MnO 2 (1:1) exhibited the highest activity for toluene oxidation and toluene can be completely oxidized to CO 2 and H 2 O at about 205 °C with a space velocity (GSHV) of 30,000 h −1 . HRTEM, Raman and XPS demonstrated that α@β-MnO 2 owned the abundant defects due to the mixed phase interfacial structure. The strong synergistic effect in α@β-MnO 2 catalyst with larger specific area enhanced and facilitated the adsorption and activation of toluene molecules and oxygen species. The mobility of oxygen species and low-temperature reducibility compared with pure MnO 2 were significantly enhanced. When the ratio of α-MnO 2 and β-MnO 2 was 1:1, α@β-MnO 2 reached the maximum biphase interface content, formed large amount of oxygen vacancy, and showed the strongest synergistic effect and activation ability for reactants. Thus it was thought that the formation of the special biphase structure of α@β-MnO 2 was beneficial to the improvement of toluene catalytic oxidation activity.

Journal ArticleDOI
TL;DR: In this article, a hierarchical tubular assembly of metal nitride nanosheets via a facile hyperedge was proposed for fuel cells with high energy efficiency and low cost.
Abstract: Highly stable and efficient oxygen electrocatalyst with low cost is of prime significance for fuel cells. Herein, we report hierarchical tubular assembly of metal nitride nanosheets via a facile hy...

Journal ArticleDOI
TL;DR: A remarkable enhancement in oxygen reduction reaction (ORR) activity of NiCo2O4 supported on hollow carbon spheres (HCS) achieved through generating abundant oxygen vacancies within the surface lattice is reported.
Abstract: Rationally generating oxygen vacancies in electrocatalysts is an important approach to modulate the electrochemical activity of a catalyst. Herein, we report a remarkable enhancement in oxygen reduction reaction (ORR) activity of NiCo2O4 supported on hollow carbon spheres (HCS) achieved through generating abundant oxygen vacancies within the surface lattice. This catalyst exhibits enhanced ORR activity (larger limiting current density of ∼−5.8 mA cm–2) and higher stability (∼90% retention after 40 000 s) compared with those of NiCo2O4/HCS and NiCo2O4. The results of X-ray photoelectron spectroscopy (XPS) characterizations suggest that the introduction of oxygen vacancies optimizes the valence state of active sites. Furthermore, we carried out density functional theory (DFT) calculations to further confirm the mechanism of oxygen vacancies, and results show that oxygen vacancies enhance the density of states (DOS) near the Fermi level, decrease work function, and lower the calculated overpotential of NiCo2O4.